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Böhme, Christoph. "Dynamics of spin-dependent charge carrier recombination." [S.l.] : [s.n.], 2003. http://archiv.ub.uni-marburg.de/diss/z2003/0183.
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Mickevičius, Jūras. "Carrier recombination in wide-band-gap nitride semiconductors." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20091121_102304-00016.
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The thesis is dedicated to carrier recombination investigations in wide-band-gap semiconductors and their structures. The complex experimental studies were performed by combining several different techniques. Carrier dynamics in GaN epilayers were investigated under extremely low and high excitation conditions. A new method for interpreting photoluminescence decay kinetics was suggested by interrelating luminescence and light-induced grating decay transients. The new approach for studies of yellow band in GaN was shown by linking the carrier lifetime with yellow band intensity. Two AlGaN epilayers grown by different novel growth techniques were compared and the factors limiting carrier lifetime were identified. Moreover, more evidence on alloy mixing and band potential fluctuations in AlGaN was provided by our study. Essential knowledge was attained about carrier dynamics in high-Al-content AlGaN/AlGaN multiple quantum well structures: the influence of built-in electric field and carrier localization on carrier dynamics. Most of the samples under study were grown by MEMOCVDTM growth technique, and our study confirmed the high potential of this innovative growth technique for improving material quality.Disertacija skirta krūvininkų rekombinacijos tyrimams plačiatarpiuose nitridiniuose puslaidininkiuose bei jų dariniuose. Kompleksiniai eksperimentiniai tyrimai buvo atlikti naudojant kelias skirtingas metodikas. Atlikti krūvininkų dinamikos GaN sluoksniuose tyrimai labai žemų ir aukštų sužadinimų sąlygomis. Pasiūlytas naujas liuminescencijos gesimo kinetikų interpretavimo metodas, siejant liuminescencijos ir šviesa indukuotų dinaminių gardelių kinetikas. Naujas požiūris į geltonosios liuminescencijos juostą GaN sluoksniuose leido susieti geltonosios liuminescencijos intensyvumą su krūvininkų gyvavimo trukme. Skirtingomis technologijomis augintų AlGaN sluoksnių palyginimas suteikė informacijos apie juostos potencialo fliuktuacijas bei krūvininkų gyvavimo trukmę ribojančius veiksnius AlGaN medžiagose. Atskleista naujų krūvininkų dinamikos daugialakštėse AlGaN/AlGaN kvantinėse duobėse ypatumų – vidinio elektrinio lauko bei kvantinės duobės pločio fliuktuacijų sąlygotos lokalizacijos įtaka krūvininkų dinamikai. Dauguma tirtų bandinių buvo auginti naudojant MEMOCVDTM technologiją ir tyrimai patvirtino šios technologijos potencialą siekiant pagerinti medžiagų kokybę.
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Reith, Charis. "Spin relaxation and carrier recombination in GaInNAs multiple quantum wells." Thesis, University of St Andrews, 2007. http://hdl.handle.net/10023/160.
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Electron spin relaxation and carrier recombination were investigated in gallium indium nitride arsenide (GaInNAs) multiple quantum wells, using picosecond optical pulses. Pump-probe experiments were carried out at room temperature, using pulses produced by a Ti:sapphire pumped optical parametric oscillator. The peak wavelengths of the excitonic resonances for the quantum well samples were identified using linear absorption measurements, and were found to be in the range 1.25µm-1.29µm. Carrier recombination times were measured for three samples of varying nitrogen content, and were observed to decrease from 548 to 180ps as nitrogen molar fractions were increased in the range 0.45-1.24%. Carrier recombination times were also measured for samples which had undergone a post-growth annealing process, and were found to be signicantly shorter compared to times measured for as-grown samples. Electron spin relaxation time was investigated for samples with quantum well widths in the range 5.8-8nm, and was found to increase with increasing well width, (i.e. decreasing quantum confinement energy), a trend predicted by both D'Yakonov-Kachorovskii and Elliott-Yafet models of spin relaxation in quantum wells. In a further study, longer spin relaxation times were exhibited by samples containing higher molar fractions of nitrogen, but having nominally constant quantum well width. Spin relaxation times increased from 47ps to 115ps for samples containing nitrogen concentrations in the range 0.45-1.24%. Decreases in spin relaxation time were observed in the case of those samples which had been annealed post-growth, compared to as-grown samples. Finally, all-optical polarisation switching based on spin relaxation of optically generated carriers in GaInNAs multiple quantum wells was demonstrated.
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Olszak, Peter D. "Nonlinear absorption and free carrier recombination in direct gap semiconductors." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4620.
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Nonlinear absorption of Indium Antimonide (InSb) has been studied for many years, yet due to the complexity of absorption mechanisms and experimental difficulties in the infrared, this is still a subject of research. Although measurements have been made in the past, a consistent model that worked for both picosecond and nanosecond pulse widths had not been demonstrated. In this project, temperature dependent two-photon (2PA) and free carrier absorption (FCA) spectra of InSb are measured using femtosecond, picosecond, and nanosecond IR sources. The 2PA spectrum is measured at room temperature with femtosecond pulses, and the temperature dependence of 2PA and FCA is measured at 10.6[micro]meters using a nanosecond CO[sub]2 laser giving results consistent with the temperature dependent measurements at several wavelengths made with a tunable picosecond system. Measurements over this substantial range of pulse widths give results for FCA and 2PA consistent with a recent theoretical model for FCA. While the FCA cross section has been generally accepted in the past to be a constant for the temperatures and wavelengths used in this study, this model predicts that it varies significantly with temperature as well as wavelength. Additionally, the results for 2PA are consistent with the band gap scaling (Eg[super]-3) predicted by a simple two parabolic band model. Using nanosecond pulses from a CO?éé laser enables the recombination rates to be determined through nonlinear transmittance measurements. Three-photon absorption is also observed in InSb for photon energies below the 2PA band edge. Prior to this work, data on three-photon absorption (3PA) in semiconductors was scarce and most experiments were performed over narrow spectral ranges, making comparison to the available theoretical models difficult. There was also disagreement between the theoretical results generated by different models, primarily in the spectral behavior.; Therefore, we studied the band gap scaling and spectra of 3PA in several semiconductors by the Z-scan technique. The 3PA coefficient is found to vary as (Eg[super]-7), as predicted by the scaling rules of simple two parabolic band models. The spectral behavior, which is considerably more complex than for 2PA, is found to agree well with a recently published theory based on a four-band model.ID: 029050684; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references.
Ph.D.
Doctorate
Optics and Photonics
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McConville, Daniel. "Carrier recombination in dilute nitride based near infrared semiconductor lasers." Thesis, University of Surrey, 2007. http://epubs.surrey.ac.uk/844606/.
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This thesis describes and quantifies the roles of the different carrier recombination processes within near infrared GaInNAs single quantum well laser devices. An initial review of the published literature relating to GaInNAs highlighted a number of areas where investigation of the material system would be interesting, including changing the nitrogen concentration, the barrier material, the incorporated strain and the growth technique. We find that at 1.3mum, at room temperature, the threshold current of MBE grown devices is composed of 70% Auger recombination, 25% monomolecular recombination and 5% radiative recombination, and at 1.5mum, 61% Auger recombination, 31% monomolecular recombination and 8% radiative recombination. In absolute terms Auger is the most significant current path over the entire wavelength range. This dominance of Auger recombination was also found to be responsible for the poor temperature stability of these devices, with the Auger recombination component typically having a T0 ~50K. Calculations of the threshold carrier density along with a break-down of the threshold current were used to evaluate the recombination coefficients; these were found to be A = 4x108 (s-1), B - 3x10-11 (cm3s-1) and C = 6x10-29 (cm6s-1) at 1.3mum, and A = 8x108 (s-1), B = 6x10 -11 (cm3s-1) and C = 1.2x10-28 (cm6s-1) at 1.5mum. These values are comparable to those of InGaAsP and AlGaInAs. Furthermore, these investigations suggest that carrier leakage is negligible in these devices. Hydrostatic pressure techniques were used to study the effect of changing the band gap on the recombination processes occurring within the devices; this highlighted the importance of the band anti crossing interaction between the conduction band edge and the nitrogen level in GaInNAs devices where it was seen that a longer wavelengths this interaction appears to be weaker. Replacing GaAs barriers with GaNAs barriers leads to a ~ 15% reduction in the magnitude of the monomolecular current present, indicating that this should be a useful method of optimising the growth of GaInNAs. An investigation into the effect of strain incorporated within the quantum well of the ~1.5mum devices highlighted the possibility of its use to reduce the threshold carrier density and thus the Auger current within these devices. Since this work was based on single quantum well devices it shows that the GaInNAs material system is a very promising alternative to conventional InGaAsP and AlGaInAs devices which rely upon multiple quantum wells.
