Structure and Properties of AlN and InN Surfaces and Defects

技术：尽管氮化物半导体材料正被用于一些电子和光子应用，包括异构场效应晶体管和蓝光发射器，但缺陷、杂质和表面问题正在阻碍新的应用，例如用于紫外光发光二极管和激光器的铝含量越来越高的AlGaN合金，以及用于太赫兹发射器的InN基晶体管的开发。该项目旨在通过紧密耦合的实验和计算工作来解决这些材料科学问题。高质量的AlN、InN和它们的合金是外延生长的，高质量的样品能够使用结构、电气和光学技术对表面、点缺陷和杂质进行详细的表征。对表面电子聚集层进行了研究和控制。N型和p型掺杂的极限将被推进。实验工作直接与基于密度泛函理论的最先进的第一原理计算相联系；将通过使用最近成功实施的技术来解决“带隙问题”，例如准粒子计算和混合泛函。研究了缺陷和杂质的深(局域)能级和浅(扩展)能级，以及表面重构和表面态。关闭理论和实验结果之间的循环有望提供对与这些新材料的合成和加工相关的基本原子水平机制和现象的深入理解。非技术性：该项目解决具有高度技术相关性的材料科学主题领域的基础研究问题。作为研究重点的宽带隙半导体被认为是可见光和紫外光发射器的主要材料，向固态照明的过渡将对发达国家和发展中国家产生巨大影响。氮化物也开始在高频设备领域取得进展，应用于电信和雷达。另一个潜在影响很大的领域是光伏，其中氮化物材料系统可以跨越从紫外线到红外的范围。这个项目具有重要的教育价值：研究生参与了理论和实验之间的紧密合作。此外，该计算项目还将利用加州大学伯克利分校加利福尼亚纳米系统研究所全新的全能球体设备。阿洛球体是一个3层楼高的球形空间，在其中可以体验到完全身临其境的互动虚拟环境。它将有助于可视化和理解各种材料中的波函数和成键环境，以及向广大受众传播结果。

Technical: Although nitride semiconductor materials are being used in some electronic and photonic applications including heterostructure field-effect transistors and blue light emitters, defects, impurities, and surface issues are hampering new applications such as the use of increasingly higher aluminum content AlGaN alloys for ultraviolet light emitting diodes and lasers and the development of InN-based transistors for terahertz emitters. This project aims to address these materials science issues through a tightly coupled experimental and computational effort. High quality AlN, InN, and their alloys are grow epitaxially and the high quality samples enable detailed characterization of surfaces, point defects, and impurities using structural, electrical, and optical techniques. Electron accumulation layers on the surface are investigated and controlled. The limits of n-type and p-type doping will be pushed. The experimental effort is directly tied to state-of-the-art first-principles calculations based on density functional theory; the "band-gap problem" will be addressed through the use of techniques that have recently successfully been implemented, such as quasi-particle calculations and hybrid functionals. Deep (localized) and shallow (extended) levels of defects and impurities are investigated, as well as surface reconstructions and surface states. Closing the loop between theoretical and experimental results is expected to provide deep understanding of fundamental atomic-level mechanisms and phenomena associated with synthesis and processing of these novel materials.Non-technical: This project addresses basic research issues in a topical area of materials science with high technological relevance. The wide-band-gap semiconductors that are the focus of the investigation are recognized as the prime materials for light emitters throughout the visible and into the ultraviolet, and the transition to solid-state lighting will have tremendous impact both in the developed as well as the developing world. Nitrides are also starting to gain ground in the area of high-frequency devices, with applications in telecommunications and radar. Another area of high potential impact is for photovoltaics, where the nitride materials systems can span the range from ultraviolet to infrared. This project has significant educational value: the graduate students are involved in a tight collaboration between theory and experiment. In addition, the computational project will make use of the brand new Allosphere facility at the California Nanosystems Institute at UCSB. The Allosphere is a 3-story-high spherical space in which a fully immersive and interactive virtual environment can be experienced. It will be helpful with the visualization and understanding of wave functions and bonding environments in the various materials, as well as with the dissemination of results to a broad audience.