NSF/ENG/ECCS-BSF: Semiconductor Polytype Heterostructures: A Pathway to Superior Power Electronics

非技术描述：该项目旨在为电子、半导体多型异质结构开发一种新的构建模块，该异质结构由相邻的晶格匹配材料层组成，仅在其原子堆叠顺序上不同。半导体多型异质结构有望形成极化掺杂的二维电子气体，具有高载流子浓度和高载流子迁移率，从而实现超高导电性；因此，它们有望为晶体管速度近十年的停滞提供及时的解决方案。该项目为研究生、本科生和高中生提供培训，让他们参与密歇根大学和本-古里安大学的合作。该合作将美国研究人员的专业知识（半导体多型薄膜和异质结构的分子束外延和晶体学表征）与以色列研究人员的专业知识（多型异质结构的光谱表征和高电子迁移率晶体管的制造/表征）整合在一起。获得的新知识将通过出版物和演讲以及研究生和本科生课程的发展广泛传播。外联活动强调对妇女和代表性不足的少数民族的指导。技术描述：该项目寻求新的理解ZB与WZ多型选择和ZB/WZ多型异质结构的电子态/输运性质，从而为多型异质结构的制造策略提供信息。利用原位反射高能电子衍射（RHEED）、多光束光学应力传感和扫描隧道显微镜，将实时监测外延过程中表面重建、多型选择和局部电子态之间的相互作用。除了研究生长动力学外，还将探讨静电现象（包括热和电子感应充电）对偏爱ZB （GaAs）和偏爱WZ （GaN）材料中WZ和ZB多型选择的影响。使用卷积神经网络的机器学习方法将用于量化和分类RHEED模式，从而加速识别适当的生长动力学和诱导表面电荷的过程，以选择WZ和ZB多型。在外延之后，将使用高分辨率和扫描透射电子显微镜，选择区域和会聚束电子衍射以及x射线衍射来检查界面结构和极性。电子态将使用扫描隧道光谱和基于Franz-Keldysh效应的光学光谱工具进行检查。在确定关键生长动力学和/或静电现象以定制多型选择之后，将制备用于hemt的ZB/WZ多型异质结构。这项工作的预期结果包括确定薄膜外延过程中选择ZB或WZ多型的多型策略，以及ZB/WZ多型HEMT结构的设计和制造，这将有助于发现新的晶体管策略，具有超越摩尔定律的逻辑和存储器集成的潜力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical Description: This project aims to develop a new building block for electronics, semiconductor polytype heterostructures, which consist of adjacent layers of lattice-matched materials differing only in their atomic stacking sequences. Semiconductor polytype heterostructures are expected to result in the formation of a polarization-doped two-dimensional electron gas, with both high carrier concentration and high carrier mobility, resulting in ultra-high conductivity; thus, they are expected to offer a timely solution to a near-decade plateau in transistor speed. The project provides training to graduate, undergraduate, and high school students, engaging them in a collaboration between the University of Michigan and Ben-Gurion University. The collaboration integrates the expertise of the U.S. investigators (molecular-beam epitaxy and crystallographic characterization of semiconductor polytype films and heterostructures) with that of the Israeli investigators (spectroscopic characterization of polytype heterostructures and fabrication/characterization of high-electron mobility transistors). The new knowledge gained will be broadly disseminated through publications and presentations, and graduate and undergraduate curriculum development. Outreach activities emphasize the mentoring of women and underrepresented minorities.Technical Description: The project seeks new understanding ZB vs. WZ polytype selection and the electronic states/transport properties of ZB/WZ polytype heterostructures, thereby informing strategies for fabrication of polytype heterostructures. The interplay between surface reconstruction, polytype selection, and local electronic states will be monitored in real-time during epitaxy using in-situ reflection high-energy electron diffraction (RHEED), multi-beam optical stress sensing, and scanning-tunneling microscopy. In addition to examining growth kinetics, the influence of electrostatic phenomena, including thermal and electron-induced charging, on WZ vs. ZB polytype selection in both ZB-preferring (GaAs) and WZ-preferring (GaN) materials will be explored. A machine-learning approach using convolutional neural networks will be used to quantify and classify RHEED patterns, thereby accelerating the process of identifying appropriate growth kinetics and induced surface charging to select WZ vs. ZB polytypes. Following epitaxy, the interface structure and polarity will be examined using high-resolution and scanning transmission electron microscopy, selected-area and convergent-beam electron diffraction, and x-ray diffraction. The electronic states will be examined using scanning tunneling spectroscopy and optical spectroscopic tools based upon the Franz-Keldysh effect. Upon identification of the key growth kinetics and/or electrostatic phenomena to tailor polytype selection, ZB/WZ polytype hetero-structures for HEMTs will be fabricated. Expected outcomes of this work include the identification of strategies for polytype selection during epitaxy of thin films that prefer the ZB or WZ polytype, as well as the design and fabrication of ZB/WZ polytype HEMT structures that will facilitate the discovery of new strategies for transistors, with the potential for integration of logic and memory beyond Moore's Law.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.