Minority carrier transport properties and the effects of electron irradiation/injection were studied in GaN and ZnO containing dopants known to form acceptor states deep within the materials' bandgap. Minority carrier diffusion length and lifetime changes were investigated using Electron Beam Induced Current (EBIC) method, cathodoluminescence spectroscopy, spectral photoresponse and persistent photoconductivity measurements. It is shown that electron irradiation by the beam of a scanning electron microscope results in a significant increase of minority carrier diffusion length. These findings are supported by the cathodoluminescence measurements that demonstrate the decay of near-band-edge intensity as a consequence of increasing carrier lifetime under continuous irradiation by the electron beam. Temperature-dependent measurements were used to determine the activation energies for the electron irradiation-induced effects. The latter energies were found to be consistent with the involvement of deep acceptor states. Based on these findings, the effects of electron irradiation are explained via the mechanism involving carrier trapping on these levels. Solid-state electron injection was also shown to result in a similar increase of minority carrier lifetime and diffusion length. Solid-state injection was carried out by applying the forward bias to a ZnO homojunction and resulted in a significant improvement of the peak photoresponse of the junction. This improvement was unambiguously correlated with the increase of the minority carrier diffusion length due to electron injection.

No description available.

No description available.

This dissertation examines the carrier transport properties, diffusion length, effective carrier lifetime, and resistivity in two wide bandgap materials, GaN and diamond. A combination of two methods was used to obtain these transport properties. The two were optical beam induced current (OBIC) and electron beam induced current (EBIC) time of flight transient measurements. These techniques consist of measuring the current response to the drift and diffusion of generated electron-hole pair carriers created by a short-duration pulse of radiation. Under OBIC, a short duration pulsed optical source, with an electron beam excitation pulse time much less than the transit time of the material, was used to generate excess carriers within the absorption depth of the material. The second method of excitation, EBIC involved the use of a modified SEM with a photoemission source (L-EBIC) and a high speed pulsed thermionic electron source (T-EBIC) to generate an electron beam. This electron beam was used to create a large number of electron-hole pairs at various penetration depths within the materials. Measurements on GaN found the diffusion length was 7.84 µm with the L-EBIC and 7.78 µm with the T-EBIC. After annealing at 900°C for 30 min. the GaN diffusion length increased to 9.89 µm (L-EBIC). The dark resistivity was 1.79 x 10¹⁰Ω-cm, and the carrier lifetimes were 1.7 µs with L-EBIC and 3.36 & 3.9 ns with OBIC. The author believed that the L-EBIC result was a good representation of the carrier lifetime within the material, while the shorter OBIC results were due to the combine high surface and interface recombination processes. The diamond dark resistivity was found to be 6.14 x 10¹¹Ω-cm and the diffusion lengths were 94.1 µm and 97 µm from the L-EBIC and T-EBIC respectively. All measurements were within 10 % spread. The real value of this contribution lies in determining the diffusion lengths in GaN and diamond by the EBIC techniques, measuring the effective surface\interface and thin film carrier lifetime of GaN utilizing a combination of OBIC and L-EBIC techniques, and evaluating the dark resistivity in GaN and diamond materials. These measurements can lead to a better understanding and exploitation of the electrophysical behavior of these materials. / Ph. D.

Apresentamos neste trabalho uma técnica nova e simples para medida de propriedades de transporte e de cinética de portadores em semicondutores isolantes fotocondutivos. Determinamos propriedades importantes como comprimento de difusão e produto mobilidade-tempo de vida dos portadores no silício amorfo hidrogenado (a-SI:h). Esta técnica baseia-se no efeito de uma grade de concentração de fotoportadores em estado estacionário, criado pela luz de um laser, na condutância de um semicondutor. Assim é possível determinar indiretamente as propriedades de transporte ou de cinética pela simples medida da fotocondutividade na presença de grade de fotoportadores em diferentes condições. o a-S-:h é um semicondutor relativamente novo que merece destaque devido a sua potencialidade para aplicação. Ele é um excelente material fotocondutor produzido na forma de filmes finos. É atualmente largamente utilizado em células solares, fotosensores de grande área e transistores de filmes finos. A sua obtenção, apesar de ser simples, envolve processos complexos e empíricos no processo de formação dos filmes. Portanto é vital o conhecimento das propriedades de transporte e cinética deste material como uma referência da qualidade do material produzido. / In this work we present a new and simple technique to measure transport and kinetic properties in photoconductive insulator semiconductors. Important properties as diffusion length and mobility-lifetime product of hydrogenated amorphous silicon (a-SI:h) was determined. This technique is based on the effect of a steady-state photocarrier grating concentration in the semiconductor conductance created by laser light. It is possible to determine indirectly the transport and kinetic properties simply by measuring photoconductive in the presence of photocarrier grating under diferents condition. The a-SI:h is a reactive new semiconductor with an outstanding potenciality for applications. It is an excellent photoconductor material produced in thin-film forms. Nowadays it has been used in large scale in solar cells, big area photosensor and thin-¬film transistor. Although its production is simple, the formation process of the thin-films is complex and empirical. Therefore the value of the transport and kinetic properties of this material is essential as a reference of quality of the produced material.