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Thota, Venkata Ramana Kumar. "Tunable Optical Phenomena and Carrier Recombination Dynamics in III-V Semiconductor Nanostructures." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1451807323.
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Naidu, Deepal. "Characterisation of lateral carrier out-diffusion and surface recombination in ridge waveguide devices." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/54892/.
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As laser devices are scaled down in size and involve the use of photonic structures etched through the active layer - a trend driven by the desire to improve device performance and functionality for future applications in optoelectronic integrated circuits - performance limiting mechanisms such as an increasing internal optical loss, deteriorating gain-mode overlap, lateral carrier out-diffusion and surface recombination can inflict restrictions on the further miniaturisation and overall performance. In this project I have separately evaluated the relative impact of these mechanisms using ridge waveguide devices, with particular focus on the behaviour of the lateral out-diffusion and the surface-recombination mechanism in quantum-dot and quantum-well active regions. The approach of separately evaluating the relative impact of each mechanism is made possible by using the multisection characterisation technique. By this means the investigation in this study circumvents the problems associated with previous studies on lateral out-diffusion and surface recombination. Moreover, it furthers the overall analysis by measuring the effects as a function of injection-level and quantifying the change in non-radiative current density and overall internal quantum efficiency. In quantum-dot shallow etched ridge waveguide devices (S-RWG) it is found that the mechanism of an increasing internal optical mode loss and increasing lateral out-diffusion current are the principal causes for the apparent increase in threshold current density with reducing ridge width from 10 to 4 um. The internal optical loss was found to increase by a factor of 2.3 over this range and the non-radiative current density due to lateral out diffusion increased by a factor of 1.14 at an injection-level of 121 meV. The mechanism of a deteriorating gain-mode overlap was negligible in this range. Measurements of the lateral ambipolar diffusion length found that in self-assembled quantum-dot/wetting-layer systems the lateral ambipolar diffusion process can be inhibited in one of two ways: one good and one bad. This original result showed that the good way, in terms of benefiting the overall device performance, involves the inhibition due to three-dimensional carrier confinement in the quantum-dots. The other involves populating the wetting-layer to a point where a higher order non-radiative recombination process reduces the average carrier lifetime and hence ambipolar diffusion length. Both regimes can reduce the loss of carriers to lateral carrier out-diffusion and surface recombination however the latter is at the expense of increasing other non-radiative recombination processes. The ambipolar diffusion length was also found to be temperature dependent with a smaller diffusion length at lower temperatures. At 350 K the lateral ambipolar diffusion length varied from 0.75 um to a maximum value of 1.5 um over the injection-level range 65 meV to 84 meV. At 300 K the ambipolar diffusion length was smaller than 0.75 um for injection-levels below 121 meV. In quantum-well deep etched ridge waveguide devices (D-RWG) it was found that the D-RWG structure allowed much smaller ridge width (<2.8 (am) devices than S-RWG structures before as significant an increase in internal optical loss occurred. However, once a significant interaction of the wave amplitude and rough sidewalls does occur, the scattering loss in D-RWG structures was much more strongly affected. The D-RWG structure also provided no deterioration in the gain-mode overlap in the range 29 to 1.9 um. A power law analysis of the measured non-radiative current density revealed that the principal threshold increasing mechanism in D-RWG devices was surface recombination. The fractional increase in threshold non-radiative current density for 1.5 mm lasers was significant. From a width of 29.1 to 9.6 um the non-radiative current density increased by factor of 2 to a value of 462 A/cm2, and from 29.1 to 2.8 um by a factor of 11 to 2612 A/cm2. The overall internal quantum efficiency at threshold in the 1.5 mm lasers was measured to significantly decrease as the ridge width was reduced. This is a direct consequence of an increasing fraction of applied current recombining via surface recombination. The measured decrease from a ridge width of 29.1 um to 2.8 um was 16.6 % to 1.8 %. By characterizing the performance differences in the two RWG structures and the threshold increasing mechanisms of lateral out-diffusion and surface recombination in quantum-dot and quantum-well active regions respectively, knowledge of the criteria required for designing better devices for further miniaturisation and improved threshold performance was gained.
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Ivanov, Ruslan. "Impact of carrier localization on recombination in InGaN quantum wells with nonbasal crystallographic orientations." Doctoral thesis, KTH, Optik och Fotonik, OFO, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-214599.
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The modern InGaN technology demonstrates high efficiencies only in the blue spectral region and low current operation modes. The growth of InGaN quantum wells (QWs) on nonbasal crystallographic planes (NBP) has potential to deliver high-power blue and green light emitting diodes and lasers. The emission properties of these QWs are largely determined by the localization of carriers in the minima of spatially inhomogeneous band potential, which affects the recombination dynamics, spectral characteristics of the emission, its optical polarization and carrier transport. Understanding it is crucial for increasing the efficiency of NBP structures to their theoretical limit. In this thesis, the influence of carrier localization on the critical aspects of light emission has been investigated in semipolar and nonpolar InGaN QWs. For this purpose, novel multimode scanning near-field optical microscopy configurations have been developed, allowing mapping of the spectrally-, time-, and polarization-resolved emission. In the nonpolar QW structures the sub-micrometer band gap fluctuations could be assigned to the selective incorporation of indium on different slopes of the undulations, while in the smoother semipolar QWs – to the nonuniformity of QW growth. The nanoscale band potential fluctuations and the carrier localization were found to increase with increasing indium percentage in the InGaN alloy. In spite to the large depth of the potential minima, the localized valence band states were found to retain properties of the corresponding bands. The reduced carrier transfer between localization sites has been suggested as a reason for the long recombination times in the green-emitting semipolar QWs. Sharp increase of the radiative lifetimes has been assigned to the effect of nanoscale electric fields resulting from nonplanar QW interfaces. Lastly, the ambipolar carrier diffusion has been measured, revealing ~100 nm diffusion length and high anisotropy.QC 20170919
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Sieland, Fabian [Verfasser], and Detlef W. [Akademischer Betreuer] Bahnemann. "Fractal charge carrier recombination kinetics in photocatalytic systems / Fabian Sieland ; Betreuer: Detlef W. Bahnemann." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2018. http://d-nb.info/1172414157/34.
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Sieland, Fabian Verfasser], and Detlef [Akademischer Betreuer] [Bahnemann. "Fractal charge carrier recombination kinetics in photocatalytic systems / Fabian Sieland ; Betreuer: Detlef W. Bahnemann." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2018. http://nbn-resolving.de/urn:nbn:de:101:1-2018112901094242866616.
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Pattanapanishsawat, Piyapong. "Study of Surface Modification and Effect of Temperature on Charge Carrier Generation and Recombination." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1281364113.
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Amaku, Afi. "A study of the electrical properties of point and extended defects in silicon." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339355.
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Brandt, Matthias. "Influence of the electric polarization on carrier transport and recombination dynamics in ZnO-based heterostructures." Doctoral thesis, Universitätsbibliothek Leipzig, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-61074.
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Die vorliegende Arbeit befasst sich mit dem Einfluss der elektrischen Polarisation auf Eigenschaften freier Träger in ZnO basierten Halbleiterheterostrukturen. Dabei werden insbesondere Transporteigenschaften freier Träger sowie deren Rekombinationsdynamik untersucht. Die Arbeit behandelt vier inhaltliche Schwerpunkte. Der erste Schwerpunkt liegt auf den physikalischen Eigenschaften der verwendeten Materialen, hier wird der Zusammenhang der Bandlücke und der Gitterkonstanten von MgZnO Dünnfilmen und deren Magnesiumgehalt beschrieben. Weiterhin wird die Morphologie solcher Filme diskutiert. Auf unterschiedliche Substrate und Abscheidebedingungen wird dabei detailliert eingegangen. Der zweite Schwerpunkt behandelt die Eigenschaften undotierter und phosphordotierter ZnO und MgZnO Dünnfilme. Die strukturellen, Transport- und Lumineszenzeigenschaften werden hier verglichen und Rückschlüsse auf die Züchtungsbedingungen gezogen. Im dritten Schwerpunkt werden Quanteneffekte an ZnO/MgZnO Grenzflaechen behandelt. Hierbei wird insbesondere auf den Einfluss der elektrischen Polarisation eingegangen. Die Präsenz eines zweidimensionalen Elektronengases wird nachgewiesen, und die notwendigen Bedingungen zur Entstehung des sogenannten qunatum confined Stark-effects werden dargelegt. Insbesondere wird hier auf züchtungsrelevante Parameter eingegangen. Den vierten Schwerpunkt stellen Kopplungsphänomene in ZnO/BaTiO3 Heterostrukturen dar. Dabei werden zuerst die experimentell beobachten Eigenschaften verschiedener Heterostrukturen die auf unterschiedlichen Substraten gezüchtet wurden aufgezeigt. Hier stehen strukturelle und Transporteigenschaften im Vordergrund. Ein Modell zur Beschreibung der Ausbildung von Raumladungszonen in derartigen Heterostrukturen wird eingeführt und zur Beschreibung der experimentellen Ergebnisse angewandt. Die Nutzbarkeit der ferroelektrischen Eigenschaften des Materials BaTiO3 in Kombination mit halbleitendem ZnO wurden untersucht. Hierzu wurden ferroelektrische Feldeffekttransistoren unter Verwendung beider Materialien hergestellt. Die prinzipielle Eignung der Bauelemente als nichtflüchtige Speicherelemente wurde nachgewiesen.
