Dissertations / Theses on the topic 'Impurity doping'

GaN has the potential to revolutionize the high power electronics industry, enabling high voltage applications and better power conversion efficiency due to its intrinsic material properties and newly available high purity bulk substrates. However, unintentional impurity incorporation needs to be reduced. This reduction can be accomplished by reducing the source of contamination and exploration of extreme growth conditions which reduce the incorporation of these contaminants. Newly available bulk substrates with low threading dislocations allow for better study of material properties, as opposed to material whose properties are dominated by structural and chemical defects. In addition, very thick films can be grown without cracking due to exact lattice and thermal expansion coefficient match. Through chemical and electrical measurements, this work aims to find growth conditions which reduces contamination without a severe impact on growth rate, which is an important factor from an industry standpoint. The proposed thicknesses of these devices are on the order of one hundred microns and requires tight control of the intentional dopants.
Doctor of Philosophy
GaN is a compound semiconductor which has the potential to revolutionize the high power electronics industry, enabling new applications and energy savings due to its inherent material properties. However, material quality and purity requires improvement. This improvement can be accomplished by reducing contamination and growing under extreme conditions. Newly available bulk substrates with low defects allow for better study of material properties. In addition, very thick films can be grown without cracking on these substrates due to exact lattice and thermal expansion coefficient match. Through chemical and electrical measurements, this work aims to find optimal growth conditions for high purity GaN without a severe impact on growth rate, which is an important factor from an industry standpoint. The proposed thicknesses of these devices are on the order of one hundred microns and requires tight control of impurities.

CdTe/CdS thin film solar cells are the most promising cost-effective solar cells. The goal of this project is to improve the performance for CdS/CdTe devices by improving the open circuit voltage Voc and current density Jsc. Efforts focused on increasing the Voc, which include increasing the doping concentration by introducing Phosphorus and Antimony, finding and testing new back contact materials, and varying the ambient of CSS CdTe. In addition, the effect of Zn2SnO4 on the cells' performance was also studied. Electrical characterization of the thin films and completed devices were carried out by Current-Voltage (J-V), Capacitance-Voltage (C-V), and Spectral Response (SR) measurements. Structural/chemical characterization was done by SEM, XRD and EDS analysis. The ambient of CSS CdTe affects the growth rate, the grain size and electronic properties of CdTe. The N2/O2 mixture with varied ratio (N2/O2=9/1, 7/3, 5/5 and 1/9) was used in this study. The cells' performance and the net carrier concentration were studied as a function of the N2/O2 ratio. The net carrier concentration increases with the increasing O2 concentration. The extrinsic impurities (P and Sb) were incorporated into CdTe layer. Phosphorus was directly introduced into CSS CdTe source. The Sb was incorporated into CdTe by a diffusion process. The effects of the annealing parameters, the excess Sb on CdTe surface, the CdCl2 treatment and the depth of Sb in CdTe were studied. Higher doping concentration up to 1016 cm-3 has been achieved, however, Voc is still in the range of 830 mV.

Electron scattering by a single or multiple impurities affects the quantizaton of conductance of a semiconductor nanochannel. The theoretical model of electron transport in a hardwall nanostructure with an impurity requires an analysis of the electronic transverse energy levels, eigenfunctions and hopping integrals resulting from cross channel or transverse confinement. Theoretical equations for the electronic transverse energy levels, wavefunctions and hopping integrals in the case of a repulsive, finite strength rectangular barrier arbitrarily positioned in the nanochannel are presented. The effects of size, strength and location of the impurity are discussed.In order to find the electronic transverse energy levels, wavefunctions and hopping integrals, two FORTRAN computer programs were developed. The first, called Program Data Input, writes the computational parameters to a data file. The second, Program Single Impurity, uses this data file in performing the calculations of the electronic transverse energy levels, eigenfunctions and hopping integrals.
Department of Physics and Astronomy