La durée de vie des porteurs minoritaires est l'un des principaux paramètres mesurés dans les semi-conducteurs et la décroissance de photoconductivité (PCD) l'une des méthodes les plus largement utilisées pour ce type de mesure. Aujourd'hui, grâce aux divers équipements automatisés, la mesure de durée de vie est devenue une caractérisation de routine qui permet de juger de la qualité d'un matériau dans tous les secteurs utilisant les semi-conducteurs. Cependant, l'utilisation de micro- et nano-matériaux dans l'industrie du photovoltaïque et de la microélectronique requière l'adaptation des techniques existantes (PCD, photoluminescence etc.). En effet, avec la réduction des dimensions (couches ultraminces telles que les couches épitaxiées, couches SOI « silicon on insulator », et nanostructures), l'influence de la surface (états d'interfaces, pièges, etc.) devient prépondérante. La présence des substrats utilisés pour les croissances ou report de couche de ces différentes structures perturbe également les mesures. Ceci rend difficile l'adaptation des méthodes de mesure de durée de vie classiques comme, par exemple, le déclin de photoconductivité. Au cours de cette thèse nous nous sommes attachés à adapter des techniques de caractérisation de durée de vie à des matériaux de faibles dimensions. Nous avons tout d'abord caractérisé des échantillons massifs et des couches épitaxiées d'une épaisseur de l'ordre de la dizaine de micromètres. Nous avons proposé une technique qui consiste à déterminer simultanément la durée de vie en volume et la vitesse de recombinaison en surface des porteurs minoritaires dans d'une couche épitaxiée, à partir de la mesure de l'intensité de photoluminescence. La méthode développée consiste à calculer le rapport de l'intensité de photoluminescence (RPL) mesurée à différentes longueurs d'onde et pour différentes puissances d'excitation. Ces rapports RPL expérimentaux sont ensuite comparés aux rapports RPL simulés, ce qui permet d'évaluer la vitesse de recombinaison en surface et le temps de vie en volume. Nous avons ensuite étudié des couches semi-conductrices ultraminces de l'ordre de la centaine de nanomètres dans des structures de type SOI (silicon on insulator). Après un rappel des méthodes de fabrication et de quelques-unes des utilisations, nous avons analysé les méthodes électriques existantes permettant de déterminer la qualité des substrats SOI. Cela nous a amené à proposer une nouvelle méthode de caractérisation apportant des solutions aux limitations de ces techniques. Cette méthode se base sur une mesure courant-tension sous obscurité et sous éclairement en configuration PSEUDO-MOSFET où le substrat de la structure SOI sert de grille du transistor et deux pointes déposées sur le film de silicium servent de source et drain. Nous avons appliqué cette nouvelle méthode de caractérisation de la durée de vie des porteurs de charge à un substrat SOI et avec l'aide de la simulation numérique, nous avons pu expliquer les phénomènes de recombinaison aux interfaces et extraire les paramètres associés. Enfin, la dernière partie de ce travail de thèse concerne l'étude des nanofils pour des applications photovoltaïques. Dans les nanofils, le rapport surface sur volume augmente considérablement ce qui entraîne une diminution de la durée de vie effective due à l'augmentation de l'influence des surfaces. Le fonctionnement des cellules solaires à base de nanofils que nous avons étudiées est très dépendant de la qualité des interfaces. Nous avons analysé ces cellules grâce à la méthode RRT (« Reverse Recovery Transient ») basée sur la proportionnalité qui existe entre la quantité de charges stockées dans les régions neutres des jonctions pn polarisées et la durée de vie des porteurs minoritaires. Ce type de structure étant assez complexe, nous avons utilisé des simulations numériques pour analyser les phénomènes de recombinaison au sein de la cellule solaire et extraire les densités de défauts aux interfaces. / The minority carrier lifetime is one of the main parameters used to analyse the semiconductors quality and photoconductivity decay (PCD) is one of the most widely used lifetime characterization method. Thanks to the variety of automated equipment that has developed, lifetime measurement has become a routine technique to assess the quality of semiconductors. However, the micro and nano materials used in the photovoltaic and microelectronics industry require an adaptation of the existing methods (PCD, photoluminescence etc.). Indeed, with reduced dimensions (epitaxial layers, SOI “Silicon on Insulator”, nanostructures and nanowires), the influence of the surface (interface states density, traps, etc.) becomes predominant. The presence of the substrates used for the material growth or for the layer transfer can also influence the measures. Consequently traditional methods of lifetime measurement are difficult to apply to low dimensional materials. This thesis is focused on the measurement of minority carrier lifetime in micro and nano materials (bulk, epitaxial layer, silicon on insulator and nanowires) with a special emphasis on the adaptation of the characterization tools to the material thickness. We have studied first bulk samples and epitaxial layers (with thicknesses around 50µm) by photoluminescence. We have developed a method to determine simultaneously the bulk lifetime and the surface recombination velocity using room temperature photoluminescence measurement. The procedure consists in measuring the photoluminescence intensity ratio at different incident laser wavelengths and power. These photoluminescence ratios are then compared with analytical simulations, which allow us to evaluate the surface recombination velocity and the bulk lifetime. We have then investigated SOI (Silicon on insulator) structures with ultrathin semiconductor layers of the order of 100 nanometers. After a brief description of the manufacturing methods and of some of their uses, we have analyzed the existing electrical methods used to evaluate the quality of SOI substrates. This led us to propose a new characterization method to overcome the limitations of these techniques. This method is based on a current-voltage measurement in the dark and under illumination called PSEUDO-MOSFET (the substrate of the SOI structure serves as the transistor gate and the two contact points deposited on the silicon film are used as the source and drain). We applied this new method to characterize the lifetime of a SOI substrate and with the help of numerical simulation, we were able to explain the recombination mechanism associated with interfaces and extract the parameters. Finally, the last chapter concerns the study of nanowires for photovoltaic applications. In the nanowires, the surface to volume ratio greatly increases leading to a decrease of the effective lifetime due to the increased influence of the surfaces. In this chapter, we have studied the minority carrier lifetime in core-shell nanowire-based solar cells under dark conditions with a purely electrical approach called reverse recovery transient (RRT). This method is based on storage time measurement which depends essentially on the amount of stored charges in the biased junction and can be used to calculate the minority carrier lifetime. Numerical simulations have also been done to explain the measurements and to validate the theory and the hypotheses used for parameter extraction.

