Dissertations / Theses: 'Photoconducting'

1

Ferguson, John B. "Transport studies of conducting, semiconducting and photoconducting star polymers." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343144440.

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林思敏 and Sze-man Lillian Lam. "Synthesis and photoconducting properties of molecular and polymeric rhenium diimine complexes." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31243241.

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Lam, Sze-man Lillian. "Synthesis and photoconducting properties of molecular and polymeric rhenium diimine complexes /." Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B2521195x.

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4

Kasai, S., T. Katagiri, J. Takayanagi, K. Kawase, and T. Ouchi. "Reduction of phonon resonant terahertz wave absorption in photoconductive switches using epitaxial layer transfer." American Institite of Physics, 2009. http://hdl.handle.net/2237/12632.

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Mokrinskaya, E. V., L. S. Tonkopieva, S. L. Studzinsky, N. A. Davidenko, I. I. Davidenko, A. A. Ishchenko, and G. P. Grabchuk. "Internal Photoeffect in Films of Poly-N-Epoxypropylcarbazole with High Concentration of Anion Polymethine Dye." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35274.

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Growth of concentration of the anion polymethine dye in the films of poly-N-epoxypropylcarbazole involves increase of quenching of photoluminescence in external electric field as well as appearance of longwave band of the photoluminescence and photoconductivity within visible spectral range. It was ascertained that associates of ionic pairs of the dye arise when the concentration increases. Anomalous for semiconductor materials kinetics of the photocurrent growth and relaxation was observed in the films of these composites: time of the photocurrent growth is much less than the time of its relaxation after the light is switched off. Effect of memory of preliminary illumination with light was observed in the films. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35274

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Petty, David Matthew. "Transient photoconduction in phthalocyanines." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277939.

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Kim, Joong Hyun. "Efficient terahertz photoconductive source." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26608.

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Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Ralph, Stephen; Committee Member: Citrin, David; Committee Member: Cressler, John; Committee Member: Denison, Douglas; Committee Member: Mukhopadhyay,Saibal. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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8

Halls, Jonathan James Michael. "Photoconductive properties of conjugated polymers." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368812.

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9

Li, Di. "Investigation of Terahertz photoconductive antennas." Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526799.

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Terahertz (THz) frequency range usually refers to the electromagnetic spectrum between 100 GHz and 10 THz, which is between the millimetre and infrared regions. THz research has received a lot of attention because of its wide potential applications for such as high-speed wireless communications, medical imaging, remote sensing and security scanning. Photoconductive antenna is the most popular device used to generate and detect THz waves. However, there are still many challenges in this area, for example, how to improve its radiation efficiency and how to increase its directivity to the desired direction. In this dissertation, firstly four methods are proposed to improve the generation efficiency of photoconductive antennas. The first method is to adjust the gap of the photoconductive antenna to an optimum value which is dependent on the input laser power and the material properties of the substrate. The second method is to focus the laser beam on a very small area rather than the whole gap and the generated power can be increased by more than 5 times. The third method is to increase the bias voltage, which can strengthen the photo-induced current. The final method discussed is to use the indentation configuration instead of the conventional dipole shape to enhance the electric field in the gap which can result in about two times stronger power radiation. Secondly a THz hom structure is introduced to improve the directivity and the radiation efficiency of the photoconductive antenna. The conventional photoconductive antenna cannot provide high directivity, but this horn antenna can if it is designed and constructed properly. It consists of two main parts: a photoconductive emitter and a THz conical horn. A computer aided design approach has been adopted, and the simulation results show that the THz conical horn antenna with the proposed feeding structure can radiate more THz power in desired directions than conventional antenna. The directivity of this structure is proved to be 10 dB greater than the conventional photoconductive antennas. It should be pointed out that the THz horn antennas are not the same as the conventional microwave horn antennas. The major difference is on the feeding structure. In addition, the effects of the substrate on THz photoconductive antennas are also investigated theoretically and numerically, some very interesting results are obtained.

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Berkin, J. "Transient photoconduction in amphorous materials." Thesis, University of Abertay Dundee, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328002.

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Shura, Megersa Wodajo. "Photoconductive spectroscopy of GaSb thin films." Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1019937.