I nanocristalli colloidali a semiconduttore (NC), grazie alle loro proprietà ottiche regolabili tramite la dimensione ed alla processabilità in soluzione, sono state a lungo proposte come alternative versatili e sintetizzate chimicamente per numerose tecnologie fotoniche, optoelettroniche e quanto-computazionali, nonché come building-blocks funzionali e superatomici per metamateriali artificiali assemblati con approcci bottom-up. Dalla loro scoperta oltre 30 anni fa, enormi progressi nella chimica colloidale e superficiale, nella fisica dei NC e nelle applicazioni nei dispostivi, hanno portato queste proposte sempre più vicine alla realtà. In questo lavoro esploro i fenomeni fotofisici di quattro diversi sistemi di NC, differenziati dalla composizione chimica e dalla loro forma. Ho studiato i più promettenti NC ternari intrinseci di CuInS2 che in modo innato offrono alternative senza metalli pesanti e non tossiche ai materiali esistenti a base di Cd e Pb, caratterizzate da un ampio Stokes shift e lunghi tempi di decadimento di fotoluminescenza. L’origine di queste proprietà ottiche nei NC di CuInS2 non era però stata compresa, con teorie contrastanti che le descrivono. Qui, dopo aver confermato sperimentalmente l’origine della PL dovuta alla struttura fine della banda di valenza, abbiamo ottimizzato i NC per fabbricare un concentratore solare luminescente ad ampia area (30x30 cm2) con una efficienza di potenza ottica record del 6.8%. In seguito, discuto gli effetti del drogaggio ad impurezza elettronica in NC di calcogenuri binari sintetizzati tramite una innovativa procedura di crescita “a seme” che risulta in un numero preciso di droganti in ogni NC, quindi superando il limite poissoniano per le loro proprietà di semiconduttori magnetici diluiti (DMS). Studi strutturali, spettroscopici e magneto-ottici descrivono in dettaglio i processi fisici coinvolti, dovuti al livello di drogaggio esatto dei NC. Gli atomi d’oro, inseriti come droganti per la prima volta all’interno di NC II-VI, sono incorporati come specie non magnetica Au+ ed attivano una PL intensa e variabile con la dimensione all’interno del gap del semiconduttore, modificando artificialmente l’occupazione della banda di valenza. Fondamentalmente, la conversione transiente degli Au+ in Au2+ paramagnetici (configurazione 5d9) sotto eccitazione ottica genera sia un forte magnetismo che un comportamento da DMS che dimostrano il contributo delle singole impurezze paramagnetiche al magnetismo macroscopico dei NC, sbloccando il loro potenziale applicativo in dispositivi quantici e di spintronica. Inoltre, riporto gli effetti del drogaggio sostituzionale con atomi paramagnetici in NC di perovskite CsPbCl3 drogati con Mn2+ e rivelo il meccanismo di trasferimento di energia specifico che coinvolge stati di difetto poco profondi che risultano nella duplice emissione di PL e inducono uno Stokes shift vantaggioso per tecnologie di gestione fotonica. Infine, concludo mostrando gli effetti della anisotropia di forma in sistemi di NC colloidali con la sintesi e lo studio di nanoplateles bidimensionali di CdTe. Inoltre, mostro alcuni dati spettroscopici preliminari che rendono questi sistemi molto attraenti per applicazioni nella tecnologia laser e di rilevamento di radiazione ultraveloce. Nel corso di questo lavoro, ho lavorato sulla sintesi colloidale delle nanostrutture e studiato i sistemi nanocristallini menzionati usando tecniche di caratterizzazione strutturale come la diffrazione di raggi X e la microscopia a trasmissione elettronica. Tecniche spettroscopiche tra cui l’assorbimento transiente ultraveloce, la PL a stato stazionario e risolta in tempo a temperature criogeniche, il dicroismo circolare magnetico e la risonanza paramagnetica di elettroni sono state usate per investigare queste nanostrutture, chiarendo la loro fotofisica fondamentale e sfruttando i loro potenziali applicativi in tecnologie moderne e di nuova generazione.
Colloidal semiconductor nanocrystals (NCs), owing to their size-tuneable electronic properties and solution processability, have long been proposed as versatile chemically synthesized alternatives for many photonic, optoelectronic, and quantum computational technologies as well as super-atomic functional building blocks for bottom-up assembled artificial metamaterials. Since their original discovery over 30 years ago, tremendous advancements in colloidal and surface chemistry, NC physics, and device application have brought this vision closer to reality. In this work I explore these photophysical phenomena in four different NC systems diversified by chemical composition and shapes. I studied the most favorable intrinsic ternary CuInS2 NCs which inherently offers heavy metal free, non-toxic alternatives to the existing Cd and Pb based materials with a large Stokes shift and long photoluminescence decay time. The origin of these optical properties in CuInS2 NCs were however not fully understood with conflicting theories describing its characteristic aforementioned properties. Here, subsequential to experimentally confirming the valence band fine structure origin of luminescence in these nanostructures, we utilized the optimized NCs and fabricated a large area Luminescent solar concentrator of 30ˣ30 cm2 area with record Optical Power Efficiency of 6.8% to the date. Then, I discuss the effects of electronic impurity doping in binary chalcogenide NCs synthesized by a novel seeded growth procedure resulting in quantized dopants in each NC thus overcoming the Poissionian bottleneck for their diluted magnetic semiconductor properties. Structural, spectroscopic, and magneto-optical investigations trace a comprehensive picture of the physical processes involved, resulting from the exact doping level of the NCs. Gold atoms, doped here for the first time through the reaction protocol into II−VI NCs, are found to incorporate as non-magnetic Au+ species activating intense size-tuneable intragap photoluminescence and artificially offsetting the hole occupancy of valence band states. Fundamentally, the transient conversion of Au+ to paramagnetic Au2+ (5d9 configuration) under optical excitation results in strong photoinduced magnetism and diluted magnetic semiconductor behaviour revealing the contribution of individual paramagnetic impurities to the macroscopic magnetism of the NCs unlocking their potential to be exploited for applications in quantum and spintronic devices. Moreover, I communicate the effects of substitutional doping with paramagnetic atoms in Manganese doped CsPbCl3 perovskite NCs and reveal a peculiar energy transfer mechanism involving shallow defects states subsequently resulting in dual emission and inducing Stokes shift desirable for photon management technologies. Finally, I conclude by talking about the effect of shape anisotropy in colloidal NC systems by synthesizing and studying two-dimensional colloidal CdTe nanoplatelets. Moreover, I report some very interesting preliminary spectroscopic data that presents these NC systems at great heed with respect to their application in lasing technology and in Ultrafast radiation detection applications. Through the course of my PhD, I worked on the colloidal synthesis of nanostructures, and studied the aforementioned NC systems using structural characterization techniques like X-Ray diffractions and transmission electron microscopy. Spectroscopic techniques including ultrafast transient absorption, steady state and time resolved photoluminescence spectroscopy at cryogenic temperatures, magnetic circular dichroism and electron paramagnetic resonance were used to study and report these nanostructures, thus elucidating their fundamental photophysics and exploit their applicative potential in modern, next generation technologies.

