Infrared photonics using ferroelectric scandium-aluminum nitride semiconductors

非技术描述本项目研究在传统氮化物半导体中掺入钪所带来的独特的电学和光学性质。这些材料使新型光源和探测器可用于从化学传感和医疗诊断到电力电子和能量收集的实际应用。这项研究工作包括用计算机模拟进行材料设计，合成超纯无缺陷半导体，以及结构和光学材料表征。该项目还将材料研究与教育和外联活动结合起来，旨在增加所有年龄的学生在传统课堂内外的学习机会。参与该项目的研究人员和学生参加了在内部或在当地学校组织的外联活动，以增加K-12学生和普通公众在有趣的、以项目为导向的环境中接触材料科学的现代科学主题。为普渡大学的中学夏令营“物理内幕”设计了教案，并制作了物质基本光学性质的实验演示。为了最大限度地提高高中水平的影响力，这些活动邀请教师进行暑期研究。特别是，教师们正在制定基于探究的教案，将与量子科学相关的概念纳入高中课程。研究人员还为Hoosier科学教师协会的年度会议设计了带回家的材料的动手活动。技术描述该项目的主要目标是建立纤锌矿ScAlN作为一种可行的光子平台，用于新颖的红外应用。该项目利用铁电ScAlN独特的固有特性，并在设计的结构内进一步操纵它们，以促进光谱的近红外范围的利用。特别是，利用近晶格匹配的ScAlN/GaN异质结的导带中量子态之间的光学跃迁来扩展器件产生、检测和调制红外光的能力。III-氮化物半导体具有独特的电子特性，使其适合于将半导体器件的功能提高到目前其他材料系统无法达到的光谱范围。这种创新的方法使用了新兴的光子材料SC-Al-氮化物，以缓解与应变有关的问题，这些问题过去阻碍了氮化物光子学进入红外领域。研究工作是跨学科的，涉及材料设计和生长、结构表征和光学表征。通过大量的能带结构计算，设计了ScAlN/GaN异质结。为了获得最高的材料纯度和原子结构的单层控制，采用等离子体辅助分子束外延在高质量的准体GaN衬底上生长了含Sc的材料。一个中心任务是确定满足近红外光学工艺施加的最严格要求的外延生长条件。为了将半导体材料的微观结构与光学和电学性质联系起来，用高分辨率X射线衍射、像差校正的透射电子显微镜和原子探针层析对半导体材料的结构进行了全面的表征。用傅里叶变换红外光谱和光致发光光谱对材料的能带结构进行了实验研究。这项研究有助于对子带间光学跃迁和非线性光学过程的物理基础的理解。这些红外材料有望立即使发射器和光电探测器具有当前技术无法比拟的功能(更宽的光谱范围、更高的速度和更好的温度性能)。它们也是光子集成电路以及与硅电子单片集成的理想候选者。片上二次谐波的成功产生为差频产生和参数下转换等其他非线性过程开辟了新的途径。此外，新型含Sc半导体在电子(如高电子迁移率晶体管)、紫外线、热电、压电和等离子设备等方面的其他应用也是有益的。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。

Nontechnical descriptionThis project investigates the unique electronic and optical properties brought about by incorporation of scandium into traditional nitride semiconductors. These materials enable novel light sources and detectors that can be used in practical applications ranging from chemical sensing and medical diagnostics to power electronics and energy harvesting. The research effort involves material design with computer simulations, synthesis of ultra-pure defect-free semiconductors, as well as structural and optical material characterization. This project also combines material research with educational and outreach activities that aim to increase learning opportunities for students of all ages, inside and outside the traditional classroom. The investigators and students involved in this project participate in outreach activities organized either in-house or at local schools to increase exposure of K-12 students and the general public to modern scientific topics in materials science in a fun, project-oriented environment. Lesson plans are designed and experimental demonstrations of basic optical properties of matter are built for the middle-school summer camp “Physics Inside Out” at Purdue. To maximize impact at the high-school level, the activities engage teachers in summer research. In particular, the teachers are developing inquiry-based lesson plans incorporating concepts related to quantum science into the high-school curriculum. The researchers also design hands-on activities with take-home materials for the annual meeting of the Hoosier Association of Science Teachers.Technical descriptionThe principal objective of this project is to establish wurtzite ScAlN as a viable photonic platform for novel infrared applications. This project exploits the unique native properties of ferroelectric ScAlN and further manipulates them within designed structures to facilitate utilization of the near-infrared range of the spectrum. In particular, optical transitions between quantized states in the conduction band of near lattice-matched ScAlN/GaN heterostructures are utilized to expand device capabilities to generate, detect, and modulate infrared light. III-nitride semiconductors have unique electronic properties that make them suitable for advancing the functionality of semiconductor devices into spectral ranges currently inaccessible with other material systems. The innovative approach employs the emergent photonic material Sc-Al-nitride to mitigate strain-related issues that have impeded progress of nitride photonics into the infrared in the past. The research effort is interdisciplinary and involves material design and growth, structural characterization, and optical characterization. ScAlN/GaN heterostructures are designed using extensive band-structure calculations. To achieve maximum material purity and monolayer-control of the atomic structure, the Sc-containing materials are grown by plasma-assisted molecular beam epitaxy on high quality quasi-bulk GaN substrates. A central task is to identify the epitaxial growth conditions that satisfy the most stringent requirements imposed by near-infrared optical processes. To correlate microstructure with optical and electronic properties, the structure of the semiconductor materials is comprehensively characterized with high-resolution x-ray diffraction, aberration-corrected transmission electron microscopy, and atom-probe tomography. The band structure of the materials is probed experimentally with Fourier transform infrared spectroscopy and photoluminescence. The research contributes to the fundamental understanding of the physics of intersubband optical transitions and nonlinear optical processes. These infrared materials are expected to immediately enable emitters and photodetectors with functionality unmatched by current technologies (wider spectral range, higher speeds, and better temperature performance). They are also ideal candidates for photonic integrated circuits as well as monolithic integration with Si electronics. Successful second-harmonic generation on chip opens avenues for other nonlinear processes such as difference frequency generation and parametric down-conversion. Moreover, the novel Sc-containing semiconductors are beneficial for other applications in electronic (e.g. high-electron mobility transistors), ultraviolet, thermoelectric, piezoelectric, and plasmonic devices.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.