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In this study, we have investigated the photo-response of gallium antimonide (GaSb) by measuring the spectral, injection level, as well as the temperature dependence of the steady-state photoconductivity of epitaxial films. By combining the various photo-response measurements with-galvanometric measurements, the effective excess carrier lifetimes could be calculated and described in terms of the various experimental variables considered. From a comparison of the measured and theoretical carrier lifetimes, a clear discrepancy was found for the injection dependent results. This inconsistency between the expected and measured behaviours was resolved using a two-layer model to describe the photo-conductive response of the thin film. In this model, the generation/recombination processes are considered for the bulk as well as for a depleted near-surface region. By combining these two contributions when calculating the total excess photocurrent, the various experimental results could be successfully described. The photo-response measurements revealed that the main contribution to the photocurrent came from the near-surface region, where the bandto- band and Auger recombination transitions are reduced. From the simulation of the injection level dependence of the excess carrier lifetime, some of the near-surface characteristics, such as the position of the surface Fermi-level and the surface recombination velocity, could be determined. In the case of p-type GaSb, the room temperature surface Fermi-level was found to be pinned (290±20) meV above the valence band maximum, whereas the n-type material had a pinning position of (150±20) meV above the valence band maximum. These pinning positions were shown to be independent of the doping density and relatively insensitive to the surface treatments considered. The presence of a near-surface depletion region, as well as the position of the surface Fermi-level, was corroborated by Raman spectroscopy. From a comparison of the phonon mode and the phonon-hole plasmon coupled mode, a surface Fermi-level position of (300 ± 30) meV was deduced for p-type GaSb. Finally, the effect various surface treatments have on the photo-response, and related surface properties, were investigated. Removal of the native oxide (HCl:H2O) followed by sulphur passivation (Na2S:9H2O) results in a slight decrease in the surface Fermi-level position. Aging studies however revealed that the surface characteristics reverted back to the untreated values following a few days in air. Coating the GaSb surfaces with a thin ZnS layer was found to have little effect on the surface potential, resulting only in a slight increase in the near-surface donor density. The sensitivity of the measured photocurrent to surface treatments and changes in the ambient with cooling, further validate the importance of considering the surface potential and the related space-charge when describing the photoconductive response of GaSb thin films.

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Howson, Peter Allen. "Bulk photoconductive high voltage switching techniques." Thesis, University of Brighton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357154.

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13

Delord, Jean-Marie. "Echantillonnage photoconductif de signaux radio-fréquence." Chambéry, 2010. http://www.theses.fr/2010CHAMS026.

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La très grande stabilité des sources lasers impulsionnelles utilisées comme "horloges" optiques permet d'envisager la réalisation de convertisseurs analogique-numériques fonctionnant jusqu'aux radio-fréquences. Dans ce travail nous abordons plus précisément l'étude de l'échantillonnage photoconductif pour le traitement de signaux entre 10 et 20 GHz. L'utilisation de matériau semiconducteur rapide (GaAs épitaxié à basse température) nous permet d'obtenir les bandes passantes requises alors que la propagation du signal microonde est assurée par un guide d'onde métallique déposé sur le substrat semiconducteur. Notre contribution consiste en la modélisation et la compréhension des phénomènes physiques mis en jeu, notamment lors de l'interaction lumière-semiconducteur et de leur impact sur les performances du dispositif. Nous avons pour cela développé plusieurs modèles analytiques de la photocommutation, de l'échantillonnage et de la réponse fréquentielle des échantillonneurs. Finalement une étude fine de l'origine des non-linéarités dans la réponse électrique des échantillonneurs sous éclairement nous a permis de démontrer la possibilité de réaliser des dispositifs présentant une résolution effective de 6 bits à la fréquence de 10 GHz
The great stability of mode locked laser used as optical "clocks" allows the realization of analog to digital converters operating up to radio frequencies. In this work we consider more specifically the study the photoconductive sampling of signais between 10 and 20 GHz. The use of ultra fast semiconductor matériel (low temperature grown GaAs) allows us to obtain the required bandwidth while the signal propagation is achieved by a metallic microwave waveguide deposited on the semiconductor substrats. Our contribution consists in the modeling and understanding of physical phenomena involved, particularly in the lightsemiconductor interaction and their impact on device performance. For that, we have developed several analytical models of photoswitching process, sampling process and frequency response of samplers. Finally, a detailed study of the origin of nonlinearities in the electrical response of the samplers under illumination allowed us to demonstrate the feasibility of devices with an effective resolution of 6 bits at a frequency of 10 GHz

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14

Mason, Graeme. "Test and calibration of the Along Track Scanning Radiometer, a satellite-borne infrared radiometer designed to measure sea surface temperature." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293406.

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15

Wolverson, D. "Optical and electronic properties of disordered semiconductors." Thesis, University of Exeter, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379465.

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Stott, Colin Mark. "Synthesis and photoconduction properties of haloanthanthrone pigments." Thesis, Open University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255409.

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Faulks, Richard Wade. "Development of high performance terahertz photoconductive antennas." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609730.

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18

Chegoor, Prashant. "Optical response of polycrystalline mercuric iodide photoconductive detectors." [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001026.

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19

Khiabani, Neda. "Modelling, design and characterisation of terahertz photoconductive antennas." Thesis, University of Liverpool, 2013. http://livrepository.liverpool.ac.uk/14213/.