Le compose babio#3, connu pour ses proprietes supraconductrices lorsqu'on substitue le bismuth par le plomb, a suscite un regain d'interet lorsqu'une temperature supraconductrice de 30 k environ a ete obtenue en le dopant avec du potassium. Nous avons caracterise finement par analyse e. D. X. Des monocristaux prepares soit par flux soit par electrocristallisation. Nous avons montre que dans les deux cas seuls les cristaux faiblement dopes (moins de 10% de potassium) etaient homogenes. Au-dela de ce taux de substitution, ils presentent soit un gradient de composition, soit plusieurs compositions distinctes. Ceci se traduit en general par un elargissement de la transition supraconductrice mesuree en susceptibilite alternative. Nous avons aussi mis en evidence deux nouvelles phases, l'une contenant du sodium, l'autre presentant un rapport (ba+k)/bi different de celui relatif a une phase perovskite. Par ailleurs, nous avons determine par diffraction des rayons x la structure d'un monocristal macle de composition k#0#. #0#2#3ba#0#. #9#9#4bi#0#. #9#7#4o#2#. #9#5. Les meilleurs affinements ont ete obtenus en decrivant la structure dans le groupe d'espace i2/m, comme pour le compose non dope. Nous avons trouve que pour cette faible concentration en potassium les atomes de potassium ne substituaient pas le baryum mais etaient situes sur l'un des deux sites de bismuth. Le meme type d'etude faite sur un monocristal de babio#3 dope au plomb (13%) a montre que la encore c'etait le groupe d'espace i2/m qui permettait la meilleure description de la structure. Enfin, nous avons determine la structure d'une nouvelle phase de type perovskite double, de formule ba#3#. #1#2k#0#. #6#8bi#3#. #4#4na#0#. #7#0o#1#2. La repartition des charges laisse peu d'espoir de rendre ce compose supraconducteur

