This study investigated the mobility and trapping of charges and the recombination of x-ray induced charges in a-Se. X-ray induced changes in these parameters were also examined. Prior to exposure to x-rays, the mobilities and deep trapping lifetimes of both holes and electrons were constant. Exposure to x-rays caused no change in the mobility of these charges. Immediately following exposure, the hole deep trapping lifetime would fall ~30% while the electron deep trapping lifetime would only change ~10%. The deep trapping lifetimes continued to change unpredictably several hours after the initial exposure. Following an extended rest period, the charge lifetimes within the a-Se film would return to a stable state, but not necessarily equal to the initial lifetime prior to the x-ray exposure. These changes were proposed to occur because of a relaxation or reordering of the atoms in a-Se, similar to accepted changes thought to occur resulting from exposure to visible light. Analysis of the experimental evidence suggests that intimate valence alternation pair (IVAP) charged defects are created by x-ray irradiation. These defects are relatively unstable, disappearing within two hours after irradiation. Since the hole and electron lifetimes continued to change for at least 12 hours, it was concluded that the traditional view of deep charge trapping into IVAP defects cannot be dominant. A new charge trapping theory, consistent with published optically induced effects, is proposed in this work to explain these observations. The energy required to create a free electron-hole pair in a-Se by exposure to x-rays was measured. This energy was found to exhibit a strong field and temperature dependence, with little dependence on the mean x-ray beam energy. These findings are consistent with the geminate recombination theory, generally agreed to be the dominant charge loss mechanism with optical photons in a-Se. The persistent x-ray photocurrent was found to be thermally activated below ~250 K with an activation energy of 0.16 eV. This does not correspond to the energy level of any known traps in a-Se, and lends further support to the charge trapping theory developed earlier.

A theory of the carrier transport, optical emission, and photoconductivity from optoelectronic devices based on ambipolar long-channel carbon-nanotube (CNT) field-effect transistors (FETs) is presented in this dissertation. In optical emitters based on ambipolar long-channel CNT FETs, an analytic diffusive-transport model for various recombination mechanisms is provided for the first time. The relationship and the scaling of emitted light-spot size and emitted optical power are clearly depicted for the first time as well. We also implement a numerical diffusive-transport approach for the light emission, in which the focus is on the effects of radiative and nonradiative recombination in the channel, with the movement of the spatial recombination profile in response to the gate and drain voltages. For the first time, we find that the emitted light-spot size and the emitted optical power depend sensitively on the operative nonradiative recombination mechanisms. We implement a numerical diffusive-transport approach including exciton photogeneration as well for photoconductors based on ambipolar long-channel CNT FETs with uniform and near-field photoexcitation. We show that the photocurrents are typically much smaller than the dark currents, and explain some possible reasons. Moreover, the exciton densities in CNTs are calculated and the effect of exciton diffusion is presented.

GaSe thin films were deposited by thermal evaporation technique with and without Cd doping. X-ray analysis showed that the crystallinity increases in (1014) preferred orientation direction with annealing for doped and undoped films. The room temperature conductivity and mobility values of the samples were found to be for doped and undoped films in between 1.3&times / 101 - 3.4&times / 102 (&amp / #8486 / -cm)-1, 1.2&times / 10-6 - 1.5&times / 10-6 (&amp / #8486 / -cm)-1 and 5.9 &amp / #8211 / 20.9 (cm2/V.s) (for doped samples only), respectively. Due to the high resistivity of the undoped samples mobility measurements could not be performed. The dominant conduction mechanisms were determined to be thermionic emission in the high temperature region (250-400 K), tunneling in the range 160-250 K and between 100-150 K variable range hopping mechanism for the doped films. For the undoped films above 250 K thermionic emission was the dominant conduction mechanism. Space charge limited currents in parallel and perpendicular directions of the film surface showed two different localized energy levels with different concentrations for each case, namely, 99.8 meV with concentration 3.5&times / 1012 cm-3 and 418.3 meV with the concentration 2.2&times / 105 cm-3 for parallel direction and for perpendicular direction 58.3 meV with concentration 6.2&times / 1025 cm-3 and 486.1 meV with concentration 3.3&times / 1022 cm-3. Photocurrentillumination intensity dependences indicated that power exponent of illumination intensity with values n&gt / 1 implied two recombination centers exist in studied samples.