Apresentamos neste trabalho uma técnica nova e simples para medida de propriedades de transporte e de cinética de portadores em semicondutores isolantes fotocondutivos. Determinamos propriedades importantes como comprimento de difusão e produto mobilidade-tempo de vida dos portadores no silício amorfo hidrogenado (a-SI:h). Esta técnica baseia-se no efeito de uma grade de concentração de fotoportadores em estado estacionário, criado pela luz de um laser, na condutância de um semicondutor. Assim é possível determinar indiretamente as propriedades de transporte ou de cinética pela simples medida da fotocondutividade na presença de grade de fotoportadores em diferentes condições. o a-S-:h é um semicondutor relativamente novo que merece destaque devido a sua potencialidade para aplicação. Ele é um excelente material fotocondutor produzido na forma de filmes finos. É atualmente largamente utilizado em células solares, fotosensores de grande área e transistores de filmes finos. A sua obtenção, apesar de ser simples, envolve processos complexos e empíricos no processo de formação dos filmes. Portanto é vital o conhecimento das propriedades de transporte e cinética deste material como uma referência da qualidade do material produzido. / In this work we present a new and simple technique to measure transport and kinetic properties in photoconductive insulator semiconductors. Important properties as diffusion length and mobility-lifetime product of hydrogenated amorphous silicon (a-SI:h) was determined. This technique is based on the effect of a steady-state photocarrier grating concentration in the semiconductor conductance created by laser light. It is possible to determine indirectly the transport and kinetic properties simply by measuring photoconductive in the presence of photocarrier grating under diferents condition. The a-SI:h is a reactive new semiconductor with an outstanding potenciality for applications. It is an excellent photoconductor material produced in thin-film forms. Nowadays it has been used in large scale in solar cells, big area photosensor and thin-¬film transistor. Although its production is simple, the formation process of the thin-films is complex and empirical. Therefore the value of the transport and kinetic properties of this material is essential as a reference of quality of the produced material.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18593号 / 工博第3954号 / 新制||工||1608(附属図書館) / 31493 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 伊藤 紳三郎, 教授 木村 俊作, 教授 辻井 敬亘 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

This thesis treats about semiconducting silicon structures. It describes the characteristics of the element and creation of P and N type of semiconductor and discusses about different types of faults in the crystal lattice. It deals with the description of methods for monitoring faults in semiconductor ie. determining the properties of semiconductors via EBIC, EBIV and CC methods, which are used for analysis of semiconductor devices and materials. Determining the properties of silicon components is being done by generation of charge carriers in the sample loaded in chamber of the scanning electron microscope by high energy electrons. Bellow the sample surface is being generated an electric charge which is being collected by probes. Using this data obtained by EBIC and CC were evaluated diffusion length and lifetime of electrons.

No description available.