Etude de la cinetique et des mecanismes d'oxydation thermique de films dopes a 210**(20) cm**(-3) b "in situ" et par implantation post-depot. Les resultats prennent en compte les influences du mode de dopage et de la microstructure initiale des films (qui varie d'un etat quasi-amorphe a un etat nettement polycristallin). Leur analyse s'appuie sur a) un logiciel de modelisation de l'oxydation de si et la comparaison avec la cinetique d'oxydation de temoins monocristallins qui permettent de les exprimer en termes de constante de diffusion d et de la vitesse de reaction de surface k::(s) de l'oxydation, b) la comparaison entre depots non dopes, dopes a b par implantation ou "in situ" et c) le suivi des proprietes structurales (rugosite, diagrammes rheed, observations tem) et electroniques des films

L'essor actuel des technologies soi est lie a la production d'un materiau de depart de qualite, dont le juge final est le comportement electrique des circuits integres. Cette these decrit des ameliorations et de nouvelles idees pour l'evaluation des proprietes electriques des materiaux soi. Les methodes presentees sont appliquees en priorite au nouveau materiau unibond. Nous donnons d'abord une vue d'ensemble des technologies soi et des methodes de caracterisation disponibles. Nous exposons ensuite notre contribution en commencant par la mesure electrique d'epaisseur du film de silicium dans un dispositif mos, pour laquelle nous proposons une extension d'une methode existante. La duree de vie des porteurs dans le film de silicium est ensuite etudiee par les techniques recentes des transitoires de courant de drain dans des transistors mos. Nous montrons la necessite d'une approche statistique pour comparer entre eux divers materiaux soi. Nous presentons ensuite des methodes de caracterisation rapide, ne necessitant pas la fabrication de dispositifs. L'oxyde enterre et le substrat silicium sous-jacent sont etudies par sonde a mercure, apres elimination du film de silicium par voie chimique. Pour la mesure du dopage residuel du film mince soi, nous evaluons les possibilites du pseudo-transistor mos. Nous proposons par ailleurs une nouvelle methode pour determiner tres rapidement et sans ambiguite le type, applicable aux tres faibles dopages. La derniere partie est consacree a l'oxyde de grille des technologies mos-soi. Une etude en time dependent dielectric breakdown sur dispositifs mos nous permet de montrer que le comportement en claquage intrinseque est identique sur soi et sur silicium massif. Pour s'affranchir du cout et de la longueur d'une telle etude, nous proposons une nouvelle methode simple de caracterisation d'oxyde de grille sur soi, ne necessitant pas d'autre etape technologique que la realisation de l'oxyde lui-meme.

