Collaborative Research: Non-Conventional Etching and MOCVD Regrowth for Beta-GaO/AlGaO 3D HEMTs

氧化镓是一种很有前途的半导体材料，可用于尺寸缩小和性能提高的电子器件，特别是在高压、高温和高频元件中的应用。基于这种新型半导体材料的材料开发和器件制造都还处于起步阶段。该项目探索材料生长和器件加工，以实现高度可扩展的射频器件，其性能超过基于其他半导体材料(如硅、氮化镓或碳化硅)的当前器件技术。该项目致力于解决由于这种氧化物半导体的复杂原子结构而在蚀刻和材料生长过程中不断增加的挑战。了解刻蚀的基本机制和材料生长过程对于充分利用这一新兴材料系统所提供的优势至关重要。这项研究的成功实施有望为电子行业提供知识基础，并对美国经济产生积极影响。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。拟议的教育计划侧重于研究和教育的整合、课程开发和学生培训。建议中的研究成果将提供鼓舞人心的教材和实验室项目，为我们的下一代劳动人口提供拥抱新兴技术的培训。该项目培养了两名高级半导体材料合成、材料表征和器件设计与制造领域的研究生。首席调查员致力于通过创造包容的环境、积极指导和以身作则，促进包括妇女在内的人数不足的群体参与科学和工程领域。拟议的外联活动的重点是高中女生和教师。这两家私人投资机构将继续积极领导或参与现有的教育和推广计划，包括NSF本科生研究经验(REU)和教师研究经验(RET)计划、当地和IEEE女性工程计划。氧化镓(Ga2O；GaO)具有高击穿场强，是一种超越碳化硅和氮化镓的新兴超宽带隙半导体。这项研究的目的是展示一种三维GaO/AlGaO高电子迁移率晶体管(HEMT)，该沟道由非传统的无损伤各向异性刻蚀技术(Meta-Assisted Chemical etch；MacEtch)和金属有机化学气相沉积(MOCVD)外延AlGaO外延再生长形成。研究范围包括：i)利用非破坏性MacEtch技术实现高深宽比的Ga2O33D沟道结构；ii)在MacEtch制作的非平面Ga2O结构上发展MOCVD生长、掺杂和AlGaO的再生长；iii)对MacEtted Ga2O表面和再生的GaO/AlGaO异质界面进行化学、结构、光学和电学表征；以及iv)展示具有非平面3D沟道的GaO/AlGaO HEMTs。所提出的GaO/AlGaO HEMT结构具有非平面的三维拓扑结构和复杂的单斜晶系结构，为探索晶体取向相关的刻蚀、生长速率、AlGaO组分、GaO/AlGaO界面缺陷以及掺杂/杂质掺杂提供了一个独特的平台。该项目的学术意义将建立对Ga2O_3的MacEtch中载流子的产生和质量传输特性作为金属催化剂图案的函数及其与表面取向、晶体掺杂浓度、紫外光照射波长和强度的对准以及宽禁带氧化物半导体的一般刻蚀机制的基本理解。表面和界面表征将提供对空位和其他缺陷陷阱的影响和限制因素的洞察，并为不同的器件架构要求建立控制流程。除了拟议的计划外，将探索的平台和创新概念还可以用于许多其他类型的设备，以实现尺寸扩展和性能增强，包括光电子器件，如日盲紫外线(UV)探测器和高温火焰传感器。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Gallium oxide represents a promising semiconductor material for electronic devices concerning size scaling and performance enhancement especially for applications in high voltage, high temperature, and high frequency components. Both materials development and device fabrication based on this new semiconductor material is still at its infancy. This project explores the material growth and device processing to achieve a highly scalable radio frequency device with performance beyond the current device technology based on other semiconductor materials such as silicon, gallium nitride or silicon carbide. This project seeks to address the rising challenges in the etching and material growth process due to the complex atomic structure of this oxide semiconductor. Understanding of the fundamental etching mechanisms and materials growth process is critical to fully utilize the advantages offered by this emerging material system. A successful execution of this research is expected to provide a knowledge foundation to electronics industry with positive impacts on the US economy. The research is integrated with educational activities and outreach to benefit the broader community. The proposed education plans focus on integration of research and education, curriculum development, and student training. The results obtained from the proposed research will provide inspiring teaching materials and laboratory projects, to provide training of our next generation workforce for embracing emerging technologies. This project trains two graduate students in the areas of advanced semiconductor materials synthesis, material characterization, and device design and fabrication. The principal investigators (PIs) are strongly committed to promoting the participation of underrepresented groups including women in science and engineering, by creating an inclusive environment, active mentoring, and leading by examples. The proposed outreach activities focus on high school girls and teachers. Both PIs will continue to actively lead or be involved in existing education and outreach programs including the NSF Research Experience for Undergraduates (REU) and Research Experience for Teachers (RET) programs, local and IEEE Women in Engineering programs.Gallium oxide (Ga2O3; GaO), with high breakdown field strength, represents an emerging ultrawide bandgap semiconductor beyond silicon carbide and gallium nitride. The goal of the proposed research is to demonstrate a three-dimensional (3D) GaO/AlGaO high electron mobility transistor (HEMT) using a 3D channel formed by a non-conventional damage-free anisotropic etching technique (meta-assisted chemical etch; MacEtch) followed by metalorganic chemical vapor deposition (MOCVD) epitaxial regrowth of AlGaO. The scope of the research includes: i) realizing high aspect ratio Ga2O3 3D channel structures using the non-destructive MacEtch technology; ii) developing MOCVD growth, doping, and regrowth of AlGaO on the MacEtch-produced non-planar Ga2O3 structures; iii) characterizing the MacEtched Ga2O3 surfaces and the regrown GaO/AlGaO hetero-interfaces chemically, structurally, optically, and electrically; and iv) demonstrating GaO/AlGaO HEMTs with non-planar 3D channels. The proposed GaO/AlGaO HEMT structure, with the non-planar 3D topology and the complex monoclinic crystal structure, provides a unique platform to explore the crystal orientation dependent etching, growth rate, AlGaO composition, GaO/AlGaO interface defects, and dopant/impurity incorporation. The intellectual significance of the project will establish fundamental understanding of the carrier generation and mass transport properties in MacEtch of Ga2O3 as a function of metal catalyst pattern and its alignment with surface orientation, crystal doping concentration, and ultra-violet light illumination wavelength and intensity, as well as the etching mechanism for wide bandgap oxide semiconductors in general. Surface and interface characterization will provide insights in the contributing and limiting factors in vacancy and other defects related traps and establish control process for different device architecture requirements. Beyond the proposed program, the platform and innovative concepts to be explored can also be used for many other types of devices for size scaling and performance enhancement, including optoelectronics devices such as solar blind ultraviolet (UV) detectors and high temperature flame sensors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.