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The area of Terahertz (THz) is one of the fastest growing research fields in recent years. THz antennas based upon photoconduction techniques are the most common devices in THz systems. However, the radiated THz power from these devices and the efficiency are very low. Also, different antenna excitation and current generation process in THz antennas, as compared to microwave antennas, requires new analyses approaches. Therefore, the motivation of this thesis is to theoretically establish why the THz antenna is inefficient; from which, general methods to improve the performance of such antennas are explored and validated. These investigations are essential to gain a better understanding of THz photoconductive antenna performance. In this research a new equation for the source conductance of a THz antenna is firstly developed. This is a prerequisite for further antenna radiated power analysis. Next, a new equivalent circuit, modelling the underlying physical behaviour of the device through the use of a lumped-element network, is developed. Through this model, various factors which affect the radiated power and efficiency of the THz photoconductive antenna are examined and compared with measurement results. This model can be applied to maximize the optical-to-THz conversion efficiency. Also, temporal voltage behaviour of the antenna can be predicted more realistically. Furthermore, a computational simulation procedure, solving both optoelectronic and electromagnetic problems, is proposed and validated by measurement results. This approach facilitates prediction of THz photoconductive antenna performance before antenna fabrication. In addition, considering the requirement of high THz power and good SNR devices for various THz applications, a new top loaded THz antenna embedded on a conical horn with the trapezoidal photomixer is proposed. The generation of THz photocurrent, impedance matching and coupling of the THz wave to air (the necessary factors for power enhancement) are improved. Moreover, the new trapezoidal photomixer is examined and the measurement results show that it has better radiated THz power and SNR than the bare gap and rectangular photomixers.

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20

Wojtyk, James Taras Ché. "Studies of organic photochromic and photoconductive dye molecules." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0005/NQ42989.pdf.

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21

Baker, C. "Development of semiconductor materials for Terahertz photoconductive antennas." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596274.

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Pulsed terahertz (THz) systems for spectroscopy and imaging are traditionally based on Ti:Sapphire femtosecond laser excitation, with low-temperature (LT)-GaAs photoconductive devices. A number of designs of GaAs photoconductive antennae were characterised in this thesis using 800 nm laser excitation. The THz power emitted was investigated as a function of specific antenna geometry, laser excitation position, laser power, and applied bias. The electric field profile of the devices under bias was investigated by electron beam induced current. These measurements give an indication of the device electric field profile, and can be applied to both pulsed and continuous-wave THz (cw-THz) antennas. There are, however, considerable advantages in moving to longer wavelength excitation. These include a step towards the optimum wavelengths for fibre-optic laser delivery, and potential reductions in the cost of the laser technology. In this thesis, the operation of a pulsed THz imaging system that uses, for the first time, a 1.06 mm femtosecond laser, and photoconductive devices fabricated from LT-In_0.3Ga_0.7As is demonstrated. Biological and non-biological images are presented to show the many potential applications of THz radiation, and the technology compared to existing 800 nm based systems. It is found that ex-situ post growth annealing plays a critical role in determining the properties of LT-InGaAs, and that material with a sub-500 fs carrier lifetime, and superior resistivity can be obtained. The dependence of the carrier lifetime and resistivity on growth and anneal temperature are discussed in detail. To characterise the material, x-ray diffraction is used to identify the presence of defects or traps. Time-resolved photoreflectance shows how the carrier lifetime varies, and electrical measurements are used to give the resistivity of the material. It was demonstrated that upon a mid-temperature anneal (400-600°C) the carrier lifetime actually falls, whilst the resistivity increases.

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22

Wainwright, M. "New photoconductive polymers based on poly(N-vinylcarbazole)." Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382880.

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Klingshim, Christopher J. "Infrared photoconductive PbTe film processing and oxygen sensitization." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98614.

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Thesis: S.B. in Materials Science and Engineering, Massachusetts Institute of Technology, Department of Physics, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 33-34).
Infrared (IR) thermal detectors and photodetectors have significant applications including thermal imaging, infrared spectroscopy and chemical and biological sensing. In this work we focus on photodetectors, which typically use narrow gap semiconductor materials requiring cryogenic cooling to provide measurable signals above thermally generated noise. Our study investigates one class of photodetectors, namely photoconductive semiconductor films. When embedded within resonant cavities, these films are additionally capable of precise detection at narrow, selectable bands and enable the development of monolithically-integrated detectors that are physically small, highly responsive and able to record data autonomously. Lead chalcogenides such as PbTe are ideal photoconductive material candidates because (i) low-cost thermal deposition produces polycrystalline films that exhibit good mid-IR responsivity without being subject to lattice-matching constraints, and (ii) they do not require cryogenic cooling. We show that the responsivity of polycrystalline PbTe is enhanced by oxidation annealing. This investigation sought to determine a viable set of processing conditions for thermally depositing oxygen-sensitized PbTe photoconductors on Si substrates. Depositions were performed under high vacuum on the order of 1 0-6 Torr. Physical shadow-mask and photolithographic techniques were used to pattern the films in order to produce photoconductive samples with varied film and electrical contact geometries. The introduction of non-functional "dummy layers" within 100-300 pm of the usable samples prevented undesired film peeling during the lift-off process. PbTe films displayed an FCC rocksalt structure and slight preference for (200) texture when thermally deposited on a Si substrate. A 250-nm thick sample exhibited large photoconductivity, with responsivity higher than 100 V/W between 2-3 [mu]m wavelengths, a factor of 4 higher than literature values for similar films. Sn metal formed highly ohmic contacts with the PbTe layer, permitting Hall experiments that showed the film to be p-type with a carrier concentration of 1.49 x 1017 cm-3 and Hall mobility of 21 cm 2 V-1 s-. The carrier concentration was thermally activated with activation energy of 0.137 eV. These values are comparable to past experiments in which the film was sensitized by exposure to oxygen at ambient conditions. Further research is needed to establish the exact origin of the enhanced photoconductivity observed.
by Christopher J. Klingshim.
S.B. in Materials Science and Engineering

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24

Ezdi, Kamran [Verfasser]. "Analysis and Simulation of Photoconductive Terahertz Antennas / Kamran Ezdi." Aachen : Shaker, 2011. http://d-nb.info/1074088115/34.