EDELWEISS est une expérience de détection directe de matière noire froide non-baryonique sous forme de particules massives et faiblement interagissantes (connues sous l'acronyme de WIMPs), qui constituent actuellement les candidats les plus populaires pour rendre compte de la masse manquante de l'Univers. Dans ce but, EDELWEISS utilise des bolomètres de germanium opérés à température cryogénique (20 mK environ) dans le Laboratoire Souterrain de Modane (LSM) à la frontière franco-italienne. En particulier, depuis 2008, un nouveau type de détecteur est en fonctionnement, équipé d'électrodes concentriques pour optimiser le rejet des évènements de surface (détecteurs à grilles coplanaires). Cette thèse se décompose en plusieurs axes de recherche. Tout d'abord, nous avons réalisé des mesures concernant la collecte des charges dans les cristaux. Les lois de vitesse des porteurs (électrons et trous) ont été déterminées dans le germanium à 20 mK dans la direction <100>, et une étude complète de la répartition des charges a été menée, avec une évaluation de l'anisotropie du transport et de la diffusion transverse des porteurs. Ces résultats permettent d'avoir une meilleure compréhension du fonctionnement interne des détecteurs d'Edelweiss. Ensuite, des études portant sur l'amélioration des performances ont été effectuées. Nous avons en particulier permis d'optimiser la procédure de régénération des cristaux et améliorer le rejet passif des évènements de surface (β). Le volume utile de détection des détecteurs a été évalué en utilisant les raies de deux radio-isotopes activés cosmiquement, le 68Ge et le 65Zn. Enfin, une étude exhaustive portant sur l'étude des spectres à basse énergie a été menée, ce qui permet de mettre au point une méthode d'analyse systématique pour la recherche de WIMPs de basse masse dans EDELWEISS
EDELWEISS is a direct non-baryonic cold dark matter detection experiment in the form of weakly interacting massive particles (also known as WIMPs), which currently constitute the most popular candidates to account for the missing mass in the Universe. To this purpose, EDELWEISS uses germanium bolometers at cryogenic temperature (20 mK approximately) in the Underground Laboratory of Modane (LSM) at the French-Italian border. Since 2008, a new type of detector is operated, equipped with concentric electrodes to optimize the rejection of surface events (coplanar-grid detectors). This thesis work is divided into several research orientations. First, we carried out measurements concerning charge collection in the crystals. The velocity laws of the carriers (electrons and holes) have been determined in germanium at 20 mK in the <100> orientation, and a complete study of charge sharing has been done, including an evaluation of the transport anisotropy and of the straggling of the carriers. These results lead to a better understanding of the inner properties of the EDELWEISS detectors. Then, studies relating to the improvement of the performances were carried out. In particular, we have optimized the space-charge cancellation procedure in the crystals and improved the passive rejection of surface events (β). The fiducial volume of the detectors has been evaluated using two X-ray lines from cosmically activated radionuclides: 68Ge and 65Zn. Lastly, an exhaustive study of the low energy spectra has been carried out, which makes it possible to develop a systematic analysis method for the search of low-mass WIMPs in EDELWEISS

Le sujet de cette thèse concerne la modélisation et la simulation numérique de la diffusion des dopants dans les composants microoptoélectroniques à base de matériaux III-V. Cette diffusion peut se produire au cours des traitements thermiques nécessaires à la fabrication des composants (épitaxie, réalisations de contacts,. . . ) Dans un premier temps, les aspects physiques et technologiques de la diffusion sont abordés. Une attention particulière est accordée au mécanisme substitutionnel-interstitiel de diffusion. La modélisation de la diffusion des dopants de type p dans les matériaux III-V aboutit à la résolution numérique de systèmes non linéaires d'équations différentielles aux dérivées partielles. Deux méthodes ont été utilisées : la méthode des différences finies sur le temps et sur l'espace et la méthode des lignes. Plusieurs phénomènes physiques sont pris en compte dont les mécanismes de Frank/Turnbull et du kick-out auxquels s'ajoutent les effets des charges électriques, du champ électrique et de l'effet du niveau de Fermi. Dans une dernière partie sont présentées les simulations des profils de diffusion du béryllium dans l'InGaAs. L'ensemble des résultats obtenus est discuté et comparé avec les données précédemment publiées.

博士
國立彰化師範大學
光電科技研究所
104
This study investigates the effect of Co, Mn, and Cu content on the structural, luminescence, and magnetic properties of sol-gel ZnCoS, ZnMnS, and ZnCuS films by x-ray diffraction (XRD), photoluminescence (PL), energy dispersive spectrometer (EDS), atomic force microscopy (AFM), and alternating gradient magnetometer (AGM) measurements. Dependences of optical properties and crystal structure upon Co, Mn, and Cu content were found. In addition, combining with PL, XRD and AGM results, a direct link between the magnetization and defects of sol-gel ZnCoS, ZnMnS, and ZnCuS films was established. Currents through Cu-doped ZnS (ZnCuS)/n-type Si structures were studied. The electrical conduction investigations suggest that the carrier transport behavior is governed by the Poole–Frenkel emission for ZnCuS/n-type Si devices having the low Cu concentration. However, the carrier transport behavior is governed by the thermionic emission for ZnCuS/n-type Si devices having the high Cu concentration. The photoluminescence result revealed that sulfur vacancy (VS) is the origin of conduction behavior conversion. The dependence of VS on the film composition was identified for providing a guide to control the current transport behavior of ZnCuS/n-type Si devices.

