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型半导体薄膜层。n型和p型半导体中的大多数载流子是电子和空穴，它们可以分别看作带负电和带正电的粒子。一旦该装置与电池等能源连接，电子和空穴就会在连接处相遇并重新组合发光。半导体激光器发射波长在可见光和红外线范围内的光已经广泛使用。相比之下，在紫外- b和紫外- c波段波长较短的半导体激光器（特别是波长小于315纳米的激光器）则严重不发达。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，应该在这些光谱带内发光，但还没有可靠地用强p型材料制成。提出的研究通过开发一种新的超宽带隙半导体氧化镁镓来解决这一挑战，该半导体将被掺杂成n型和p型。PI和学生将基于这些新材料生长，制造和表征发光器件和激光器，目标是展示发射波长在200到270纳米之间的深紫外半导体激光器件。这些深紫外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、光动力医学诊断、治疗和手术等方面具有重要应用。作为努力的一部分，该项目将培训研究生和本科生，并将这些未被充分代表的少数民族纳入工程领域。此外，在加州大学河滨分校工程学院参加一年一度的“发现日”活动期间，将为当地高中生安排与该项目密切相关的主题学习课程，并为一些高中生提供暑期研究机会，为他们参加科学展览做准备。该项目旨在展示第一个双极超宽带隙透明导电半导体，其带隙大于4.9 eV用于深紫外光子学。该研究计划基于PI小组最近的发现，即超宽带隙氧化镁镓（MgGaO）是一种强p型透明导电氧化物半导体。本项目将全面研究超宽带隙MgGaO、可控p型和n型掺杂MgGaO、MgGaO/XGaO （X: Mg, Al）异质结构及其光电器件。该项目将利用分子束外延合成这些半导体，并将利用各种表征技术阐明它们的结构、电学和光学特性。通过霍尔效应、光致发光、x射线光电子能谱等详细表征，揭示了p型和n型MgGaO掺杂的来源。将制备并表征波长小于270 nm的深紫外半导体激光器、发光二极管和光电探测器。该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，目前用于商业用途的半导体波导激光器发射波长为375 nm，这是一个重要的进步，将在许多基于技术的领域带来重大的经济机会。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。

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.