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25

Lourenco, Manon d'Assuncao. "Evaluation of SIMOX substrates using photoconductive frequency resolved spectroscopy." Thesis, University of Surrey, 1991. http://epubs.surrey.ac.uk/776189/.

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26

Zhang, Yi. "Modelling of photoconductive switches in high voltage power applications." Thesis, University of Brighton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239720.

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27

Stone, Michael Raymond. "Photoconductive emitters for pulsed and continuous-wave terahertz generation." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417735.

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28

Hodge, Clifford Charles. "Photoconductive and induced absorption studies of novel semiconductor superlattices." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46342.

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29

Gunda, Rahul. "Performance analysis of high power photoconductive switch at elevated temperature." Diss., Columbia, Mo. : University of Missouri-Columbia, 2005. http://hdl.handle.net/10355/4310.

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Thesis (M.S.)--University of Missouri-Columbia, 2005.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (July 13, 2006) Includes bibliographical references.

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30

Kim, Dae Sin. "Monte Carlo Modeling of Carrier Dynamics in Photoconductive Terahertz Sources." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11526.

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Carrier dynamics in GaAs-based photoconductive terahertz (THz) sources is investigated using Monte Carlo techniques to optimize the emitted THz transients. A self-consistent Monte Carlo-Poisson solver is developed for the spatio-temporal carrier transport properties. The screening contributions to the THz radiation associated with the Coulomb and radiation fields are obtained self-consistently by incorporating the three-dimensional Maxwell equations into the solver. In addition, the enhancement of THz emission by a large trap-enhance field (TEF) near the anode in semi-insulating (SI) photoconductors is investigated. The transport properties of the photoexcited carriers in photoconductive THz sources depend markedly on the initial spatial distribution of those carriers. Thus, considerable control of the emitted THz spectrum can be attained by judiciously choosing the optical excitation spot shape on the photoconductor, since the carrier dynamics that provide the source of the THz radiation are strongly affected by the ensuing screenings. The screening contributions due to the Coulomb and radiation parts of the electromagnetic field acting back on the carrier dynamics are distinguished. The dominant component of the screening field crosses over at an excitation aperture size with full width at half maximum (FWHM) of ~100 um for a range of reasonable excitation levels. In addition, the key mechanisms responsible for the TEF near the anode of SI photoconductors are elucidated in detail. For a given optical excitation power, an enhancement of THz radiation power can be obtained using a maximally broadened excitation aperture in the TEF area elongated along the anode due to the reduction in the Coulomb and radiation screening of the TEF.

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Saeedkia, Daryoosh. "Modeling and Design of Photoconductive and Superconductive Terahertz Photomixer Sources." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/806.

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Terahertz technology is a fast growing field with variety of applications in biology and medicine, medical imaging, material spectroscopy and sensing, monitoring and spectroscopy in pharmaceutical industry, security, and high-data-rate short-range communications. Among different terahertz sources, photomixers are potentially compact, low power consuming, coherent, low-cost, and tunable continuous-wave sources. A terahertz photomixer is a heterodyne scheme, in which two laser beams with their frequency difference falling in the terahertz range mix in a nonlinear medium, such as a photoconductor or a superconductor, and generate a signal, whose frequency is equal to the frequency difference of the two lasers. The frequency of the generated terahertz signal can be tuned by tuning the central frequency of one of the lasers.

In this dissertation, the photomixing in superconductors and photoconductors is studied, and comprehensive analytical models for the interaction of two interfering laser beams with these materials are developed. Integrated photomixer-antenna elements as efficient terahertz sources are introduced and arrays of these elements as high power terahertz sources are designed. Also, an array of photoconductive photomixer-antenna elements with integrated excitation scheme is proposed.

In a photo-excited superconductor, the fundamental equations for the motion of the carriers inside the superconductor material are used in connection with the two-temperature model to find an analytic expression for the generated terahertz photocurrent inside the film. In a photo-excited photoconductor, the continuity equations for the electron and hole densities are solved in their general form along with the appropriate boundary conditions to find photocurrent distribution inside the photoconductor film. It is shown that in a continuous-wave (CW) terahertz photomixing scheme, the resulting photocurrent contains a dc component and a terahertz traveling-wave component. The dependency of the amplitude and the phase of the generated photocurrent on the physical parameters of the photomixer, the parameters of the lasers, the applied dc bias, and the configuration of the device is explored in detail for a photoconductive photomixer made of low-temperature grown (LTG) GaAs and for a high-temperature superconductive photomixer made of YBa₂Cu₃O_7-δ.