碩士
義守大學
材料科學與工程學系
101
In this study, we prepared TiO2 optical thin film by RF-sputtering method at room temperature and doped with different contents of glass dopants (1wt%, 3wt%, 5wt%, 10wt%, 15wt%, 20wt%). Ar was used as a sputtering gases. TiO2 optical thin films were deposited on glass substrate and the silicon substrate and annealed (550℃, 650℃, 750℃, 850℃) at 90%N2 with 10%H2 atmosphere to discuss the effects of different doping and annealing conduction on the properties of TiO2 films. The results shows that increasing glass dopants are affected crystal structure. The crystal of TiO2 films are changed from anatase phase to amorphous phase as glass dopants were increased. The FE-SEM images showed that annealing temperature affected grain size of the films. Transmittance and refractive index of the films has the opposite results. The 1wt% doping TiO2 thin film has the best transmittance around 85-95% and the 20wt% doping TiO2 thin film has the best refractive index around 2.37-2.41. The densification of TiO2 films can calculated based on the refractive index of the films. The results showed that the TiO2 film with 20wt% doping has the densest structure with porosity around 10.3-13.5%.

碩士
國立彰化師範大學
物理學系
99
The effects of surface treatment or impurity doping on the optical property and crystal structure of ZnO nanoparticles, made by sol-gel method, was investigated in this study. We get the properties of ZnO nanoparticles according to observed the result from X-ray diffraction, scanning electron microscope, photoluminescence, Fourier-transform infrared spectroscopy, Raman spectroscopy, and contact angle measurements. It is found that ZnO nanoparticles released from compressive stress after surface modification, and the crystalline size became smaller. In addition, surface modification led to the formation of surface oxygen vacancies and the production of hydroxyl adsorption, that induced ZnO hydrophilic. Li doping led to the increase of the oxygen-vacancy-related defects density in ZnO nanoparticles. In addition, the photoluminescence intensity of Li-doped ZnO is stronger than un-doped ZnO because the decrease in the probability of nonradiative recombination. The intensity of the Ti-doped ZnO diffraction peaks remarkably decreases with increasing Ti content, suggesting the weakened crystallinity. Ti doping also led to the reduced oxygen-vacancy-related defects in ZnO nanoparticles.

