Herein, we report the first solution-processed broadband photodetectors to break the past compromise between sensitivity and speed of response. Specifically, we report photodiodes having normalized detectivity (D*) > 1012 Jones and a 3dB bandwidth of > 2.9 MHz. This finding represents a 170,000 fold improvement in response speed over the most sensitive colloidal quantum dot (CQD) photodetector reported1 and a 100,000 fold improvement in sensitivity over the fastest CQD photodetector reported2. At the outset of this study, sensitive, solution-processed IR photodetectors were severely limited by low response speeds1. Much faster response speeds had been demonstrated by solution-processed photodetectors operating in the visible3, but these devices offered no benefits for extending the spectral sensitivity of silicon. No available solution-processed photodetector combined high sensitivity, high operating speed, and response to illumination across the UV, visible and IR. We developed a fast, sensitive, solution-processed photodetector based on a photodiode formed by a Schottky barrier to a CQD film. Previous attempts to form sensitive photodetectors based on CQD photodiodes had demonstrated low quantum efficiencies that limited sensitivity4,5. Efficient, sensitive semiconductor photodiodes are based on two fundamental characteristics: a large built-in potential that separates photogenerated charge carriers and minimizes internal noise generation, and high semiconductor conductivity for efficient collection of photogenerated charge. Schottky barriers to CQD films were developed to provide high, uniform built-in potentials. A multi-step CQD ligand exchange procedure was developed to allow deposition of tightly packed films of CQDs with high mobility and sufficiently well-passivated surfaces to form high-quality metallurgical junctions. The temporal response of the CQD photodiodes showed separate drift and diffusion components. Combined with detailed measurements of the Schottky barrier, these characteristics provided the physical basis for a numerical model of device operation. Based on this understanding, devices that excluded the slow diffusive component were fabricated, exploiting only the sub-microsecond field-driven transient to achieve MHz response bandwidth. These devices are the first to combine megahertz-bandwidth, high sensitivity, and spectral-tunability in photodetectors based on semiconducting CQDs. Record performance is achieved through advances in materials and device architecture based on a detailed understanding the physical mechanisms underlying the operation of CQD photodiodes.

Herein, we report the first solution-processed broadband photodetectors to break the past compromise between sensitivity and speed of response. Specifically, we report photodiodes having normalized detectivity (D*) > 1012 Jones and a 3dB bandwidth of > 2.9 MHz. This finding represents a 170,000 fold improvement in response speed over the most sensitive colloidal quantum dot (CQD) photodetector reported1 and a 100,000 fold improvement in sensitivity over the fastest CQD photodetector reported2. At the outset of this study, sensitive, solution-processed IR photodetectors were severely limited by low response speeds1. Much faster response speeds had been demonstrated by solution-processed photodetectors operating in the visible3, but these devices offered no benefits for extending the spectral sensitivity of silicon. No available solution-processed photodetector combined high sensitivity, high operating speed, and response to illumination across the UV, visible and IR. We developed a fast, sensitive, solution-processed photodetector based on a photodiode formed by a Schottky barrier to a CQD film. Previous attempts to form sensitive photodetectors based on CQD photodiodes had demonstrated low quantum efficiencies that limited sensitivity4,5. Efficient, sensitive semiconductor photodiodes are based on two fundamental characteristics: a large built-in potential that separates photogenerated charge carriers and minimizes internal noise generation, and high semiconductor conductivity for efficient collection of photogenerated charge. Schottky barriers to CQD films were developed to provide high, uniform built-in potentials. A multi-step CQD ligand exchange procedure was developed to allow deposition of tightly packed films of CQDs with high mobility and sufficiently well-passivated surfaces to form high-quality metallurgical junctions. The temporal response of the CQD photodiodes showed separate drift and diffusion components. Combined with detailed measurements of the Schottky barrier, these characteristics provided the physical basis for a numerical model of device operation. Based on this understanding, devices that excluded the slow diffusive component were fabricated, exploiting only the sub-microsecond field-driven transient to achieve MHz response bandwidth. These devices are the first to combine megahertz-bandwidth, high sensitivity, and spectral-tunability in photodetectors based on semiconducting CQDs. Record performance is achieved through advances in materials and device architecture based on a detailed understanding the physical mechanisms underlying the operation of CQD photodiodes.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Graphene is widely considered to be a promising candidate for a new generation of electronics, but there are many outstanding fundamental issues that need to be addressed before this promise can be realized. This thesis focuses on the production and properties of graphene grown epitaxially on the carbon terminated face (C-face) of hexagonal silicon carbide leading to the construction of a novel graphene transistor structure. C-face epitaxial graphene multilayers are unique due to their rotational stacking that causes the individual layers to be electronically decoupled from each other. Well-formed C-face epitaxial graphene single layers have exceptionally high mobilities (exceeding 10,000 cm^2/Vs), which are significantly greater than those of Si-face graphene monolayers. This thesis investigates the growth and properties of C-face single layer graphene. A field effect transistor based on single layer graphene was fabricated and characterized for the first time. Aluminum oxide or boron nitride was used for the gate dielectric. Additionally, an all graphene/SiC Schottky barrier transistor on the C-face of SiC composed of 2DEG in SiC/Si2O3 interface and multilayer graphene contacts was demonstrated. A multiple growth scheme was adopted to achieve this unique structure.

Thesis (Ph.D.)--University of Western Australia, 2006.