The developed models for the photoconductive and the superconductive terahertz photomixers are used to design new integrated photomixer-antenna devices. In these devices, the photomixing film simultaneously acts as an efficient radiator at the terahertz frequencies. Integrating the photomixing medium with the antenna not only eliminates any source to antenna coupling problem, but also makes the proposed device attractive for array configurations.

To increase the generated terahertz power, arrays of the photoconductive and the superconductive photomixer-antenna elements are proposed as CW terahertz sources. It is shown that a sub-milliwatt terahertz power is achievable from a typical superconductive photomixer-antenna array structure. The beam steering capability of the proposed devices is also investigated.

A photoconductive photomixer-antenna array with integrated excitation scheme is proposed, in which the laser beams are guided inside the substrate and excite the photomixer elements. In this way the laser power is only being consumed by the photomixer elements, and the photomixer-antenna elements can be integrated with other optical components on a single substrate. The whole structure is robust and less sensitive to vibration and other environmental parameters.

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Su, Hansheng. "Development of optically controlled FSS and antenna using photoconductive approach." Thesis, Queen Mary, University of London, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610933.

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33

Abdul-Niby, Mohammed. "Photoconductive frequency resolved spectroscopy for hydrogen and helium implanted silicon." Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/804439/.

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34

Kowalczuk, Emma K. "Simulating, fabricating and characterising photoconductive microwave switches for RF applications." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/14968.

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Photoconductive microwave switches can be used in place of traditional microwave switches to reconfigure antennas and RF circuits. The switch, which consists of a silicon die placed over a gap in transmission line, is controlled by illumination via a fibre optic cable. Hence there is no requirement to design electrical biasing lines which may affect RF performance. This benefit is the main motivation behind further developing and understanding the photoconductive switch. The second motivation is the growing demand for reconfigurable antennas which necessitate certain switching requirements; one specific area of interest is in cognitive radio applications. However, in order to use such a switch in RF circuitry, the photoconductive nature of the switch must be understood. This is addressed in this thesis presenting and applying analytical equations which dictate the material properties in photoconductive silicon. These equations are then used to generate a 3D EM simulation model to investigate transmission loss in the photoconductive switch. The concept of signal planarity is investigated so as to give some insight into the best way to package the switch. In order to potentially reduce loss and facilitate a packaged device, the fabrication of the switch is investigated. Namely, the treatment of the silicon and the addition of contacts on the silicon are discussed as possible methods to improve switch performance. Lastly, linearity, power handing and switching times are presented for the photoconductive switch. This characterisation is important with regards to understanding which types of application the switch can be used in. In particular the single tone and two tone linearity of the switch is measured these values have not previously been reported for this type of photoconductive switch. The results are encouraging and support further development of the switch into a packaged product to be used in reconfigurable antennas and circuitry.

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35

Ariaudo, Myriam. "Analyse théorique de la génération optoélectronique d'impulsions ultrabrèves par photoconduction." Limoges, 1996. http://www.theses.fr/1996LIMO0049.

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Les travaux de recherche presentes dans ce memoire traitent de l'analyse de la generation d'impulsions electromagnetiques ultracourtes par phenomene de photoconduction. L'utilisation grandissante de ces signaux dans des dispositifs optoelectroniques, tels qu'un interrupteur, un echantillonneur ou un autocorrelateur, necessite une connaissance et une maitrise des phenomenes physiques intervenant lors de l'interaction laser/matiere. L'outil numerique developpe est base sur la resolution des equations de maxwell et des equations des semiconducteurs par la methode des differences finies dans le domaine temporel. Les phenomenes optiques sont ainsi couples aux phenomenes electromagnetiques. Une premiere application de cet outil numerique consiste a connaitre l'influence des parametres physiques et geometriques sur la forme et l'amplitude du courant photogenere. Une deuxieme application permet de determiner les caracteristiques du materiau etudie par la modelisation d'un autocorrelateur en liaison avec l'experimentation

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36

IVERSON, ARTHUR EVAN. "THE MATHEMATICAL MODELING OF TIME-DEPENDENT PHOTOCONDUCTIVE PHENOMENA IN SEMICONDUCTORS." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184068.

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This dissertation presents results pertaining to the mathematical modeling of semiconductor photoconductors and includes the formulation, analysis, and solution of photoconductive device model equations. The fundamental semiconductor device equations of continuity and transport are derived for the case of a material which contains a large density of deep-level impurities. Electron and hole trapping on deep-level impurities is accounted for by trapping-kinetics rate equations. The coupling between carrier drift and the electric field is completed through Poisson's equation. Simple, nonlinear model equations are presented for bulk-material response based on the dynamics of electron and hole trapping and recombination on deep-level impurities. The characteristics of the solution to these model equations are observed to depend strongly on the excitation intensity. These model equations qualitatively reproduce observed experimental behavior of an iron-doped indium phosphide photoconductor. A theory of the effect of deep-level centers on the generation-recombination noise and responsivity of an intrinsic photoconductor is presented. It is shown that the deep-level centers can influence the generation-recombination noise and responsivity in three main ways: (i) they can shorten the bulk carrier lifetime by Schockley-Read-Hall recombination; (ii) for some values of the capture cross sections, deep-level densities, and temperature, the deep-level centers can trap a significant fraction of the photogenerated minority carriers. This trapping reduces the effective minority carrier mobility and diffusivity and thus reduces the effect of carrier sweep out on both generation noise and responsivity; (iii) the deep-level centers add a new thermal noise source, which results from fluctuations between bound and free carriers. The strength of this new noise source decreases with decreasing temperature at a slower rate than band-to-band thermal generation-recombination noise. Photoconductive device model equations based on time-dependent, convective/diffusive transport equations are presented. The system of model equations is solved numerically with boundary conditions that represent ideal ohmic contacts. Computed results are presented for different photoconductor lengths and bias voltages with spatially uniform, rectangular light-pulse illumination.