M.Sc.
Impurity resonance scattering effects are investigated in the Cr-Ga alloy system. This system has a triple point on its magnetic phase diagram where the paramagnetic (P), incommensurate (I) and commensurate (C) spin-density-wave (SDW) states co-exist. Alloying Cr with the nonmagnetic nontransitional element Ga affects the magnetic properties of Cr in a very unique way. In order to investigate the presence of resonant impurity scattering effects in binary Cr-Ga alloys, electrical resistivity measurements were carried out in the temperature range between 6 K and 85 K. The results of the investigation show: • A nonmonotonic increase in the residual resistivity of the Cr-Ga system with an increase in the Ga content, due to the presence of resonant impurity scattering of conduction electrons. • A low-temperature resistivity minimum observed in some of the Cr-Ga alloys, taken as further evidence for the presence of resonant impurity scattering effects on the conduction electrons. The impurity resonance scattering effects on the electrical resistivity of a Cr + 1.2 at.% Ga alloy, doped with V and Mn to tune the Fermi level through the impurity level, are also investigated. The investigation was complemented by thermal expansion and velocity of sound measurements in the temperature range 77 K to 450 K for the Cr + 1.2 at.% Ga alloy only. This specific Ga concentration was chosen to allow for studying resonant scattering effects in both the ISDW and CSDW phases of the system. This is possible because concentration of 1.2 at.% Ga is just above the triple point concentration. Doping with Mn to increase the electron concentration (eA) drives the alloy deeper into the CSDW phase region of the phase diagram, while doping with V, on the other hand, will drive the alloy towards the ISDW phase region. The results of the study are summarized as follows: • Two relatively sharp peaks, attributed to resonant impurity scattering effects, are observed in the curve of the residual resisitivity as a function of dopant concentration in the ISDW phase of the ternary (Cr0.988Ga0.012)1-xVx and (Cr0.988Ga0.012)1-yMny alloy systems. v • At 0 K the (Cr0.988Ga0.012)1-yMny alloy system transforms from the ISDW to the CSDW phase at y ≅ 0.0032, giving a CSDW phase for y > 0.0032. A peak is observed in the residual resistivity at about this Mn content. This peak can then either be ascribed to a jump occurring in the residual resistivity when the CSDW phase is entered from the ISDW phase or to resonant scattering effects. The conclusion is that the peak is rather related to the latter effect. • The resistivity as a function of temperature of the above two ternary alloy series show well-developed or weak minima at low temperatures for some of the samples. This is taken as further evidence of the influence of impurity resonant scattering effects on the resistivity of these alloys. • The resistivity and thermal expansion coefficient of the polycrystalline Cr0.988Ga0.012 alloy of the present study behaves anomalously close to the ISDW-CSDW phase transition temperature and warrant further investigation. The concentration-temperature magnetic phase diagram of the (Cr0.988Ga0.012)(Mn,V) alloy system was constructed from the magnetic transition temperatures obtained from electrical resistivity measurements. Theoretical analysis of the phase diagram was done using the two-band imperfect nesting model of Machida and Fujita. The results show: • A triple point at (0.21 at.% V, 225 K) where the ISDW, CSDW and P phases coexist on the magnetic phase diagram. • The curvature of all three theoretically calculated phase transition lines in the region of the triple point is of the same sign as that observed experimentally. • The theoretical fit is very good for the ISDW-P and ISDW-CSDW phase transition boundaries, while there is some discrepancy for the CSDW-P phase transition line. This may be attributed to the fact that the theory is one dimensional and that it does not include electron-hole pair breaking effects due to impurity scattering and also not effects of changes in the density of states due to alloying.
Dr. A.R.E Prinsloo Prof. H.L. Alberts

博士
國立交通大學
應用化學系
89
The effect of impurity doping, photoluminescent, afterglow, and thermoluminescent properties and for long phosphorescent SrAl2O4:Eu2+, Dy3+ (SAED) and some analogous phosphors derived from a sol-gel synthetic route have been investigated. The improvement on phosphorescence intensity and the lengthening of afterglow persistent time has been observed in the SAED phases with the addition of boron or silicon. In order to investigate the photoluminescence, afterglow, defects and the depth energy of the traps, we have measured the X-ray diffraction (XRD) profiles, SEM and DTA/TGA, photoluminescence (PL), afterglow (AG) and thermoluminescence (TL) spectra to characterize the microstructure and luminescent properties that are relevant to the nature of defects present in long afterglow SAED phases. The SAED phases derived from sol-gel route exhibit smaller grain size and poorer crystallinity, as compared to those synthesized by solid-state method. The wavelength of afterglow (lAG) for SAED derived from sol-gel processes was found to be shorter than lAG for those prepared via solid-state route, which was attributed to difference in host crystal field strength for Eu2+. The effect of host compositions on the PL and AG spectra of SAED phases has also been investigated for samples prepared from starting host precursors with different Al/Sr compositions. We found that Sr3Al2O6 dominated in strontium aluminate with the host precursors with Al/Sr < 1; SrAl2O4 was observed in those with 2 < Al/Sr < 3; however, more than 95% of SrAl12O19 was discovered in those with 9 < Al/Sr ≦12. The amount of SrAl2O4 present in the host with various Al/Sr ratios was found to be critical in the determining the afterglow intensity and the afterglow persistent time, as indicated by the AG curves for SAED phases. The coexistence of SrAl12O19 in the SAED host was found to affect the afterglow duration, whereas that of the Sr3Al2O6 phase was found to be independent of the afterglow persistence. The effect of boron and silicon doping in the SAED phosphors was found to not only increase the crystal defects but also enhance the afterglow intensity. The boron-doped SAED (BSAED) sample was observed to exhibit stronger phosphorescence intensity and longer afterglow duration. This observation can be attributed to the non-homogeneous distribution of glassy strontium borates that promotes the reduction of Eu2+ and increases the trap depth energy, as indicated by surface microstructure analysis of BSAED. The twin peaks observed in the afterglow curves for BSAED phases could probably be attributed to two different traps with different depth energies, as compared to one singlet emission observed in the PL spectra. The hole trapping effect due to Dy3+ codoping in SrAl2O4:Eu2+,Dy3+ phase can be effective only when the samples were reduced under a reducing H2/N2 atmosphere at 1,300℃, as indicated by the TL curve analysis. Otherwise, shallow traps will form as that found in SrAl2O4:Eu2+. In addition, the codoping of Nd3+ coactivator in the SrAl2O4:Eu2+,Nd3+ phase indicated that the Nd3+-doping only increases the afterglow intensity, but doesn’t increase the trap depth, which is similar to the shallow traps present in the SrAl2O4:Eu2+ phase. Based on the experimental Hoogenstraaten’s plots, the calculated trap depth energy was found to be 0.57—0.76 eV, 0.43 eV, and 0.18 eV for SrAl2O4:Eu2+0.05,Dy3+0.05,B0.3, SrAl2O4: Eu2+0.05, Dy3+0.05, and SrAl2O4:Eu2+0.05, respectively, as compared to 0.59 — 0.72 eV for BG-300M.manufactured by Nemoto Co. These results indicate the similarity of nature of the trap levels for all strontium aluminate phosphors described in this research.