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Gasparini, Nicola [Verfasser], and Christoph J. [Gutachter] Brabec. "Controlling charge carrier recombination in ternary organic solar cells / Nicola Gasparini ; Gutachter: Christoph J. Brabec." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2017. http://d-nb.info/1136473254/34.
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Moen, Kurt Andrew. "Modeling of minority carrier recombination and resistivity in sige bicmos technology for extreme environment applications." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26642.
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Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.Committee Chair: Cressler, John; Committee Member: Citrin, David; Committee Member: Shen, Shyh-Chiang. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Michel, Christoph. "Theoretical studies of spin dependent transport phenomena [transport in magnetic semiconductors ; spin dependent charge carrier recombination]." Göttingen Cuvillier, 2007.
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Aytac, Yigit. "Time-resolved measurements of charge carrier dynamics in Mwir to Lwir InAs/InAsSb superlattices." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2039.
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All-optical time-resolved measurement techniques provide a powerful tool for investigating critical parameters that determine the performance of infrared photodetector and emitter semiconductor materials. Narrow-bandgap InAs/GaSb type-II superlattices (T2SLs) have shown great promise as next generation materials, due to superior intrinsic properties and versatility. Unfortunately, InAs/GaSb T2SLs are plagued by parasitic Shockley-Read-Hall recombination centers that shorten the carrier lifetime and limit device performance. Ultrafast pump-probe techniques and time-resolved differential-transmission measurements are used here to demonstrate that "Ga-free" InAs/InAs₁₋xSbx T2SLs and InAsSb alloys do not have this same limitation and thus have significantly longer carrier lifetimes. Measurements of unintentionally doped MWIR and LWIR InAs/InAs₁₋xSbx T2SLs demonstrate minority carrier (MC) lifetimes of 18.4 µs and 4.5 µs at 77 K, respectively. This represents a more than two order of magnitude increase compared to the 90 ns MC lifetime measured in a comparable MWIR and LWIR InAs/GaSb T2SL. Through temperature-dependent differential-transmission measurements, the various carrier recombination processes are differentiated and the dominant recombination mechanisms identified for InAs/InAs₁₋xSbx T2SLs. These results demonstrate that these Ga-free materials are viable options over InAs/GaSb T2SLs and potentially bulk Hg₁₋xCdxTe photodetectors.
In addition to carrier lifetimes, the drift and diusion of excited charge carriers through the superlattice layers (i.e. in-plane transport) directly aects the performance of photo-detectors and emitters. All-optical ultrafast techniques were successfully used for a direct measure of in-plane diffusion coeffcients in MWIR InAs/InAsSb T2SLs using a photo-generated transient grating technique at various temperatures. Ambipolar diffusion coefficients of approximately 60 cm²/s were reported for MWIR InAs/InAs₁₋xSbxT2SLs at 293 K.
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Turcu, Mircea Cassian. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1086247686828-95497.
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This work investigates the defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In1-xGax)(Se1-ySy)2 chalcopyrite thin films and the interrelationship with the alloy composition. Photoluminescence spectroscopy of investigated Cu-poor Cu(In,Ga)(Se,S)2 layers generally shows broad emission lines with the corresponding maxima shifting towards higher energies under decreasing temperature or under increasing excitation power. Admittance spectroscopy of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 chalcopyrite devices shows that the activation energies of the dominant defect distributions involving donors at the CdS/absorber interface and deep acceptors in the chalcopyrite bulk, increase upon alloying CuInSe2 with S. The band alignments within the Cu(In1-xGax)(Se1-ySy)2 system are determined using the energy position of the bulk acceptor state as a reference. The band gap enlargement under Ga alloying is accommodated almost exclusively in the rise of the conduction band edge, whereas the increase of band gap upon alloying with S is shared between comparable valence and conduction band offsets. The extrapolated band discontinuities [delta]EV(CuInSe2/CuInS2) = -0.23 eV, [delta]EC(CuInSe2/CuInS2) = 0.21 eV, [delta]EV(CuInSe2/CuGaSe2) = 0.036 eV, and [delta]EC(CuInSe2/CuGaSe2) = 0.7 eV are in good agreement with theoretical predictions. Current-voltage analysis of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 devices reveals recombination barriers which follow the band gap energy of the absorber irrespective of alloy composition, as expected for dominant recombination in the chalcopyrite bulk. In turn, the recombination at the active junction interface prevails in Cu-rich devices which display substantially smaller barriers when compared to the band gap energy of the absorber. The result indicates that the Cu-stoichiometry is the driving compositional parameter for the charge carrier recombination in the chalcopyrite heterojunctions under investigations.
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Danhof, Julia [Verfasser], and Ulrich T. [Akademischer Betreuer] Schwarz. "Local charge carrier diffusion and recombination in InGaN quantum wells = Lokale Ladungsträgerdiffusion und -rekombination in InGaN Quantentrögen." Freiburg : Universität, 2013. http://d-nb.info/1123477663/34.
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Turcu, Mircea Cassian. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys." Doctoral thesis, Technische Universität Dresden, 2003. https://tud.qucosa.de/id/qucosa%3A24342.
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This work investigates the defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In1-xGax)(Se1-ySy)2 chalcopyrite thin films and the interrelationship with the alloy composition. Photoluminescence spectroscopy of investigated Cu-poor Cu(In,Ga)(Se,S)2 layers generally shows broad emission lines with the corresponding maxima shifting towards higher energies under decreasing temperature or under increasing excitation power. Admittance spectroscopy of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 chalcopyrite devices shows that the activation energies of the dominant defect distributions involving donors at the CdS/absorber interface and deep acceptors in the chalcopyrite bulk, increase upon alloying CuInSe2 with S. The band alignments within the Cu(In1-xGax)(Se1-ySy)2 system are determined using the energy position of the bulk acceptor state as a reference. The band gap enlargement under Ga alloying is accommodated almost exclusively in the rise of the conduction band edge, whereas the increase of band gap upon alloying with S is shared between comparable valence and conduction band offsets. The extrapolated band discontinuities [delta]EV(CuInSe2/CuInS2) = -0.23 eV, [delta]EC(CuInSe2/CuInS2) = 0.21 eV, [delta]EV(CuInSe2/CuGaSe2) = 0.036 eV, and [delta]EC(CuInSe2/CuGaSe2) = 0.7 eV are in good agreement with theoretical predictions. Current-voltage analysis of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 devices reveals recombination barriers which follow the band gap energy of the absorber irrespective of alloy composition, as expected for dominant recombination in the chalcopyrite bulk. In turn, the recombination at the active junction interface prevails in Cu-rich devices which display substantially smaller barriers when compared to the band gap energy of the absorber. The result indicates that the Cu-stoichiometry is the driving compositional parameter for the charge carrier recombination in the chalcopyrite heterojunctions under investigations.
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Kiermasch, David [Verfasser], Vladimir [Gutachter] Dyakonov, and Christian [Gutachter] Schneider. "Charge Carrier Recombination Dynamics in Hybrid Metal Halide Perovskite Solar Cells / David Kiermasch ; Gutachter: Vladimir Dyakonov, Christian Schneider." Würzburg : Universität Würzburg, 2020. http://d-nb.info/1214594123/34.
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Kudriashova, Liudmila [Verfasser], Vladimir [Gutachter] Dyakonov, Sven [Gutachter] Höfling, and Bernd [Gutachter] Engels. "Photoluminescence Reveals Charge Carrier Recombination in Organic and Hybrid Semiconductors / Liudmila Kudriashova ; Gutachter: Vladimir Dyakonov, Sven Höfling, Bernd Engels." Würzburg : Universität Würzburg, 2019. http://d-nb.info/1202013635/34.
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Richter, Johannes Martin. "Charge carrier relaxation in halide perovskite semiconductors for optoelectronic applications." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275568.