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37

Huang, Chih-Jung. "Opto-electronic class AB microwave power amplifier using photoconductive switch technology." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4458.

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Thesis (Ph.D.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (April 26, 2007) Vita. Includes bibliographical references.

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38

Kelkar, Kapil S. "Silicon carbide as a photoconductive switch material for high power applications." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4469.

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Thesis (Ph. D.) University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 3, 2007) Includes bibliographical references.

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39

Vu, Nhan Trung. "Characterisation of cadmium selenide material for high speed photoconductive switching systems." Thesis, University of Brighton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310102.

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40

O'Callaghan, Gregory Calum. "The serendipitous discovery of luminescent and liquid crystalline and photoconductive triphenoxazoles." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7845/.

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Triphenylene has been shown to possess interesting luminescent properties, such as a large pseudo Stokes shift and an excellent molar absorptivity coefficient. The research described in this thesis aims to focus on the serendipitous discovery of the incorporation of an oxazole moiety to the triphenylene core of alkoxytriphenylenes , and the study of the properties of this new class of material - triphenoxazole s- which show them to be highly luminescent, photoconducting and liquid crystalline . The thesis mainly focuses upon two series of alkoxytriphenoxazoles. 1) where the effects of incorporating \(ortho\), \(meta\) and \(para\) fluorophenyl as the oxazole R group of the triphenoxazole derivatives. Where it is shown that a change in position of the fluorine leads to significant alterations in the fluorescent and liquid crystal properties. 2) The effects of increasing the aromatic area of the oxazole R group from phenyl to anthracyl. Whereby fluorescence is significantly red shifted and the Col\(_h\) mesophase is extended to > 100 °C. Furthermore , initial photoconductivity tests showed the triphenoxazole to be significantly more photoconductive than the alkoxy parent compound.

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41

Reynolds, Gillian Althea Maria. "Electronic transport and photoconductive properties of resorcinol-formaldehyde-based carbon aerogels." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/39370.

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42

Paslaski, Joel Yariv Amnon Yariv Amnon. "High speed optoelectronics : photodiodes, Q-switched laser diode and photoconductive sampling /." Diss., Pasadena, Calif. : California Institute of Technology, 1990. http://resolver.caltech.edu/CaltechETD:etd-05092007-084117.

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43

Abdulmunem, Oday Mazin [Verfasser], and Martin [Akademischer Betreuer] Koch. "New Materials for Photoconductive Terahertz Antennas / Oday Mazin Abdulmunem ; Betreuer: Martin Koch." Marburg : Philipps-Universität Marburg, 2017. http://d-nb.info/114312488X/34.

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44

DE, CARRE PATRICE. "Etude experimentale des proprietes de transport non stationnaire dans inp par photoconduction." Paris 11, 1990. http://www.theses.fr/1990PA112124.

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Le developpement de l'electronique rapide et de l'optoelectronique est associe a celui des semiconducteurs composes iii-v, dont inp. Ce travail porte sur l'etude experimentale des phenomenes de transport non stationnaire dans inp, par mesure de photocourant en regime permanent d'eclairement, sur des dispositifs semiconducteurs submicroniques de differentes longueurs. L'interpretation des resultats fait appel a des simulations numeriques de type monte-carlo. La structure de bande d'inp et les mecanismes d'interactions entre electrons et reseau cristallin sont decrits et permettent d'analyser les caracteristiques de transport electronique stationnaire et non stationnaire obtenues a l'aide de simulations numeriques. Les caracteristiques de transport dans inp sont comparees a celles obtenues dans gaas. La methode de photoconduction employee permet de s'affranchir des effets geometriques lies a la structure planaire des dispositifs et, en ne mesurant que des photocourants faibles devant le courant d'obscurite, d'une eventuelle non-linearite des contacts. La vitesse moyenne des porteurs peut alors etre deduite d'une mesure du photocourant en regime permanent d'eclairement lorsqu'une bonne reproductibilite des conditions d'eclairement est assuree. Les phenomenes de diffraction de la lumiere par la fente epaisse formee par l'espace interelectrode sont mis en evidence et l'estimation des coefficients de transmission de la lumiere est validee experimentalement. La caracterisation des echantillons faite en obscurite, sous eclairement et sous champ magnetique a permis de determiner la mobilite dans les couches epitaxiees et sous la surface ainsi que le dopage residuel des couches. A 300 k et 77 k, les caracteristiques donnant les variations du photocourant en fonction du champ electrique applique montrent sous certaines conditions experimentales, l'existence du phenomene de survitesse sur des longueurs s

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45

Haristoy, Denis. "Synthese, mesomorphisme et proprietes de photoconduction de cristaux liquides de type calamitique." Université Louis Pasteur (Strasbourg) (1971-2008), 2000. http://www.theses.fr/2000STR13167.