Thesis (M.S.)--West Virginia University, 1998. / Title from document title page. "December 1998." Document formatted into pages; contains viii, 125 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 84-89).

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Wanting leaves 220-226 Conclusions and recommendations. Typescript. Vita. Includes bibliographical references (leaves [339]-342). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Wanting leaves 220-226 Conclusions and recommendations. Typescript. Vita. Includes bibliographical references (leaves [339]-342). Also available on the Internet.

Thesis (Ph. D.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains ix, 72 p. : ill. Includes abstract. Includes bibliographical references (p. 68-72).

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A high resolution photoconductivity investigation of two 13 -3 photon magneto-absorption (TPMA) in n-InSb (n - 9 x 10 cm ) has been performed. This is the first time that two-photon absorption in a semiconductor has been studied with cw lasers only. With a stable cw CC>2 laser and a highly sensitive sampling and magnetic field modulation technique, a minimum of 4 2 transitions in the TPMA photoconductivity spectra can be observed. Most of these transitions are a result of the usual spherical approximation TPMA selections rules (An =0, ±2; As = 0 for e ⊥ B and Δn = 0; Δs = 0 for e || B) . However, some transitions, in particular several near the TPMA band edge, are not explained by these rules. The TPMA spectra have been found to depend upon crystallographic orientation. This has not been previously observed. The temperature variation of the fundamental energy gap Eg between 2 and 100° K is also obtained from TPMA experiments.

Submitted by Lucas Augusto Moisés (lucasaugustomoises@hotmail.com) on 2018-11-12T14:28:19Z No. of bitstreams: 1 Dissertação Lucas Augusto Moisés_2.pdf: 2728995 bytes, checksum: 4372fefa9820f84b2816df79babc8610 (MD5) / Approved for entry into archive by Adriana Aparecida Puerta null (dripuerta@rc.unesp.br) on 2018-11-13T18:12:17Z (GMT) No. of bitstreams: 1 moises_la_me_rcla.pdf: 2728995 bytes, checksum: 4372fefa9820f84b2816df79babc8610 (MD5) / Made available in DSpace on 2018-11-13T18:12:18Z (GMT). No. of bitstreams: 1 moises_la_me_rcla.pdf: 2728995 bytes, checksum: 4372fefa9820f84b2816df79babc8610 (MD5) Previous issue date: 2018-09-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No presente trabalho produziram-se filmes finos transparentes de ZnO depositados pela técnica de spray-pirólise com objetivo de estudar o comportamento de suas propriedades elétricas durante a incidência de luz UV e após a incidência de luz (no escuro). Para tal, foram propostos três designs experimentais do tipo fatorial de dois níveis, um do tipo fatorial fracionário com base no modelo de Plackett-Burman e dois fatoriais completos. Na realização desses experimentos, variou-se parâmetros de produção do filme e também parâmetros experimentais no momento da realização da medida, sendo nove parâmetros no total. Através dos dados obtidos nesses experimentos, obteve-se respostas experimentais. Em cima disso foram realizadas analises estatísticas. Assim, através dessas análises se conheceu quais os fatores experimentais tiveram maior influência em cada uma dessas respostas e os resultados obtidos tiveram um bom acordo com a teoria, indicando a eficácia dos experimentos fatoriais de dois níveis realizados. Por fim, foi realizado medidas de predição e comparado as respostas obtidas nessas medidas com os dados estatísticos obtidos. Através dessa comparação, foi encontrado uma resposta reprodutível, indicando assim a possibilidade aplicação de filmes de ZnO na área de sensores / In the present work, transparent thin films of ZnO deposited by the spray - pyrolysis technique were used to study the behavior of their electrical properties during the incidence of UV light and after the incidence of light (in the dark). For that, three experimental designs of the two - level factorial type were proposed, one of the fractional factorial type based on the Plackett - Burman model and two complete factorials. In the performance of these experiments, parameters of production of the film were varied as well as experimental parameters at the moment of the measurement, being nine parameters in total. Through the data obtained in these experiments, experimental responses were obtained. Statistical analyzes were performed on top of this. Thus, through these analyzes it was known which experimental facto rs had the greatest influence on each one of these responses and the results obtained had a good agreement with the theory, indicating the effectiveness of the two - level factorial experiments performed. Finally, prediction measures were performed and the r esponses obtained in these measurements were compared with the statistical data obtained. Through this comparison, a reproducible response was found, thus indicating the possibility of applying ZnO films in the area of sensors