Dilute Nitride AlGaNP/GaP for Solid-State Lighting

技术：本项目旨在加深对绿色到琥珀色光谱区域（~ 540nm至~ 610nm波长）固态光源的基本理解和量子效率的提高。该方法涉及研究材料系统，在GaP上生长的AlGaNP，预期结果是更好的材料性能和更简单的固态照明加工技术。该方法由三个部分组成：琥珀色发光GaNP/GaP led生长、加工和优化的基础材料科学问题的研究，与AlInGaP/GaAs led的比较，探索AlGaNP/GaP的绿色发射，以及制造绿色发光AlGaNP/AlGaP led并与InGaN/GaN led进行比较。相关的物理性质，如有效质量、波段对准和光学性质，将被系统地研究。众所周知，InGaN led的量子效率随着波长从蓝色增加到绿色而降低，因为随着In浓度的增加，材料质量会降低。AlInGaP led的量子效率随着波长从红色到琥珀色的减小而降低，因为波段排列接近II型阶梯排列，导致发光强度降低。在理论指导下，选择了AlGaNP-on-GaP材料体系作为led在这一“色隙”区域发光的材料体系，因为它具有以下潜在优势：1)在透明的gap衬底上，除了有源区域外，具有全透明的层结构，可以最大限度地提取光；2)与蓝宝石或SiC上晶格不匹配的InGaN/GaN相比，由于GaP衬底上的晶格匹配或伪晶结构，预计会有较低的螺纹位错密度；3)具有比蓝宝石和GaAs更高导热系数的衬底（GaP）（分别为1.1 vs. 0.35和0.55 W cm-1 K-1）；4) AlInGaP/AlInP的导电带和价带偏置比AlInGaP/AlInP高3倍，载流子约束更强，具有更好的高温特性；5)更高的产量和更低的成本，因为同样的功率需要更小的尺寸（芯片可以做得更小，每片晶圆的产量增加，降低了每片成本）；6)更简单，成本效益高的一步外延，而不是AlInGaP led所需的衬底去除和晶圆键合，或者在蓝宝石或SiC上生长InGaN/GaN。非技术：该项目涉及材料科学主题领域的基础研究问题，具有很高的技术相关性。该研究将在基础水平上为电子器件的新理解和能力贡献基础材料科学知识。该计划的一个重要特点是通过培养学生在一个基础和技术上重要的领域的研究和教育的整合。这些研究活动将促进研究生在新型化合物半导体、LED器件设计、制造和测试的生长和表征方面的跨学科培训，并提供书面和口头报告准备方面的培训。本科学生将从麦克奈尔计划（McNair Program）等渠道招募，该计划为低收入学生和/或代表性不足的少数民族提供服务。本科生将有机会从事高级表征工作，如原子力显微镜，并参加加州大学圣地亚哥分校的本科生研究会议。此外，PI将参加COSMOS（加州州立数学与科学暑期学校）住宿暑期项目，其中一组高中学生将参加一个LED项目，使用商用LED和在该项目中制造的固态照明实验。

Technical: This project aims for greater fundamental understanding and improved quantum efficiency of solid state light emitters in the green-to-amber spectral region (~540 nm to ~610 nm wavelength). The approach involves investigating the material system, AlGaNP grown on GaP, with outcomes anticipated of better material properties and simpler processing technologies for solid state lighting. The approach consists of three parts: investigation of fundamental materials science issues involved in the growth, processing, and optimization of amber emitting GaNP/GaP LEDs, comparison with AlInGaP/GaAs LEDs, exploring AlGaNP/GaP for green emission, and fabricating green emitting AlGaNP/AlGaP LEDs and comparing with InGaN/GaN LEDs. Relevant physical properties, such as effective mass, band alignment, and optical properties, will be systematically investigated. It is well known that the quantum efficiency of InGaN LEDs decreases as the wavelength increases from blue to green because material quality degrades as the In concentration increases. The quantum efficiency of AlInGaP LEDs decreases as the wavelength decreases from red to amber because the band alignment approaches a type II, staircase lineup, resulting in reduced luminescence intensity. With theoretical guidance, the material system, AlGaNP-on-GaP, was chosen for LEDs emitting in this "color gap" region because of its potential advantages: 1) maximum light extraction because of an all-transparent layer structure, except the active region, on a transparent GaP substrate; 2) low threading dislocation density expected because of a lattice-matched, or pseudomorphic, structure on a GaP substrate, in contrast to lattice-mismatched InGaN/GaN on sapphire or SiC; 3) a substrate (GaP) with higher thermal conductivity than sapphire and GaAs (1.1 vs. 0.35 and 0.55 W cm-1 K-1, respectively); 4) better high-temperature characteristics because of stronger carrier confinement from larger conduction-band and valence-band offset, which are 3 times those of AlInGaP/AlInP; 5) higher yield and lower cost because a smaller size is needed for the same power (chips can be made smaller and the yield per wafer increased, reducing cost per chip); 6) simpler, cost-effective one-step epitaxy, instead of substrate removal and wafer bonding needed for AlInGaP LEDs, or heteroepitaxial growth of InGaN/GaN on sapphire or SiC.Non-Technical: The project addresses basic research issues in a topical area of materials science having high technological relevance. The research will contribute basic materials science knowledge at a fundamental level to new understanding and capabilities in electronic devices. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. The research activities will promote interdisciplinary training of graduate students in growth and characterization of novel compound semiconductors, LED device design, fabrication and testing, and provide training in preparation of written and oral presentations. Undergraduate students will be recruited from sources such as the McNair Program, which serves low-income students and/or underrepresented minorities. Undergraduate students will have the opportunity to work on advanced characterizations, such as atomic force microscopy, and participate in undergraduate research conferences at UCSD. Additionally, the PI will participate in the COSMOS (California State Summer School for Mathematics and Science) residential summer program, where a team of high school students will participate in an LED project using commercial LEDs and those fabricated in this program for solid-state lighting experiments..