Ultrawide Bandgap Gallium Oxide: Fundamental Understanding From Materials Synthesis to Devices

非技术描述：氧化镓是一种很有前途的材料，用于雷达和通信系统、风力涡轮机和轨道牵引中的高压、高温和高频部件。其约4.9电子伏特的带隙和估计的高击穿电压大大超过了目前开发的材料，如GaN和4H-SiC，同时仍具有半导体特性。本论文主要研究了用于预测氧化镓基本材料性能的理论模型，以及以高纯金属镓和氧气为源的氧化镓材料的实验合成。该项目旨在生产高质量的氧化镓，并促进对这种新兴材料的基本了解。对材料中缺陷基本性质的理论研究为实验材料生长和材料表征提供了指导。制定合成这种材料的战略并在了解其性质方面取得进展，为研究基础设施提供了重要的工作。这项研究的成功实施有望为电力电子行业提供知识基础，并对美国经济产生积极影响。该项目培养了两名高级半导体材料合成、材料表征、第一性原理建模和器件技术领域的研究生。这项研究与教育活动和外联活动相结合，使更广泛的社区受益。技术描述：主要研究目标是确定和解决合成高质量超宽带隙(UWBG)氧化镓的基本材料挑战，以推动下一代大功率电子学和短波长光电子学的发展。氧化镓的合成和基本认识仍处于起步阶段。由于需要考虑三个不同的氧位置和两个不同的镓位置，因此对空位、间隙、反位和杂质或有意掺杂等本征缺陷的探索预计将是复杂的。研究小组通过将第一性原理模型与一种新的合成方法相结合来研究这些问题，以获得高质量的外延氧化镓薄膜。具体来说，研究工作包括：(I)用低压化学气相沉积方法生长氧化镓；(Ii)通过在离轴衬底上生长氧化镓来减少缺陷和提高材料质量；(Iii)计算点缺陷、候选掺杂和缺陷复合体的形成能和缺陷能级，以及它们的实验特征，如电子顺磁超精细和g张量以及光学性质；(Iv)研究晶体缺陷对氧化镓电学性质的影响。这个项目提供了对电子结构、声子、输运、缺陷和生长优化的基本了解。理论研究将有助于确定特定缺陷能级的化学性质，从而为实验材料合成和材料表征提供指导。该项目的成果将填补该领域的知识空白，并为该材料系统的未来应用奠定基础。

Nontechnical description: Gallium oxide is a promising material for high-voltage, high-temperature, and high-frequency components in radar and communication systems, wind turbines, and rail traction. Its band gap of ~4.9 electron volts and estimated high breakdown voltage significantly goes beyond currently developed materials, such as GaN and 4H-SiC, while still presenting semiconductor properties. This research focuses on the theoretical modeling of gallium oxide for predicting its fundamental material properties, and the experimental synthesis of this material by using high purity metallic gallium and oxygen as sources. The project aims to produce high quality gallium oxide and to advance the fundamental understanding of this emerging material. Theoretical studies of the fundamental properties of imperfections in the material provides guidance for experimental material growth and material characterization. The development of strategies for synthesis of this material and progress in understanding their properties contribute an important body of work to the research infrastructure. A successful execution of this research is expected to provide a knowledge foundation to power electronics industry with positive impacts on the US economy. This project trains two graduate students in the areas of advanced semiconductor materials synthesis, material characterization, first-principles modeling and device technologies. The research is integrated with educational activities and outreach to benefit the broader community. Technical description: The key research goal is to identify and address the fundamental material challenges of synthesizing high quality ultra-wide-band-gap (UWBG) gallium oxide to advance the next generation high power electronics and short wavelength optoelectronics. The synthesis and fundamental understanding of gallium oxide is still very much in its infancy. The exploration of native defects such as vacancies, interstitials, antisites, and impurities or intentional dopants is expected to be complex because three different oxygen sites and two different gallium sites need to be considered. The research team investigates these problems by combining first-principles modeling with a proposed novel synthesis method for achieving high quality epitaxial gallium oxide films. Specifically, the research efforts include: (i) a low pressure chemical vapor deposition approach to grow gallium oxide; (ii) reduce defects and improve material quality by growing gallium oxide on off-axis substrates; (iii) calculations of the energy of formation and defect levels for point defects, candidate dopants and defect complexes and their experimental signatures, such as electron paramagnetic hyperfine and g-tensors and optical properties; (iv) investigate the crystal defects on electrical properties of gallium oxide. This project provides fundamental understanding of electronic structure, phonons, transport, defects and growth optimization. The theoretical studies will assist in identifying the chemical nature of specific defect levels and thereby will provide guidance for experimental material synthesis and material characterization. The results from this project will fill the knowledge gap in this field, and build a foundation for future applications of this material system.