Dilute Nitride AlGaNP/GaP for Solid-State Lighting

技术支持：该项目旨在对固态发光体在绿色至琥珀色光谱区域（~540 nm至~610 nm波长）的量子效率有更深入的了解。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。该方法包括三个部分：琥珀色发光GaNP/GaP LED的生长、加工和优化中涉及的基本材料科学问题的研究，与AlInGaP/GaAs LED的比较，探索AlGaNP/GaP的绿色发光，以及制作绿色发光AlGaNP/AlGaP LED并与InGaN/GaN LED进行比较。相关的物理性质，如有效质量，能带排列和光学性质，将进行系统的研究。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，因为材料质量随着In浓度增加而降低。AlInGaP LED的量子效率随着波长从红色降低到琥珀色而降低，因为能带排列接近II型阶梯排列，导致发光强度降低。在理论指导下，选择AlGaNP-on-GaP材料系统用于在该“色隙”区域中发射的LED，因为其潜在的优点：1）由于在透明GaP衬底上的除有源区之外的全透明层结构，光提取最大化; 2）由于GaP衬底上的晶格匹配或赝晶结构而预期的低穿透位错密度，与蓝宝石或SiC上晶格失配InGaN/GaN形成对比; 3）具有比蓝宝石和GaAs更高热导率的衬底（GaP（分别为1.1与0.35和0.55 W cm-1 K-1）;（4）导带和价带偏移量是AlInGaP/AlInP的3倍，导带和价带偏移量大，载流子限制更强，高温特性更好; 5）更高的产量和更低的成本，因为对于相同的功率需要更小的尺寸（芯片可以做得更小，每个晶片的产量增加，降低了每个芯片的成本）; 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片键合，或者在蓝宝石或SiC上异质外延生长InGaN/GaN。该项目涉及具有高度技术相关性的材料科学专题领域的基础研究问题。该研究将为电子设备的新理解和能力提供基础材料科学知识。该计划的一个重要特点是通过在一个基本和技术上重要的领域对学生进行培训来整合研究和教育。研究活动将促进研究生在新型化合物半导体的生长和表征，LED器件设计，制造和测试方面的跨学科培训，并提供书面和口头报告准备方面的培训。本科生将从麦克奈尔计划（McNair Program）等来源招募，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先进的表征工作，如原子力显微镜，并参加UCSD的本科生研究会议。此外，PI将参加COSMOS（加州数学和科学暑期学校）的住宅夏季计划，其中一组高中生将参加一个使用商用LED的LED项目，以及在该计划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..