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Quatre differents types de mesogenes calamitiques comportant des curs rigides heteroaromatiques soufres ont ete synthetises. La substitution de ces curs par certaines natures de chaines a permis d'abaisser avec succes les temperatures de transition de phases. Les proprietes mesomorphes ont ete systematiquement caracterisees par microscopie optique en lumiere polarisee, analyse enthalpique differentielle et diffraction des rayons x. Ces analyses ont notamment permis de mettre en evidence pour un type de composes, une mesophase originale de type lamello-colonnaire pour laquelle nous avons propose deux modeles d'organisation moleculaires. Le comportement photoconducteur de ces systemes mesomorphes a tout d'abord ete verifie a partir de la detection du photocourant. La presence d'un photocourant particulierement net a ete obtenu dans le cas du compose presentant la phase lamello-colonnaire. Pour ce derive, la nature du photocourant a ensuite ete examinee de maniere plus approfondie par la technique du temps de vol. Des fortes valeurs de mobilite de l'ordre de 5. 10 3 cm 2. V 1. S 1 ont alors ete mises en evidence pour un transport de trous et d'electrons. Ces resultats attestent le caractere a la fois electronique et ambipolaire du photocourant observe dans ce compose. Les liens possibles entre les potentiels moleculaires et la photoconduction ont egalement ete examines. L'importance des faibles valeurs de potentiels d'ionisation a alors ete mise en evidence pour la photoconduction par trou. Deux techniques de determination des potentiels d'ionisation (par calculs moleculaires et par mesures de voltamperometrie cyclique) ont ensuite ete utilisees pour definir leurs limites de validite ; ceci dans le but d'exploiter ces techniques comme outils dans la selection de futurs systemes photoconducteurs.

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46

Abdulmunem, Oday M. [Verfasser], and Martin [Akademischer Betreuer] Koch. "New Materials for Photoconductive Terahertz Antennas / Oday Mazin Abdulmunem ; Betreuer: Martin Koch." Marburg : Philipps-Universität Marburg, 2017. http://d-nb.info/114312488X/34.

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47

Gambaryan, K. M., V. G. Harutyunyan, V. M. Aroutiounian, T. Boeck, O. Marquardt, and F. Schuette. "InAsSbP-based Quantum Dot Mid-Infrared Photodetectors: Fabrication, Properties and Applications." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35354.

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The mid-infrared photoconductive cells (PCC) made of n-InAs(100) crystals with InAsSbP quantum dots (QDs) on the PCC surface, as well as InAsSbP-based diode heterostructures with QDs on epilayer–substrate interface are reported. Both QDs-based semiconductor structures are considered as attractive devices for several mid-infrared applications. The liquid phase epitaxy, AFM, TEM and STM techniques are utilized for the growth of QDs and epitaxial cap layers and their characterization, respectively. Anoma-lous photovoltaic effect is detected in PCC with type-II QDs. The open-circuit voltage and short-circuit cur-rent are measured versus radiation power density of the He-Ne laser at λ 3.39, 1.15 and 0.63 μm wave-lengths. The formation of QDs leads to the increasing of the PCC’s sheet resistance up to one order and re-sults in red shift of the photoresponse spectrum. The QDs-based PCC’s voltage and current responsivity at room temperature are equal to 1.5 V/W and 82 mA/W, respectively, at zero bias and λ 3.39 μm. The main peak at 3.48 μm and additional peaks at 2.6 μm and 2.85 μm wavelengths revealed on QDs-based devices’ photoresponse and luminescence spectra allow to fabricate optical gas sensors, in particularly, for the me-thane, water vapor and carbon dioxide detection. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35354

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48

Erozbek, Gungor Ummugul. "Development Of A Compact Time-domain Terahertz Spectrometer Using Photoconductive Antenna Detection Method." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610440/index.pdf.

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In this thesis, we describe the development of a time-domain terahertz (THz) spectrometer driven by two different laser sources: an Er-doped femtosecond fiber laser and a mode-locked Ti:Sapphire laser. The resulting THz electromagnetic radiation was generated and detected using photoconductive antenna detection methods in both systems. In these experiments we characterized the THz power output for both the fiber laser driven system and the Ti:Sapphire laser driven system. Emphasis is given throughout this thesis on understanding the working principles behind time-domain terahertz spectroscopy, applications of THz radiation and terahertz generation as well as terahertz detection methods. We calculated the THz power output using two different methods. By using the &ldquo
Hertzian Dipole&rdquo
method we estimated the generated THz power after the generation photoconductive antenna. Using this method, we showed that the v generated power is on the order of milliwatts, which is far larger than the expected power typical for these systems. The second, &ldquo
Open-Circuit Voltage&rdquo
method, allowed us to calculate the received power on the detection photoconductive antenna. Using this method we were able to show that the THz power generated and detected in these systems is on the order of microwatts. For the mode-locked fiber laser driven spectrometer we obtained on average a ~ 4 ps (0.25 THz) pulse length which corresponded to an average power in the range of 71.8 nW - 70.54 &
#956
W on a dipole antenna with a 6 &
#956
m dipole gap and 44 &
#956
m dipole length. Using the mode-locked Ti:Sapphire laser driven spectrometer we observed a ~ 2 ps (0.5 THz) pulse length and average power in the range of 0.54 nW &ndash
5.12 &
#956
W on a different dipole antenna with a 5 &
#956
m gap and 40 &
#956
m dipole length. Since these values agree with expected values for these systems we believe the &ldquo
Open-Circuit Voltage&rdquo
method is appropriate when trying to calculate the THz power.