Thesis (Ph. D.)--University of Hong Kong, 1994. / Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 138-143). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 138-143). Also available on the Internet.

Orientador: José Alexandre Diniz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-18T16:42:08Z (GMT). No. of bitstreams: 1 Lima_LucasPetersenBarbosa_M.pdf: 10518299 bytes, checksum: abe557fa5f682bd296c9fb416948d523 (MD5) Previous issue date: 2011 / Resumo: Filmes de nitreto de titânio (TiN) e nitreto de tântalo (TaN) foram depositados sobre substratos de Si (100) utilizando um sistema de sputtering reativo, com diferentes fluxos de N2 (10-80 sccm) e potência (500-1500W), em ambiente de N2/Ar. Foram analisadas as influências da mistura gasosa N2/Ar e potência nas propriedades estruturais e elétricas dos filmes de TiN e TaN, utilizando as técnicas de perfilometria, microscopia de força atômica, 4 pontas, espectroscopia Raman, difração de raios-x e espectroscopia de fotoelétron. As análises físicas e elétricas dos filmes de TiN e TaN demonstram que os filmes são policristalinos, com as orientações preferenciais (311)-( 111) e (200)-( 111), respectivamente. Os valores das taxas de deposições, resistividades elétricas e tamanho de grão para os filmes de TiN e TaN estão entre 4 e 78 nm/min, 150 e 7500 ??.cm e 0,001 e 0,027 ?m2, respectivamente. Foram fabricados capacitores MOS e diodos Schottky com eletrodos superiores de TiN e TaN com dielétricos de SiOxNy ou SiO2, e extraídas curvas CV e IV destes dispositivos, para extração de parâmetros como tensão de flatband (VFB), densidade de carga efetiva (Q0/q) e função trabalho do eletrodo superior (WF). As curvas CV dos capacitores MOS com dielétrico de SiOxNy e eletrodo superior de TiN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 cm2, 0,29 V e 4,65 eV, respectivamente, que são compatíveis com a tecnologia CMOS. As curvas CV dos capacitores MOS com dielétrico de SiOxNy e eletrodo superior de TaN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 cm2, 1,36 V e 3,81 eV, respectivamente, que não são compatíveis com a tecnologia CMOS. As curvas CV dos capacitores MOS com dielétrico de SiO2 e eletrodo superior de TiN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 e 1012 cm2, de 0,12 V e 0,36 V, e, 4,15 eV e 4,43 eV, respectivamente, que são compatíveis com a tecnologia CMOS. As curvas CV dos capacitores MOS com dielétrico de SiO2 e eletrodo superior de TaN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 e 1012 cm2, 0,29 V e 0,20 V, e, 4,41 eV e 4,44 eV, respectivamente, que são compatíveis com a tecnologia CMOS. Estes resultados indicam que os filmes de TiN e TaN são compatíveis para serem utilizados em dispositivos da tecnologia MOS / Abstract: Tantalum nitride (TaN) and titanium nitride (TiN) films have been obtained by DC sputtering, using different nitrogen flow (10 - 80 sccm) and power (500 - 1500 W), in a nitrogen (N2)/argon (Ar) ambient on Si (100) substrates. The N2/Ar ratio in gas mixture and power effects on structural and electrical properties of TaN and TiN films were investigated by scan profiler (film thickness and deposition rate), atomic force microscopy (rms roughness and grain size), fourprobe technique (electrical resistivity), Raman spectroscopy, x-ray diffraction (crystal orientation) and X-ray photoelectron spectroscopy (film composition). The physical and structural analyses of TiN and TaN films show that TiN and TaN films were polycrystalline, with (311)-( 111) and (200)-( 111) preferred orientation, respectively. The deposition rates, electrical resistivities and grain size values of TiN and TaN films were between 4 and 78 nm/min, 150 and 7500 ??.cm and 0,001-0,027 ?m2, respectively. MOS capacitors and Schottky diodes were fabricated with TiN and TaN as upper electrodes and dielectrics with SiOxNy or SiO2. CV and IV measurements were carried out on these devices and flatband voltage (VFB), effective charge density (Q0/q) and metal gate work function (WF) were extracted from these measurements. The extracted values of Q0/q, VFB e WF 1010 cm2, 0,29 V e 4,65 eV, and these values were extracted from CV curves of MOS capacitors with TiN as gate electrode and SiOxNy as gate dielectric. The extracted values of Q0/q, VFB e WF 1010 cm2, 1,36 V e 3,81 eV, and these values were extracted from CV curves of MOS capacitors with TiN as gate electrode and SiOxNy as gate dielectric. The extracted values of Q0/q, VFB and WF were about 1010 and 1012 cm2, 0,12 V and 0,36V, and 4,15 eV and 4,43 eV, and these values were extracted from CV curves of MOS capacitors with TiN as gate electrode and SiO2 as gate dielectric. The extracted values of Q0/q, VFB and WF were about 1010 and 1012 cm2, 0,29 V and 0,20V, and 4,41 eV and 4,44 eV, and these values were extracted from CV curves of MOS capacitors with TaN as gate electrode and SiO2 as gate dielectric. These extracted values for VFB and WF indicates that the TiN and TaN films are suitable for MOS technology / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19829号 / エネ博第335号 / 新制||エネ||67(附属図書館) / 32865 / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 松田 一成, 教授 佐川 尚, 教授 大垣 英明 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM