具有复合垒层结构的InGaN/(In)GaN多量子阱结构设计和外延生长研究

GaN-base blue and green laser diodes (LDs) is widely used in laser display and laser lightening, which has attracted great attentions from researchers worldwide. The active region of traditional GaN-based LDs consists of InGaN/GaN multiple quantum wells (MQWs), which requires relatively high indium content to achieve blue and green lasing. However, the relatively high indium content in MQWs will degrade the material quality, weaken the thermal stability and enhance the polarization field in MQWs, which will deteriorate the properties and reliability of LDs. In this proposal, we put forward a novel InGaN/(In)GaN MQWs structure. By inserting thin InGaN layers with low indium content between the quantum wells and quantum barriers, the effective confinement barrier height of quantum well would be reduced, thus the quantum levels would be lowered according to quantum mechanics. Therefore, the emission wavelength of MQWs would extend to longer wavelength region. The newly-designed InGaN/(In)GaN MQWs may help to significantly reduce the indium content, improve the material quality and weaken the polarization field of active region of blue and green LDs. Focusing on the important issues such as engineering the quantum levels and wavefunctions of electron and hole, we would design proper MQW structure with low indium content and high quantum efficiency. By controlling the stress and defect generation during MOCVD epitaxy, We could achieve novel MQWs with high material quality. Combining structure design and epitaxy growth optimization, the blue and green LDs withhigh performance and high reliability could be finally obtained.

GaN基蓝绿光激光器在激光显示和激光照明等领域具有广阔的市场前景，是当前的研究热点。传统GaN基激光器有源区采用的InGaN/GaN多量子阱结构，需要较高的In组分以实现蓝光和绿光激射。较高的In组分会引起量子阱材料质量差、热稳定性差、极化电场强等问题，严重影响激光器的性能和可靠性。本项目提出了一种新型InGaN/(In)GaN多量子阱结构，通过在量子阱和量子垒之间插入低组分的InGaN薄层，降低量子限制势垒高度，从而降低阱中的量子能级，实现发光波长向长波长方向延伸。该新型有源区结构有望明显降低激光器量子阱中的In组分，显著提高量子阱材料质量和热稳定性，减小量子阱中的极化电场。本项目将重点研究量子能级和电子空穴波函数调控的规律和方法，对新型量子阱结构进行优化设计；研究生长过程中的应力、缺陷的变化规律和调控方法，实现高质量新型量子阱结构生长；最终实现高性能、高可靠性的GaN基蓝绿光激光器。

氮化镓（GaN）基激光器作为一种重要的发光器件，在激光照明、激光显示领域具有广阔应用的前景，其中的蓝光和绿光激光器与已成熟的铝镓铟磷（AlGaInP）基红光激光器共同组成了红、绿、蓝三基色，是激光显示技术的核心器件。目前，先进GaN基激光器制造技术只掌握在日本日亚（Nichia）、日本索尼（Sony）、德国欧司朗（Osram）等少数公司手中。虽然国内GaN激光器研究已经取得了一些进展，但尚不能满足激光显示等高端应用的要求。随着激光显示和激光照明市场的快速增长，对自主知识产权的GaN基激光器的需求变得极为迫切。.当前，限制激光器性能提升的重要因素是有源区材料质量。针对传统InGaN/GaN量子阱发光波长和量子效率等问题，人们进行了许多尝试，提出了诸多新的量子阱结构，如阶梯形量子阱、三角形量子阱、delta-AlGaN量子阱、InGaN-delta-InN量子阱等。这些结构虽然可以增加电子空穴波函数重叠，提升量子速率，但是无法对发光波长进行有效调控，量子阱所需的In组分仍然较高。本项目针对常规量子阱In组分高、材料质量差、热稳定性差、极化电场强等问题，提出了一种新型的复合垒层InGaN/(In)GaN多量子阱结构，与传统InGaN/GaN量子阱不同，该结构在InGaN量子阱和GaN量子垒之间插入InGaN薄层，具有以下优点: （1）大幅降低量子阱中的量子能级，有效延伸发光波长或降低量子阱In组分。（2）实现电子和空穴量子能级分别调控。（3）增加量子阱的热稳定性。（4）降低量子阱极化电场。综上所述，本项目提出的具有复合垒层结构的InGaN/(In)GaN多量子阱，有望明显延伸发光波长、降低量子阱In组分和极化电场，提高材料质量和温度稳定性。然而，量子阱限制势垒的降低除了会引起波长延伸外，还有可能导致电子空穴波函数向垒中穿透，使量子阱发光效率降低；InGaN层的插入会使含In材料的整体厚度增加，可能导致V形坑、失配位错及其它点缺陷的产生。因此，本项目将围绕新型InGaN/(In)GaN量子阱的量子能级和波函数调控、应力和缺陷控制等关键科学问题，重点研究量子阱结构设计，以及高质量量子阱材料生长等内容，最终实现量子阱In组分降低和激光器性能提升。