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49

Kaczmarek, Jean. "Mise en évidence des phénomènes de photoconduction dans des cristaux liquides ferroélectriques photosensibles." Thesis, Lille, 2018. http://www.theses.fr/2018LIL1R028.

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Les cristaux liquides ferroélectriques (CLF), photosensibles, sont susceptibles de générer des charges de surfaces s’ils sont soumis à un champ électrique ; cette propriété est mise à profit dans les dispositifs d’affichages à cadence rapide. Les CLF utilisés dans ce travail présentent une phase smectique C* ferroélectrique ; l’un est un mélange commercial utilisé comme matériau hôte, l’autre, un dérivé azobenzénique photosensible utilisé comme dopant (1, 3, 5%). Les propriétés optiques et ferroélectriques ont été étudiées en fonction de la concentration, de la température et du champ électrique, sans et sous illumination UV (à 365 nm) en phase SmC* ; le dopage et l’illumination engendrent la réduction de l’ordre smectique ; l’illumination UV induit la photo-isomérisation Trans-Cis, la polarisation spontanée diminue avec l’ajout de dopant et l’illumination UV. Des mesures du temps de vol des charges (trous/électrons) photogénérées par impulsion laser- technique développée au laboratoire par ce travail – mettent en évidence un photocourant de type dispersif et ambipolaire, dont l’intensité varie avec le champ électrique et la température. L’influence du champ interne propre à la phase SmC se traduit sur le photocourant par le passage d’intensités négatives vers des intensités positives pour les trous et pour les électrons. Les trous présentent des valeurs de mobilités plus élevées que les électrons. Le mécanisme de conduction, déduit des modèles d’Arrhénius et de Bassler, est un déplacement de charge par sauts successifs entre molécules voisines. Pour les mélanges, le dopant réduit le temps de transit des charges et conduit à des valeurs de mobilités élevées et constantes avec la température ; le dopant agit en renforçant la cohésion des couches smectiques, et réduit la viscosité du mélange. En configuration Cis le signal conserve son caractère ambipolaire et dispersif mais tend à s’atténuer avec le dopage et à disparaître sous UV
Ferroelectrical materials possess the remarkable property to orienting themselves and generating surfaces charges under electric field. Dipole movements can be observed by measuring internal electric field or spontaneous polarization under alternative electric field. These organic materials are widely used in fast display devices. The aim of this work was to propose a direct current measurement of photoconduction phenomenon in ferroelectric non-photosensitive and photosensitive liquid crystals by charge carrier transport in SSFLC devices using time of flight methodology. The proposed method is based on charge carrier transport determination which providing access to characteristics parameters like mobility. Differentprocedures have been presented for mobility estimation from adding increasing dopant concentrations, electrical field and temperature, as well as charge behaviour pattern for exploitation and description. This materials show real influence of several parameters on the photocurrent shape signal and different mobility values under large scales of temperature. The validation of the method on photosensitive ferroelectric materials and obtained results by data treatment show that this method can be used to characterize another liquid crystal whatever its phase including SmC*

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50

Haddab, Karima. "Propriétés électroniques du silicium amorphe hydrogéné : courants limités par charge d'espace et photoconduction." Paris 11, 1988. http://www.theses.fr/1988PA112052.

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Les propriétés électroniques du silicium amorphe hydrogène sont déterminés par la densité d’états dans la bande interdite. A partir de la méthode des courants limités par charge d’espace (CLCE) sous excitation lumineuse, nous avons pu déterminer cette densité d’états dans un domaine d’énergie situé au-dessus du niveau de Fermi. Nous avons obtenu une densité d’états exponentielle de température caractéristique de l’order de 1000k. Nous proposons une discussion sur la différence dans les pentes de densité d’états déterminées à partir de la méthode précédente, de la méthode CLCE à l’obscurité et à partir des mesures de photoconductivité. Dans une deuxième partie nous avons fait des mesures de rendement et du temps de réponse de la photoconductivité dans un large domaine de flux. La comparaison du rapport d’électrons piégés aux électrons libres obtenu expérimentalement avec le même rapport obtenu à partir d’un calcul a permis de montrer la validité des densités d’états obtenues par CLCE sous excitation lumineuse.

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Dissertations / Theses on the topic 'Photoconducting'

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