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Lead halide perovskites have shown remarkable device performance in both solar cells and LEDs. Whilst the research efforts so far have been mainly focussed on device optimisation, little is known about the photophysical properties. For example, the nature of the bandgap is still debated and an indirect bandgap due to a Rashba splitting has been suggested. In this thesis, we study the early-time carrier relaxation and its impact on photoluminescence emission. We first study ultrafast carrier thermalization processes using 2D electronic spectroscopy and extract characteristic carrier thermalization times from below 10 fs to 85 fs. We then investigate the early-time photoluminescence emission during carrier cooling. We observe that the luminescence signal shows a rise over 2 picoseconds in CH3NH3PbI3 while carriers cool to the band edge. This shows that luminescence of hot carriers is slower than that of cold carriers, as is found in direct gap semiconductors. We conclude that electrons and holes show strong overlap in momentum space, despite the potential presence of a small band offset arising from a Rashba effect. Recombination and device performance of perovskites are thus better described within a direct bandgap model. We finally study carrier recombination in perovskites and the impact of photon recycling. We show that, for an internal photoluminescence quantum yield of 70%, we measure external yields as low as 15% in planar films, where light out-coupling is inefficient, but observe values as high as 57% in films on textured substrates that enhance out-coupling. We study the photo-excited carrier dynamics and use a rate equation to relate radiative and non-radiative recombination events to measured photoluminescence efficiencies. We conclude that the use of textured active layers has the ability to improve power conversion efficiencies for both LEDs and solar cells.
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Ichikawa, Shuhei. "Fundamental Study on Carrier Recombination Processes in AlGaN-related Materials and their Structural Designs toward Highly Efficient Deep-UV Emitters." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225608.
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Turcu, Mircea C. [Verfasser]. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys / Mircea C Turcu." Aachen : Shaker, 2004. http://d-nb.info/1170529550/34.
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Asada, Satoshi. "Improvement of ON-Characteristics in SiC Bipolar Junction Transistors by Structure Designing Based on Analyses of Material Properties and Carrier Recombination." Kyoto University, 2019. http://hdl.handle.net/2433/242510.
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Ringel, Brett Logan. "Investigation of Mesa Etched Antimonide Detectors Using Time Resolved Microwave Reflectance." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1589153635130203.
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Wehrenfennig, Christian. "Ultrafast spectroscopy of charge separation, transport and recombination processes in functional materials for thin-film photovoltaics." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:1f812413-4a2f-418f-a7fd-d749e88cc2e1.
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Dye-sensitized solar cells (DSSCs) and perovskite solar cells are emerging as promising potential low-cost alternatives to established crystalline silicon photovoltaics. Of the employed functional materials, however, many fundamental optoelectronic properties governing photovoltaic device operation are not sufficiently well understood. This thesis reports on a series of studies using ultrafast THz and photoluminescence spectroscopy on two classes of such materials, providing insight into the dynamics of charge-transport and recombination processes following photoexcitation. For TiO2-nanotubes, which have been proposed as easy-to-fabricate electron transporters for DSSCs, fast, shallow electron trapping is identified as a limiting factor for efficient charge collection. Trapping lifetimes are found to be about an order of magnitude shorter than in the prevalently employed sintered nanoparticles under similar excitation conditions and trap saturation effects are not observed, even at very high excitation densities. In organo-lead halide perovskites - specifically CH3NH3PbI3 and CH3NH3PbI3-xClx, which have only recently emerged as highly efficient absorbers and charge transporters for thin-film solar cells, carrier mobilities and fundamental recombination dynamics are revealed. Extremely low bi-molecular recombination rates at least four orders of magnitude below the prediction of Langevin's model are found as well as relatively high charge-carrier mobilities in comparison to other solution-processable materials. Furthermore a very low influence of trap-mediated recombination channels was observed. Due to a combination of these factors, diffusion lengths reach hundreds of nanometres for CH3NH3PbI3 and several microns for CH3NH3PbI3-xClx. These results are shown to hold for both, solution processed and vapour-deposited CH3NH3PbI3-xClx and underline the superb suitability of the materials as absorbers in solar cells, even in planar heterojunction architectures. The THz-frequency spectrum of the conductivity of the investigated perovskites is consistent with Drude-like charge transport additionally exhibiting weak signatures of phonon coupling. These coupling effects are also reflected in the luminescence of CH3NH3PbI3-xClx, where they are believed to be the cause of the observed homogeneous spectral broadening. Further photoluminescence measurements were performed at temperatures between 4 K and room temperature to study the nature of recombination pathways in the material.
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Roland, Steffen [Verfasser], and Dieter [Akademischer Betreuer] Neher. "Charge carrier recombination and open circuit voltage in organic solar cells : from bilayer-model systems to hybrid multi-junctions / Steffen Roland ; Betreuer: Dieter Neher." Potsdam : Universität Potsdam, 2017. http://d-nb.info/1218402458/34.
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McGarry, Stephen. "Irradiated silicon particle detectors." Thesis, Lancaster University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369468.
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Rauh, Daniel [Verfasser], and Vladimir [Gutachter] Dyakonov. "Impact of Charge Carrier Density and Trap States on the Open Circuit Voltage and the Polaron Recombination in Organic Solar Cells / Daniel Rauh. Gutachter: Vladimir Dyakonov." Würzburg : Universität Würzburg, 2013. http://d-nb.info/1112040021/34.
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López, Salas José Fabio [Verfasser], Stephan J. [Akademischer Betreuer] Heise, Jürgen [Akademischer Betreuer] Parisi, and Petra [Akademischer Betreuer] Groß. "Modeling and simulation of charge carrier recombination dynamics in Cu(In,Ga)Se2 thin-film solar cells / José Fabio López Salas ; Stephan J. Heise, Jürgen Parisi, Petra Groß." Oldenburg : BIS der Universität Oldenburg, 2018. http://d-nb.info/1161096841/34.
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López, Salas José Fabio Verfasser], Stephan J. [Akademischer Betreuer] Heise, Jürgen [Akademischer Betreuer] [Parisi, and Petra [Akademischer Betreuer] Groß. "Modeling and simulation of charge carrier recombination dynamics in Cu(In,Ga)Se2 thin-film solar cells / José Fabio López Salas ; Stephan J. Heise, Jürgen Parisi, Petra Groß." Oldenburg : BIS der Universität Oldenburg, 2018. http://d-nb.info/1161096841/34.
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Kulikovsky, Lazar. "Experimentelle Untersuchung der Ladungsträgerdynamik in photorefraktiven Polymeren." Phd thesis, Universität Potsdam, 2003. http://opus.kobv.de/ubp/volltexte/2005/130/.
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Die heutige optische Informationsverarbeitung erfordert neue Materialien, die Licht effektiv verarbeiten, steuern und speichern können. Photorefraktive (PR) Materialien sind dafür sehr interessant. In diesen Materialien entsteht bei inhomogener Beleuchtung (z.B. mit einem Intererenzmuster) über Ladungsträgergenerierung und Einfang der Ladungsträger in Fallen ein Raumladungsfeld. Dieses wird über den elektrooptischen Effekt in eine räumliche Modulation des Brechungsindex umgesetzt. Letztendlich führt somit die inhomogene Beleuchtung eines PR-Materials zu einer räumlich variierenden Änderung des Brechungsindex. Vor ca. 10 Jahren wurde entdeckt, dass auch Polymere einen PR-Effekt aufweisen können. Die Ansprechzeit dieser Materialien wird dabei wesentlich durch die Dynamik der Ladungsträger (bestimmt durch Erzeugung, Transport, Einfang in Fallen etc.) begrenzt. Bis zu Beginn dieser Arbeit war es noch nicht gelungen, einen quantitativen Zusammenhang zwischen der Ladungsträgerdynamik und der Ansprechzeit des PR-Effekts experimentell nachzuweisen. In dieser Arbeit wird ein Weg aufgezeigt, durch photophysikalische Experimente unter verschiedenen Beleuchtungsbedingungen alle photophysikalischen Größen experimentell zu bestimmen, die den Aufbau des Raumladungsfelds in organischen photorefraktiven Materialien bestimmen. So konnte durch Experimente unter Beleuchtung mit kurzen Einzelpulsen sowohl die Beweglichkeit der freien Ladungsträger als auch die charakteristischen Parameter flacher Fallen ermittelt werden. Zur Bestimmung der Dichte tiefer Fallen wurde die Intensitätsabhängigkeit des stationären Photostroms untersucht. Durch die analytische Lösung des bestimmenden Gleichungssystems konnte gezeigt werden, dass die Sublinearität der Intensitätsabhängigkeit des Photostroms primär mit dem Verhältnis zwischen Entleerungs- und Einfangkoeffizienten tiefer Fallen korreliert. Zur unabhängigen Bestimmung des Entleerungskoeffizienten der tiefen Fallen wurden Doppelpulsexperimente mit variabler Verzögerungszeit zwischen den Pulsen verwendet. Mit den erhaltenen Parametern konnte dann das untere Limit der zum Aufbau des Raumladungsfelds notwendigen Zeit abgeschätzt werden. Diese Werte wurden mit den gemessenen photorefraktiven Ansprechzeiten verglichen. Es zeigt sich, dass weder die Photogeneration noch der Transport der Ladungsträger die Geschwindigkeit des Aufbaus des Raumladungsfeldes limitiert. Stattdessen konnte erstmals quantitativ nachgewiesen werden, dass die Dynamik des Raumladungsfelds in den hier untersuchten PR-Materialien durch das Füllen tiefer Fallen mit photogenerierten Ladungsträgern bestimmt wird. Dabei spielt das Verhältnis zwischen dem Einfang- und dem Rekombinationskoeffizienten eine wesentliche Rolle. Weiterhin wurde die Dynamik des Aufbaus des Raumladungsfelds bei unterschiedlichen Vorbeleuchtungsbedingungen quantitativ simuliert und mit den experimentellen PR-Transienten verglichen. Die gute Übereinstimmung zwischen den simulierten und gemessenen Transienten erlaubte es abschließend, die kritischen Parameter, die die Dynamik des PR-Effekts in den untersuchten Polymeren begrenzen, zu identifizieren.The ongoing development of information processing requires new materials that are capable of effective light modulation, processing or storage. Photorefractive (PR) materials characterized by a reversible light-induced change of the refractive index have been effectively used for different optical applications. When a photorefractive medium is inhomogeneously irradiated, using for example an interference pattern, the generation, transport and trapping of the charge carriers results in the formation of a space charge field. The spatial modulation of the space charge field is transformed through the electro-optical effect into a modulation of the refractive index.