The present project has made a comprehensive assessment of the effect of Nb doping on various charge-transfer related properties of TiO2. Of particular focus, the electrical properties of Nb-doped TiO2 (0.65 at %) have been investigated using the simultaneous measurement of electrical conductivity and thermoelectric power. This investigation was undertaken at elevated temperatures (1073 K -- 1298 K) in equilibrium with a gas phase of controlled oxygen activity (10-10 Pa < p(O2) < 75 kPa). In addition, the effect of segregation on the surface versus bulk composition of Nb-doped TiO2 was also investigated at a function of temperature and oxygen activity. Specifically, the following determinations were undertaken: The effect of oxygen activity, p(O2) and temperature on both electrical conductivity and thermoelectric power The effect of Nb on the defect disorder and related electrical properties of TiO2 The determination of equilibration kinetics and the associated chemical diffusion data for Nb-doped TiO2 The determination of Nb bulk diffusion in TiO2 The effect of p(O2), temperature and dopant content on Nb segregation and the related surface composition of Nb-doped TiO2 The obtained electrical properties enable the determination of a defect disorder model for Nb-doped TiO2, which may be considered within the following p(O2) regimes: Strongly Reduced Regime. In this regime, the predominant ionic defect was anticipated to be oxygen vacancies compensated electronically by electrons. While the transition to this regime (from higher p(O2)) was clearly observed, the predominant defect disorder existing beyond this transition was not confirmed due to an inability to obtain sufficiently low oxygen activity. Metallic-type conductivity behaviour was observed within this transition region. Reduced Regime I. In this regime, the predominate defect disorder defined by the electronic compensation of incorporated Nb ions by electrons was clearly observed. Reduced Regime II. In this regime, the predominate defect disorder defined by the ionic compensation of incorporated Nb ions by quadruply-charged titanium vacancies, was clearly observed. The present project included the determination of diffusion data which included: Temperature dependence of 93Nb tracer diffusion in single crystal TiO2 over the temperature range 1073 K -- 1573 K Chemical diffusion coefficient over the temperature range 1073 K -- 1298 K and oxygen activity range, 10-10 Pa < p(O2) < 75 kPa These pioneering studies are significant as they enable the prediction of the processing conditions required to reliably 1) incorporate Nb into the TiO2 lattice, and 2) achieve equilibrium with the gas phase. Finally, the present project included investigations on the effect of Nb segregation on the surface composition of Nb-doped TiO2, with the following outcomes: Due to segregation, the surface can be significantly enriched in Nb compared to the bulk The extent of enrichment increases as the bulk Nb content or the oxygen activity is decreased Following enrichment, the surface Nb concentration could be sufficiently high to assume a unique surface phase The outcomes of the present project are significant as they can enable the processing of TiO2 with enhanced charge transport and controlled surface properties.