Mechanisms of Optical Transitions in AlGaN Alloys and GaN/Al GaN Quantum Wells

本项目研究GaN/AlGaN量子阱（QW）结构中的光学跃迁和载流子动力学；高AlN摩尔分数AlGaN涂层的光学跃迁机理以及体积减小和光约束对GaN微结构（包括微盘、棱镜和金字塔）光学和光电子特性的影响。皮秒时间分辨光致发光将用于研究各种iii -氮化物样品和结构中的光学跃迁机制，并与其他表征技术相结合，提供样品晶体质量、纯度、合金成分和量子阱界面特性的信息。重点将放在高AlN摩尔分数的AlGaN上。此外，由于许多基于iii -氮化物的应用利用了异质结和多量子阱（MQW）， AlGaN/GaN和AlxGa(1-x)N/AlyGa(1-y)N（y x）异质结和MQW结构以及合金中从GaN （Eg=3.4 eV）到A1N （Eg=6.2 eV）的带隙可调性将被探索，以更好地理解与这些材料相关的基本深紫外（UV）光电现象。将研究MBE和MOCVD合成的材料。研究工作将解决影响选择性和横向生长的特性，包括晶体取向和缓冲层。将研究量子阱厚度、势垒层中掺杂浓度、AlGaN层中的合金成分以及生长后的加工条件，以评估AlGaN合金中的n型和p型掺杂、缺陷能级、自补偿以及AlGaN中深层杂质的形成。结构表征包括TEM， AFM， SEM和x射线分析；SIMS，光谱学和霍尔效应测量将用于评估成分和电性能。%%%

This project addresses optical transitions and carrier dynamics in GaN/AlGaN quantum well (QW) structures; mechanisms of optical transitions in AlGaN epilayers with high AlN mole fractions; and effects of reduced volume and optical confinement on the optical and optoelectronic properties of GaN microstructures including micro-disks, prisms, and pyramids. Picosecond time-resolved photoluminescence will be used to study the mechanisms of optical transitions in a variety of III-nitride samples and structures, and, in conjunction with additional characterization techniques, to provide information on sample crystalline quality, purity, alloy composition, and quantum well interface properties. Emphasis will be placed on AlGaN with high AlN mole fractions. Additionally, since many III-nitride based applications take advantage of heterojunctions and multiple quantum wells (MQW), AlGaN/GaN and AlxGa(1-x)N/AlyGa(1-y)N(y x) heterojunction and MQW structures and the tunability of the bandgap in the alloys from GaN (Eg=3.4 eV ) to A1N (Eg=6.2 eV) will be explored for achieving greater understanding of fundamental deep ultraviolet (UV) optoelectronic phenomena associated with these materials. Materials synthesized by both MBE and MOCVD will be studied. Research efforts will address properties which affect selective and lateral growth including crystallographic orientation as well as buffer layers. Quantum well thickness, doping concentration in the barrier layers, alloy composition in the AlGaN layers, and post-growth processing conditions will be studied to assess n- and p- type doping in AlGaN alloys, defect energy levels, self-compensation, and the formation of deep level impurities in AlGaN. Structural characterization includes TEM, AFM, SEM and X-ray analyses; SIMS, optical spectroscopy, and Hall effect measurements will be used to assess compositional and electrical properties.%%%