While photorefractive crystals are well known since the discovery of the PR effect in 1966, the photorefractive effect in polymers has only recently been demonstrated. The flexibility of material composition and thus its parameters along with easy processability of polymer materials essentially extends the range of possible applications of photorefractive materials. The response time of PR polymers is defined by the charge carrier dynamics including generation, transport, trapping etc. But a relation between the charge carriers dynamics and the response time of PR effect has not yet been proven experimentally. In this work a method for the experimental determination of all photo-physical parameters defining the formation of the space charge field in organic photorefractive materials has been proposed for the first time. It is based on the analysis of the photocurrent measured under different irradiation conditions such as continuous and pulse irradiation with different intensities, the variation of the pulse length, the number of pulses or the delay between pulses. Thus, the irradiation with single short pulses allowed to determine the mobility of free charge carriers as well as the characteristic parameters of shallow traps. In order to determine the density of deep traps, the intensity dependence of the steady-state photocurrent was investigated. The determining system of equations was analytically solved and it has been shown that the sublinear dependence of the photocurrent on intensity is primary correlated with the ratio of detrapping and trapping coefficients for deep traps. The detrapping coefficient of deep traps was independently determined from double-pulse experiments in which the delay between two pulses was varied. The dynamics of the space charge field formation has been numerically simulated, using the obtained photophysical parameters, and proven to coincide well with the experimentally determined dynamics of the PR effect. This allowed to relate the parameters of the individual processes participating in the formation of the space charge field to the dynamics of the PR effect in the investigated polymers. These results show that neither photogeneration nor transport of the charge carriers do limit the formation of the space charge field. It is demonstrated that in the investigated PR materials the dynamics of the space charge field is limited by the filling of deep traps with the photogenerated charge carriers.
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Ihlal, Ahmed. "Analyses quantitatives par sem/ebic des defauts recombinants dans les semiconducteurs polycristallins : influence des traitements thermiques sur l'activite electrique des bicristaux de silicium." Caen, 1988. http://www.theses.fr/1988CAEN2007.
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Etude quantitative , par la methode ebic, de la recombinaison des porteurs minoritaires dans des bicristaux de silicium en fonction des traitements thermiques, entre 450 et 950**(o)c. Un developpement des phenomenes physiques regissant la creation de differentes theories conduisant au traitement quantitatif du signal ebic est presente. Selon le traitement thermique, le contraste des deux types de joints de grains evolue avec la temperature: vitese de recombinaison et longueur de diffusion varient avec la temperature de recuit
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Chaggar, Amrik Richard. "Tunneling injection and recombination of carriers in self-assembled quantum dots." Thesis, University of Nottingham, 2009. http://eprints.nottingham.ac.uk/10757/.
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This thesis describes an experimental investigation of the resonant injection of carriers into self-assembled indium arsenide (InAs) quantum dots incorporated in the intrinsic region of gallium arsenide (GaAs) p-i-n resonant tunneling diodes, and of the resulting electroluminescence spectrum associated with carrier recombination in the quantum dots, wetting layer and GaAs matrix. A series of devices of different designs have been measured and it is shown that bipolar resonant injection, i.e. resonant injection of both electrons andholes, into the zero-dimensional states provided by the InAs quantum dots is possible. It is shown that bias-tunable tunneling of carriers into the dots provides a means of controlling injection and light emission from a small number of individual dots within a large ensemble. Magnetotunneling spectroscopy is used to investigate the possibility that fluctuations in the potential profile of the GaAs emitter layer play a significant role in the carrier dynamics of such devices. We also show that the extent of carrier energy relaxation prior to recombination can be controlled by tailoring the morphology of the quantum dot layer. Additionally, a study into the phenomenon of low-temperature up-conversion electroluminescence (UCEL) is presented. Injection of carriers into the quantum dot states at an applied bias well below the GaAs flat-band condition results in near-band-edge GaAs electroluminescence, i.e., emission of photons with energies much larger than that supplied by the applied bias and the thermal energy. The origin of this UCEL is discussed and is attributed to carrier excitation resulting from (non-radiative) Auger recombination of electron-hole pairs in the quantum dot ground states.
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Sangal, Vartul. "Multilocus sequence typing analyses of Salmonella enterica subspecies enterica." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2009. http://dx.doi.org/10.18452/15883.
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Serovare von Salmonella enterica subspecies enterica sind im allgemeinen pathogen für Mensch und andere Säugetiere. In dieser Arbeit habe ich anhand eines “Multilocus Sequences Typing” Typisierungsschemas die Populationsstruktur einer der am häufigsten auftretenden Serovaren dieser Subspecies, das aus Menschen und Schlachttieren isolierte Serovar Newport charakterisiert. Dieses Schema wurde auch für die Charakterisierung von Isolaten derselben Subspecies aus humanen Dauerträgern und Reptilien verwandt, um zu bestimmen, ob Isolate aus diesen Quellen sich in ihrer Populationstruktur von denjenigen unterscheiden, die aus anderen Quellen isoliert wurden. Multilocus Sequences Typing ist eine weitgehend für die Untersuchung der Evolution und Populationsstruktur von einen breiten Spektrum von Organismen verwendete Technik. 400 - 600 bp lange Fragmente von 7 Haushaltsgenen wurden sequenziert, und jede einzelne Sequenz jedes einzelnen Gens wurde eine Allelnummer zugeordnet. Jede einzelne Allelkombination wurde einem Sequenztyp zugeordnet. Die so gewonnenen Daten wurden weiter analysiert. Drei “Lineages”, Newport-I, Newport-II und Newport-III, wurden innerhalb dieses Serovars identifiziert, die jeweils aus Menschen in Europa, Tieren und Menschen in Nordamerika isoliert wurden. Der Multiresistenz-Phänotyp wurde häufiger in Newport II gefunden, während die meisten Newport III Isolate pan-sensitiv waren. Verglichen mit anderen Serovaren war die Anzahl von “Lineages” innerhalb Newport höher als bei Enteritidis, Kentucky und Typhimurium, aber niedriger als bei Paratyphi B. Das heisst, die Serovare von S. enterica subspecies enterica variieren stark in ihrer Populationsstruktur. Die Sequenztypen in Isolaten aus humanen Dauerträgern waren im allgemeinen am häufigsten in Isolaten von klinischen Patienten und Tieren vorhanden. In der Mehrheit der Serovaren waren die meisten Isolate aus Patienten und Tieren genetisch identisch mit solchen, die aus gesunden Trägern isoliert wurden. Die genetische Variabilität war zwischen Isolaten aus diesen Quellen vergleichbar. Diese Ergebnissen deuten daraufhin, dass Salmonellen aus Dauerträgern sowie Isolate aus Patienten und Tieren derselben Population angehören. Die meisten Serovare aus Reptilienisolaten waren genetisch identisch mit denen von Menschen und warmblütigen Tieren. In den Serovaren Bovismorbificans, Decatur, Miami und Oranienburg hingegen waren die meisten Isolate aus Reptilien genetisch anders als Isolate aus anderen Wirten. Allerdings wurden nur wenige Isolate der Serovaren Bovismorbificans, Decatur und Miami aus Reptilien und nur wenige Isolate der Serovaren Oranienburg aus anderen Quellen getestet; eine grössere Anzahl von Isolaten müsste daher untersucht werden, um festzustellen ob diese genetischen Unterschiede statistich signifikant sind oder nicht.Serovars of Salmonella enterica subspecies enterica are generally pathogenic to humans and other mammals. In this study, I examined the population structure of one of the most common serovars of this subspecies isolated from humans and food animals, serovar Newport, using a multilocus sequence typing scheme. This scheme was also used to analyze isolates of this subspecies from chronic human carriers and reptiles to determine whether isolates from these sources represent distinct populations than those from other hosts. Multilocus sequence typing has extensively been used to study evolution and population structure of a wide range of organisms. 400-600 bp fragments of 7 housekeeping genes were sequenced and every unique sequence of each gene fragment was given a distinct allele number. Each unique combination of alleles was assigned a distinct sequence type number. The data were used in further analyses. Three lineages, namely Newport-I, Newport-II and Newport-III were identified within serovar Newport which were associated to European humans, animals and humans in North America, respectively. Multidrug resistance phenotypes were most common in Newport-II whereas most isolates in Newport-III were pan-susceptible. When compared to other serovars, the numbers of lineages within Newport were higher than for Enteritidis, Kentucky and Typhimurium but lower than for Paratyphi B. Therefore, serovars of S. enterica subspecies enterica vary greatly in their population structures. The sequence types observed for isolates from chronic human carriers were generally the most common among human-clinical and animal isolates. Most isolates from non-carrier humans plus animals were genetically identical to the carried isolates within most serovars. Genetic diversity was also comparable between isolates from these sources. These results suggest that salmonellae from chronic human carriers belong to the same population as isolates from non-carrier humans and animals. For most serovars, most isolates from reptiles were genetically identical to those from humans or other warm blooded animals. However, in serovars Bovismorbificans, Decatur, Miami and Oranienburg, most reptile isolates were genetically distinct from isolates from other hosts. Only few reptile isolates were tested from Bovismorbificans, Decatur and Miami and only few non-reptile isolates were tested from Oranienburg, and in larger numbers of such isolates would be needed to determine whether these differences are statistically significant.
