Exploring ultra-wide bandgap ambipolar transparent conducting semiconductors for deep ultraviolet optoelectronic devices

半导体激光二极管是广泛的消费和工业产品的重要组成部分。激光二极管的基本结构包括p型和n型半导体薄膜。N型和p型半导体中的大多数载流子是电子和空穴，它们可以分别视为带负电荷的粒子和带正电荷的粒子。一旦该设备与电池等能源连接，电子和空穴就会在结合处相遇并重新结合以发光。发射波长在可见光和红外范围内的光的半导体激光器已经被广泛使用。相比之下，在UV-B和UV-C波段(特别是波长小于315纳米)波长较短的半导体激光器严重不发达。这是因为通常被称为超宽带隙半导体的半导体，如氮化铝镓，本应在这些光谱带内发光，但并没有可靠地用强p型材料制造。这项拟议的研究通过开发一种新的超宽带隙半导体镁镓氧化物来应对这一挑战，该半导体将被掺杂到n型和p型中。PI和学生们将生长、制造和表征基于这些新材料的发光器件和激光器，目标是展示发射波长在200至270纳米之间的深紫外光半导体激光器。这些深紫外光半导体激光器在深空通信、环境监测、导弹和火焰探测、信息存储和记录、病毒消毒和水净化、光动力学医学诊断、治疗和外科手术等方面有着重要的应用。作为努力的一部分，该项目将培训研究生和本科生，并让这些学生从代表不足的少数族裔进入工程学。此外，在当地高中生参观加州大学河滨分校工程学院一年一度的“发现日”活动期间，将计划为他们提供与该项目密切相关的主题的学习课程，并将为一些高中生提供暑期研究机会，为他们参加科学博览会做准备。本项目旨在展示第一个用于深紫外光光子学的带隙大于4.9 eV的双极型超宽带隙透明导电半导体。这项研究是基于PI小组最近发现的超宽带隙镁镓氧化物(MgGaO)是一种强p型透明导电氧化物半导体而计划的。该项目将全面研究超宽带隙氧化镁、可控p型和n型掺杂的氧化镁、氧化镁/氧化锌(X：Mg，Al)异质结以及它们的光电子器件。该项目将使用分子束外延来合成这些半导体，并将使用各种表征技术来阐明它们的结构、电学和光学性质。通过霍尔效应、光致发光、X-射线光电子能谱等表征手段，揭示了掺镁氧化镁的p型和n型掺杂的起源，制备了波长小于270 nm的深紫外光半导体激光器、发光二极管(LED)和光电探测器。这一结果将是半导体波导激光器发射波长跨越当前边界的重要一步，目前半导体波导激光器的发射波长已投入商业使用，这是一项重要的进步，将在许多基于技术的领域带来巨大的经济机会。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。

Semiconductor laser diodes are an important component in a wide range of consumer and industrial products. The basic structure of a laser diode contains p- and n-type semiconductor thin film layers. Majority carriers in n- and p-type semiconductors are electrons and holes, which can be regarded as negatively and positively charged particles, respectively. Once the device is connected with an energy source such as a battery, the electrons and holes meet in the junction and recombine to emit light. Semiconductor lasers emitting light with a wavelength in the visible and infrared ranges have been widely available. In contrast, semiconductor lasers with shorter wavelength in the ultraviolet-B and ultraviolet-C bands (specifically with wavelength less than 315 nanometers) are severely underdeveloped. This is because the semiconductors commonly known as ultra-wide bandgap semiconductors such as aluminum gallium nitride, which are supposed to emit light in these spectral bands, have not been made with strong p-type material reliably. The proposed research addresses this challenge by developing a new ultra-wide bandgap semiconductor magnesium gallium oxide, which will be doped into both n-type and p-type. The PI and students will grow, fabricate and characterize light emitting devices and lasers based on these novel materials with a goal of demonstrating deep ultraviolet semiconductor laser devices with emission wavelengths between 200 and 270 nanometers. These deep ultraviolet semiconductor lasers have important applications in deep space communication, environmental monitoring, missile and flame detection, information storage and recording, virus disinfection and water purification, photodynamic medical diagnosis, therapy, and surgery, and so on. As a part of the effort, this project will train graduate and undergraduate students and involve these from underrepresented minorities to engineering. In addition, learning sessions on the subject closely related to the project will be planned for local high school students during their visit to the annual event “Discovery Day” at the College of Engineering, UC Riverside, and summer research opportunities will be provided to some high schoolers to prepare them for science fairs. This project seeks to demonstrate the first ambipolar ultra-wide bandgap transparent conducting semiconductor with bandgap of larger than 4.9 eV for deep-ultraviolet photonics. The research is planned based on the PI group’s recent finding that ultra-wide bandgap magnesium gallium oxide (MgGaO) is a strong p-type transparent conducting oxide semiconductor. The project will comprehensively study ultra-wide bandgap MgGaO, controllable p- and n-type doping of MgGaO, MgGaO/XGaO (X: Mg, Al) heterostructures, and their optoelectronic devices. The project will synthesize these semiconductors using molecular beam epitaxy and will elucidate their structural, electrical and optical properties using various characterization techniques. The origin of the p- and n-type doping of MgGaO will be revealed through detailed characterizations including Hall effect, photoluminescence, x-ray photoelectron spectroscopy, etc. Deep-ultraviolet semiconductor lasers, light emitting diodes (LEDs) and photodetectors with wavelengths less than 270 nm will be fabricated and characterized. The result will be an important step across the current boundary for the emission wavelength of semiconductor waveguide lasers, currently 375 nm in commercial use – an important advance that will enable significant economic opportunities in many technology-based domains.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.