Controlling Conductivity in the UV-Transparent Conducting Oxide Ga2O3

技术：该重点研究小组项目由电子和光子材料（EPM）和陶瓷（CER）项目共同资助，包括系统的跨学科努力，结合物理学，材料科学和电气工程，阐明透明导体氧化镓（Ga2O3）的结构，电子和光学特性之间的相互联系，重点是内在和外在缺陷，界面化学和维度。Ga2O3在整个太阳光谱和近紫外（UV）中是透明的，带隙为4.9 eV（波长~ 250 nm），但可以通过掺杂（例如Si或Sn），通过加工产生固有缺陷（例如氧空位或间隙）或通过深紫外光吸收来实现导电。β - Ga2O3的各向异性晶体结构包含固有的、一维的、开放的通道，并且可以制成任意维度的结构——三维块状晶体、二维薄膜、准一维纳米带、一维纳米线和0D纳米球——并且当与Al2O3合金在很宽的浓度范围内保持这种结构。Ga2O3可以通过适当的处理进行电阻开关（RS），但与更常见的过渡金属氧化物不同，镓在产生氧空位和/或间隙时保留Ga3+，将其置于不同类别的RS材料中。该项目将解决与Ga2O3相关的关键问题，这些问题目前还没有得到很好的理解：Ga2O3中离子和电子电导率之间的相互作用，表面和界面反应诱导电导率变化的纳米级过程，以及内在通道结构在控制这些特性中的作用。Ga2O3已经提出了几种应用，包括“太阳盲”透明导体，电阻开关存储器元件，仅紫外光电探测器，化学传感器和催化衬底。这项研究将有助于对控制这些原型装置结构运行的电导率和界面还原氧化反应的机理理解，从而使其功能得到改进和增强。非技术：这个项目在几个层次上处理劳动力发展。研究生将积极参与跨科学和工程的多学科研究，并涉及美国和日本的学术，工业和政府实验室之间的合作。他们将在几个领域发展关键技能，这将增加他们的职业机会：材料合成、桌面样品表征、同步加速器和其他基于用户设施的测量、理论建模和提案写作（用于用户设施访问），以及分析和口头和书面沟通技巧，因为他们处理、解释和展示他们的研究成果。该项目还包括定义明确的活动，以增加与经常不知道华盛顿大学研究活动的人群的互动。与当地一所高中建立联系，大多数学生通常不打算上大学，通过积极指导高中生对根据该提案培养的氧化物样品进行光电流测量，与指导那里的科学和机器人俱乐部的高中老师进行夏季研究合作，以及访问教室讨论我们的科学和学生的职业和教育选择，将扩大与该高中的联系。

Technical: This Focused Research Group project, funded jointly by the Electronic and Photonic Materials (EPM) and Ceramics (CER) Programs, encompasses a systematic interdisciplinary effort combining physics, materials science and electrical engineering to elucidate interconnections among the structural, electronic and optical properties of the transparent conductor gallium oxide, Ga2O3, with emphasis on intrinsic and extrinsic defects, interface chemistry, and dimensionality. Ga2O3 is transparent throughout the solar spectrum and into the near ultraviolet (UV), with a band gap of 4.9 eV (wavelength ~ 250 nm), but can be made conductive through doping (e.g., Si or Sn), by processing to create intrinsic defects (e.g. oxygen vacancies or interstitials), or through deep-UV photoabsorption. The anisotropic crystal structure of beta- Ga2O3 contains intrinsic, one-dimensional, open channels, and can be fabricated in structures with arbitrary dimensionality - 3D bulk crystals, 2D films, quasi-1D nanobelts, 1D nanowires and 0D nanospheres - as well as maintain that structure when alloyed with Al2O3 over a wide concentration range. Ga2O3 can undergo resistive switching (RS) with appropriate processing, but unlike more commonly considered transition metal oxides, gallium remains Ga3+ during creation of oxygen vacancies and/or interstitials, placing it in a different class of RS materials. This project will address key issues related to Ga2O3 that are not currently well understood: the interplay between ionic and electronic conductivity in Ga2O3, the nanoscale processes by which surface and interface reactions induce conductivity changes, and the role of the intrinsic channel structure in governing these properties. Ga2O3 has been proposed for several applications, including a "solar-blind" transparent conductor, a resistive switching memory element, an UV only photodetector, a chemical sensor, and a catalysis substrate. This research will contribute to mechanistic understanding of the conductivity and interface reduction-oxidation reactions that govern the operation of these prototype device structures, enabling refinement and enhancement of their function.Non-Technical: This project addresses workforce development at several levels. Graduate students will be actively involved in multidisciplinary research that spans science and engineering, and involves collaboration among academic, industrial and government laboratories in the US and Japan. They will develop key skills across several arenas that will enhance their career opportunities: materials synthesis, table-top sample characterization, synchrotron and other user-facility-based measurements, theoretical modeling, and proposal writing (for user facility access), as well as analytical and both oral and written communication skills as they process, interpret and present their research findings. The project also includes well-defined activities to increase interactions with populations that are frequently unaware of research activities at the University of Washington. Established connections with a local high school at which the majority of students don't typically aim for college will be expanded through active mentoring of high school students to perform photocurrent measurements of oxide samples grown under this proposal, summer research collaboration with the high school teacher who directs the science and robotics clubs there, as well as visits to classrooms to discuss both our science and students career and educational options.