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Haque, Saif Ahmed. "Charge recombination kinetics in dye sensitised nanocrystalline solar cells." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342251.
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Davies, Matthew John. "Optical studies of InGaN/GaN quantum well structures." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/optical-studies-of-ingangan-quantum-well-structures(f6c6e59b-8366-44aa-b149-9338d3f03dc0).html.
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In this thesis I present and discuss the results of optical spectroscopy performed on InGaN/GaN single and multiple quantum well (QW) structures. I report on the optical properties of InGaN/GaN single and multiple QW structures, measured at high excitation power densities. I show a correlation exists between the reduction in PL efficiency at high excitation power densities, the phenomenon so-called ``efficiency-droop'', and a broadening of the PL spectra. I also show a distinct change in recombination dynamics, measured by time-resolved photoluminescence (PL), which occurs at the excitation power densities for which efficiency droop is measured. The broadening of the PL spectra at high excitation power densities is shown to occur due to a rapidly redshifting, short-lived high energy emission band. The high energy emission band is proposed to be due to the recombination of weakly localised/delocalised carriers occurring as a consequence of the progressive saturation of the local potential fluctuations responsible for carrier localisation, at high excitation power densities. I report on the effects of varying threading dislocation (TD) density on the optical properties of InGaN/GaN multiple QW structures. No systematic relationship exists between the room temperature internal quantum efficiency (IQE) and the TD density, in a series of nominally identical InGaN/GaN multiple QWs deposited on GaN templates of varying TD density. I also show the excitation power density dependence of the PL efficiency, at room temperatures, is unaffected for variation in the TD density between 2 x107 and 5 x109 cm-2. The independence of the optical properties to TD density is proposed to be a consequence of the strong carrier localisation, and hence short carrier diffusion lengths. I report on the effects of including an InGaN underlayer on the optical and microstructural properties of InGaN/GaN multiple QW structures. I show an increase in the room temperature IQE occurs for the structure containing the InGaN underlayer, compared to the reference. I show using PL excitation spectroscopy that an additional carrier transfer and recombination process occurs on the high energy side of the PL spectrum associated with the InGaN underlayer. Using PL decay time measurements I show the additional recombination process for carriers excited in the underlayer occurs on a faster timescale than the recombination at the peak of the PL spectrum. The additional contribution to the spectrum from the faster recombination process is proposed as responsible for the increase in room temperature IQE.
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林, 利彦. "高耐圧パワー半導体素子を目指したp型SiC結晶のキャリア寿命に関する研究." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/174947.
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Vaillant, Frédéric. "Contribution à l'étude du dopage et de la recombinaison dans le silicium amorphe hydrogéné." Grenoble 1, 1987. http://www.theses.fr/1987GRE10058.
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Effet de l'introduction de diborane et de phosphine dans le melange gazeux depose par decharge electroluminescente a 50 h::(3). Caracterisation par methode optique dans le visible et l'ir, deflexion photothermique, conductivite et photoconductivite stationnaire. Variation avec le dopage de proprietes electriques. Proposition d'un nouveau modele de recombinaison
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McBride, Patrick M. "The Effect of Polarization and InGaN Quantum Well Shape in Multiple Quantum Well Light Emitting Diode Heterostructures." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/822.
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Previous research in InGaN/GaN light emitting diodes (LEDs) employing semi-classical drift-diffusion models has used reduced polarization constants without much physical explanantion. This paper investigates possible physical explanations for this effective polarization reduction in InGaN LEDs through the use of the simulation software SiLENSe. One major problem of current LED simulations is the assumption of perfectly discrete transitions between the quantum well (QW) and blocking layers when experiments have shown this to not be the case. The In concentration profile within InGaN multiple quantum well (MQW) devices shows much smoother and delayed transitions indicative of indium diffusion and drift during common atomic deposition techniques (e.g. molecular beam epitaxy, chemical vapor deposition). In this case the InGaN square QW approximation may not be valid in modeling the devices' true electronic behavior. A simulation of a 3QW InGaN/GaN LED heterostructure with an AlGaN electron blocking layer is discussed in this paper. Polarization coefficients were reduced to 70% and 40% empirical values to simulate polarization shielding effects. QW shapes of square (3 nm), trapezoidal, and triangular profiles were used to simulate realistic QW shapes. The J-V characteristic and electron-hole wavefunctions of each device were monitored. Polarization reduction decreased the onset voltage from 4.0 V to 3.0 V while QW size reduction decreased the onset voltage from 4.0 V to 3.5 V. The increased current density in both cases can be attributed to increased wavefunction overlap in the QWs.
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Feix, Felix. "Recombination dynamics in (In,Ga)N/GaN heterostructures: Influence of localization and crystal polarity." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19134.
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(In,Ga)N/GaN-Leuchtdioden wurden vor mehr als 10 Jahren kommerzialisiert, dennoch ist das Verständnis über den Einfluss von Lokalisierung auf die Rekombinationsdynamik in den (In,Ga)N/GaN Quantengräben (QG) unvollständig. In dieser Arbeit nutzen wir die temperaturabhängige stationäre und zeitaufgelöste Spektroskopie der Photolumineszenz (PL), um diesen Einfluss in einer typischen Ga-polaren, planaren (In,Ga)N/GaN-QG-Struktur zu untersuchen. Zusätzlich dehnen wir unsere Studie auf N-polare, axiale (In,Ga)N/GaN Quantumscheiben, nichtpolare Kern/Mantel GaN/(In,Ga)N µ-Drähte und Ga-polare, submonolage InN/GaN Übergitter aus. Während wir einen einfach exponentiellen Abfall der PL-Intensität in den nichtpolaren QG beobachten (Hinweise auf die Rekombination von Exzitonen), folgen die PL-Transienten in polaren QG asymptotisch einem Potenzgesetz. Dieses Potenzgesetz weist auf eine Rekombination zwischen individuell lokalisierten, räumlich getrennten Elektronen und Löchern hin. Für einen solchen Zerfall kann keine eindeutige PL-Lebensdauer definiert werden, was die Schätzung der internen Quanteneffizienz und die Bestimmung einer Diffusionslänge erschwert. Um nützliche Rekombinationsparameter und Diffusivitäten für die polaren QG zu extrahieren, analysieren wir die PL-Transienten mit positionsabhängigen Diffusionsreaktionsgleichungen, die durch einen Monte-Carlo-Algorithmus effizient gelöst werden. Aus diesen Simulationen ergibt sich, dass das asymptotische Potenzgesetz auch bei effizienter nichtstrahlender Rekombination (z. B. in den Nanodrähten) erhalten bleibt. Zudem stellen wir fest, dass sich die InN/GaN Übergitter elektronisch wie konventionelle (In,Ga)N/GaN QG verhalten, aber mit starkem, thermisch aktiviertem nichtstrahlenden Kanal. Des Weiteren zeigen wir, dass das Verhältnis von Lokalisierungs- und Exzitonenbindungsenergie bestimmt, dass die Rekombination entweder durch das Tunneln von Elektronen und Löchern oder durch den Zerfall von Exzitonen dominiert wird.(In,Ga)N/GaN light-emitting diodes have been commercialized more than one decade ago. However, the knowledge about the influence of the localization on the recombination dynamics and on the diffusivity in the (In,Ga)N/GaN quantum wells (QWs) is still incomplete. In this thesis, we employ temperature-dependent steady-state and time-resolved photoluminescence (PL) spectroscopy to investigate the impact of localization on the recombination dynamics of a typical Ga-polar, planar (In,Ga)N/GaN QW structure. In addition, we extend our study to N-polar, axial (In,Ga)N/GaN quantum disks, nonpolar core/shell GaN/(In,Ga)N µ-rods, and Ga-polar, sub-monolayer InN/GaN superlattices. While we observe a single exponential decay of the PL intensity in the nonpolar QWs, indicating the recombination of excitons, the decay of the PL intensity in polar QWs asymptotically obeys a power law. This power law reveals that recombination occurs between individually localized, spatially separated electrons and holes. No unique PL lifetime can be defined for such a decay, which impedes the estimation of the internal quantum efficiency and the determination of a diffusion length. In order to extract useful recombination parameters and diffusivities for the polar QWs, we analyze the PL transients with position-dependent diffusion-reaction equations, efficiently solved by a Monte Carlo algorithm. From these simulations, we conclude that the power law asymptote is preserved despite efficient nonradiative recombination in the nanowires. Moreover, we find that the InN/GaN superlattices behave electronically as conventional (In,Ga)N/GaN QWs, but with a strong, thermally-activated nonradiative channel. Furthermore, we demonstrate that the ratio of localization and exciton binding energy, both of which are influenced by the magnitude of the internal electric fields in the QWs, determines the recombination mechanism to be either dominated by tunneling of electrons and holes or by the decay of excitons.
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Brum, José Antonio. "Etude theorique des proprietes electroniques des heterostructures de semiconducteurs." Paris 7, 1987. http://www.theses.fr/1987PA077006.
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Relations de dispersion des porteurs dans le plan des couches, avec attention particuliere aux sous-bandes de valence issues des extrema gamma ::(8) des materiaux hotes; etude des problemes coulombiens avec resolution du probleme de l'exciton et etude de la raie d'emission associee aux recombinaisons electron-trou piege dans les puits quantiques gaas/algaas. Effets d'un champ electrique longitudinal sur les niveaux d'energie a une et deux particules; interpretations de la stabilite de l'exciton et etude des niveaux d'energie d'impurete et des super reseaux "dents de scie". Etude de la capture des porteurs depuis le continuum vers les etats lies du puits quantique (emission de phonon ou niveau-relais quasidiscret). Niveaux d'energie dans les fils quantiques
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Ni, Xianfeng. "Growth and characterization of non-polar GaN materials and investigation of efficiency droop in InGaN light emitting diodes." VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/2235.
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General lighting with InGaN light emitting diodes (LEDs) as light sources is of particular interest in terms of energy savings and related environmental benefits due to high lighting efficiency, long lifetime, and Hg-free nature. Incandescent and fluorescent light sources are used for general lighting almost everywhere. But their lighting efficiency is very limited: only 20-30 lm/W for incandescent lighting bulb, approximately 100 lm/W for fluorescent lighting. State-of-the-art InGaN LEDs with a luminous efficacy of over 200 lm/W at room temperature have been reported. However, the goal of replacing the incandescent and fluorescent lights with InGaN LEDs is still elusive since their lighting efficiency decreases substantially when the injection current increases beyond certain values (typically 10-50 Acm-2). In order to improve the electroluminescence (EL) performance at high currents for InGaN LEDs, two approaches have been undertaken in this thesis. First, we explored the preparation and characterization of non-polar and semi-polar GaN substrates (including a-plane, m-plane and semi-polar planes). These substrates serve as promising alternatives to the commonly used c-plane, with the benefit of a reduced polarization-induced electric field and therefore higher quantum efficiency. It is demonstrated that LEDs on m-plane GaN substrates have inherently higher EL quantum efficiency and better efficiency retention ability at high injection currents than their c-plane counterparts. Secondly, from a device structure level, we explored the possible origins of the EL efficiency degradation at high currents in InGaN LEDs and investigated the effect of hot electrons on EL of LEDs by varying the barrier height of electron blocking layer. A first-order theoretical model is proposed to explain the effect of electron overflow caused by hot electron transport across the LED active region on LED EL performance. The calculation results are in agreement with experimental observations. Furthermore, a novel structure called a “staircase electron injector” (SEI) is demonstrated to effectively thermalize hot electrons, thereby reducing the reduction of EL efficiency due to electron overflow. The SEI features several InyGa1-yN layers, with their In fraction (y) increasing in a stepwise manner, starting with a low value at the first step near the junction with n-GaN.
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Müllhäuser, Jochen R. "Properties of Zincblende GaN and (In,Ga,Al)N Heterostructures grown by Molecular Beam Epitaxy." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 1999. http://dx.doi.org/10.18452/14382.
Full textAbstract:
Während über hexagonales (alpha) GaN zum ersten Mal 1932 berichtet wurde, gelang erst 1989 die Synthese einer mit Molekularstrahlepitaxie (MBE) auf 3C-SiC epitaktisch gewachsenen, metastabilen kubischen (eta) GaN Schicht. Die vorliegende Arbeit befaßt sich mit der Herstellung der Verbindungen eta-(In,Ga,Al)N mittels RF-Plasma unterstützter MBE auf GaAs(001) und den mikrostrukturellen sowie optischen Eigenschaften dieses neuartigen Materialsystems. Im Vergleich zur hexagonalen bietet die kubische Kristallstruktur auf Grund ihrer höheren Symmetrie potentielle Vorteile für die Anwendung in optischen und elektronischen Bauelementen. Viele wichtige Materialgrößen der kubischen Nitride sind jedoch noch gänzlich unbekannt, da sich die Synthese einkristalliner Schichten als sehr schwierig erweist. Das Ziel dieser Arbeit ist es daher erstens, die technologischen Grenzen der Herstellung von bauelementrelevanten kubischen (In,Ga,Al)N Heterostrukturen auszuweiten und zweitens, einen Beitrag zur Aufklärung der bis dato wenig bekannten optischen und elektronischen Eigenschaften des GaN und der Mischkristalle In GaN zu leisten. Zunächst wird ein optimierter MBE Prozess unter Einsatz einer Plasmaquelle hohen Stickstofflusses vorgestellt, welcher nicht nur die reproduzierbare Epitaxie glatter, einphasiger GaN Nukleationsschichten auf GaAs ermöglicht. Vielmehr können damit auch dicke GaN. Schichten mit glatter Oberflächenmorphologie hergestellt werden, welche die Grundlage komplizierterer eta-(In,Ga,Al)N Strukturen bilden. An einer solchen GaN Schicht mit einer mittleren Rauhigkeit von nur 1.5 nm werden dann temperaturabhängige Reflexions- und Transmissionsmessungen durchgeführt. Zur Auswertung der Daten wird ein numerisches Verfahren entwickelt, welches die Berechnung des kompletten Satzes von optischen Konstanten im Spektralgebiet 2.0 = 0.4 wären grün-gelbe Laserdioden. Zusammenfassung in PostScriptWhile the earliest report on wurtzite (alpha) GaN dates back to 1932, it was not until 1989 that the first epitaxial layer of metastable zincblende (eta) GaN has been synthesized by molecular beam epitaxy (MBE) on a 3C-SiC substrate. The present work focuses on radio frequency (RF) plasma-assisted MBE growth, microstructure, and optical properties of the eta-(In,Ga,Al)N material system on GaAs(001). Due to their higher crystal symmetry, these cubic nitrides are expected to be intrinsically superior for (opto-) electronic applications than the widely employed wurtzite counterparts. Owing to the difficulties of obtaining single-phase crystals, many important material constants are essentially unknown for the cubic nitrides. The aim of this work is therefore, first, to push the technological limits of synthesizing device-relevant zincblende (In,Ga,Al)N heterostructures and, second, to determine the basic optical and electronic properties of GaN as well as to investigate the hardly explored alloy InGaN. An optimized MBE growth process is presented which allows not only the reproducible nucleation of smooth, monocrystalline GaN layers on GaAs using a high-nitrogen-flow RF plasma source. In particular, thick single-phase GaN layers with smooth surface morphology are obtained being a prerequisite for the synthesis of ternary eta-(Ga,In,Al)N structures. Temperature dependent reflectance and transmittance measurements are carried out on such a GaN film having a RMS surface roughness as little as 1.5 nm. A numerical method is developed which allows to extract from these data the complete set of optical constants for photon energies covering the transparent as well as the strongly absorbing spectral range (2.0 -- 3.8 eV). Inhomogeneities in the refractive index leading to finite coherence effects are quantitatively analyzed by means of Monte Carlo simulations. The fundamental band gap EG(T) of GaN is determined for 5 < T < 300 K and the room temperature density of states is investigated. Systematic studies of the band edge photoluminescence (PL) in terms of transition energies, lineshapes, linewidths, and intensities are carried out for both alpha- and GaN as a function of temperature. Average phonon energies and coupling constants, activation energies for thermal broadening and quenching are determined. Excitation density dependent PL measurements are carried out for both phases in order to study the impact of nonradiative recombination processes at 300 K. A recombination model is applied to estimate the internal quantum efficiency, the (non)radiative lifetimes, as well as the ratio of the electron to hole capture coefficients for both polytypes. It is seen that the dominant nonradiative centers in the n-type material investigated act as hole traps which, however, can be saturated at already modest carrier injection rates. In summary, despite large defect densities in GaN due to highly mismatched heteroepitaxy on GaAs, band edge luminescence is observed up to 500 K with intensities comparable to those of state-of-the-art alpha-GaN. For the first time, thick InGaN films are fabricated on which blue and green luminescence can be observed up to 400 K for x=0.17 and x=0.4, respectively. Apart from bulk-like InGaN films, the first coherently strained InGaN/GaN (multi) quantum wells with In contents as high as 50 % and abrupt interfaces are grown. This achievement shows that a ternary alloy can be synthesized in a metastable crystal structure far beyond the miscibility limit of its binary constituents despite the handicap of highly lattice mismatched heteroepitaxy. The well widths of these structures range between 4 and 7 nm and are thus beyond the theoretically expected critical thickness for the strain values observed. It is to be expected that even higher In contents can be reached for film thicknesses below 5 nm. The potential application of such InGaN/GaN multi quantum wells with x >= 0.4 would thus be diode lasers operating in the green-yellow range. abstract in PostScript
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Moroni, Didier. "Etude des proprietes optiques de semi-conducteurs composes iii-v et de puits quantiques par photoluminescence et excitation de la photoluminescence." Paris 6, 1987. http://www.theses.fr/1987PA066540.
Full textAbstract:
Identification des types de recombinaison entre 2 et 300k dans les couches epaisses de gainas et gainp epitaxiees sur leur support respectif inp et gaas. Etude de l'origine de la luminescence et variation en fonction de l'epaisseur du taux de capture des porteurs de la barriere dans les puits quantiques ingaas/inp. Determination du coefficient d'interdiffusion de al et ga aux interfaces dans les puits quantiques gaas/gaalas
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Fernandez, Garrillo Pablo Arturo. "Développement de techniques de microscopie Kelvin hautement résolues et photomodulées pour l'étude de systèmes photovoltaïques." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY031/document.
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Cette thèse propose, décrit et utilise un ensemble de techniques basées sur la microscopie à force atomique sous ultravide pour la cartographie simultanée, à l'échelle nanométrique, de la topographie de surface et des dynamiques temporelles des photo-porteurs. Ainsi, en contrôlant la dépendance du photo-potentiel de surface moyen mesuré par microscopie à force de sonde Kelvin en fonction de la fréquence de répétition d'une source lumineuse externe d'excitation, le dispositif expérimental permet d’accéder aux dynamiques temporelles du photo-potentiel de surface qui, à leur tour, permettent d'étudier les dynamiques des photo-porteurs sur une large gamme d'échantillons. Afin de permettre le processus de nano-imagerie bidimensionnelle, ces mesures sont acquises de manière répétée en enregistrant des courbes spectroscopiques en chaque point d’une grille prédéfinie. En utilisant une procédure d'ajustement mathématique automatique, les dynamiques temporelles des photo-porteurs sont extraites à partir des données expérimentales.Cet ensemble de nouvelles méthodes est utilisé pour l’étude de plusieurs types d'échantillons issus de différentes technologies photovoltaïques telles que des couches minces en silicium poly-cristallin à petits grains, des cellules de troisième génération à nano cristaux de silicium, des cellules photovoltaïques organiques et des cellules à base de matériaux de structure pérovskite. Dans chaque cas, on décrit les processus de recombinaison des photo-porteurs ainsi que leur lien avec la morphologie et la structuration du matériau. Enfin, les aspects techniques de ces nouvelles méthodes d’analyse sont présentés, ainsi que leurs limites, notamment celles concernant l'interprétation des résultatsThis thesis is directed towards the proposition and demonstration of a set of novel advanced atomic force microscopy based techniques under ultra-high vacuum conditions, enabling to map simultaneously the surface topography and the photo-carrier dynamics at the nanometre scale. In fact, by monitoring the dependence of the average surface photo-voltage measured with Kelvin probe force microscopy, as a function of the repetition frequency of a modulated excitation source, we will access the built-up and decay dynamics of the surface photo-voltage response which in turn will allows us to study the photo-carrier dynamics over a wide range of samples. In order to enable the 2-dimensional nano-imaging process, Kelvin probe force microscopy under modulated illumination measurements are acquired repeatedly over each point of a predefined grid area over the sample acquiring a set of spectroscopy curves. Then, using an automatic mathematical fit procedure, spectroscopy curves are translated into pixels of the photo-carrier dynamic time-constant images.Moreover, these set of novel techniques will be used to investigate the surface photo-voltage dynamics in several kinds of photovoltaic samples from different technological branches such as small grain polycrystalline silicon thin films, silicon nanocrystal-based third generation cells, bulk heterojunction donor-acceptor organic photovoltaics and organic-inorganic hybrid perovskite single crystal cells, discussing in each case the photo-carrier recombination process and its relation with the material’s structuration/morphology. Finally, technical aspects of these novel techniques will be discussed as well as their limitations and remaining open question regarding results interpretation
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Liu, Chiou-Hua, and 劉秋華. "Dark-Carrier Recombination in Organic Solar Cells." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/53704920412811558385.
Full textAbstract:
碩士國立清華大學
電子工程研究所
96
The carrier recombination in organic solar cells is investigated by numerical modeling to explore the weak dependence of the open circuit voltage on the workfunction of the electrodes. Two recombination mechanisms are proposed. In ohmic contact with low carrier injection barrier, the photo carriers recombine pre-dominantly with dark carriers diffused from the electrode into the semiconductor and the recombination reduces open circuit voltage as mobility increases. The dark carrier induced recombination is the main limit of the power conversion efficiency for BHJ structure. As the barrier is increased such as Schottky barrier structure, the dark-carrier induced recombination is excluded so that photo-carrier induced recombination can be inhibited by increasing mobility and gives a better performance. As a given semiconductor, with decreased workfunction difference of the electrodes, reduces simultaneously the dark carrier recombination and the flat band voltage.The balance between these two opposite factors give a nearly constant open circuit voltage. Instead of using a Schottky contact, this study demonstrate an ideal bi-layer structure to reduce the dark-carrier induced recombination by separating carrier generation region from electrodes. Hence an improvement of power conversion efficiency over 60% is obtained compared with blending structures.
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Chang, Che-Yu, and 張哲毓. "The carrier recombination of InAs/GaAs quantum dots." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/fvss9a.
Full textAbstract:
碩士國立中山大學
物理學系研究所
106
The purpose of this study is to examine the energy released due to excitation and recombination of single-layered and multi-layered InAs/GaAs quantum dots samples at different conditions. The temperature-dependence and power-dependence photoluminescence and time-resolved photoluminescence for the lifetime of the carriers were measured. In addition, the difference between InAs/GaAs single-layer and multi-layer quantum dots were discussed. At 14K, the peak energy was found to be 1.236eV and the highest lifetime was 2.36ns for InAs/GaAs single-layer ground state, 1.234eV and 1.24ns for InAs/GaAs three-layers quantum dots, and 1.278eV and 1.60ns for InAs/ GaAs eight-layers quantum dots.