低铟组分InGaN量子阱中载流子泄漏的抑制及GaN基近紫外激光器研究

Based on the significance of short-wavelength laser diodes in many fields, such as solid-state lighting, biochemical detection, laser fuse and material processing, this proposal concentrates on the theoretical design and device fabrication of GaN-based laser diodes in near-ultraviolet region. Compared with blue and green region, the indium content of InGaN quantum well in this wavelength region decreases to a relatively low value. As a result, the exciton localization state density originating from the In composition fluctuation in InGaN quantum well correspondingly decreases. The quantum confinement effect of carriers is thus weakened in GaN/InGaN multiple quantum well (MQW) active region and vertical electron leakage from active region to p-type region is correspondingly enhanced. In order to address this problem, the project is focusing on mechanisms and possible solutions about how to enhance the quantum confinement effect of carriers in InGaN quantum wells simultaneously with the suppression of vertical electron leakage, including increasing In composition fluctuation to increase exciton localization state density, replacing GaN quantum barrier with quaternary (Al, In)GaN layer to raise the band offset and barrier height in (Al, In)GaN/InGaN MQW, introducing more In content in AlInGaN quantum wells to increase exciton localization state density, improving (Al, In)GaN/(Al)InGaN interface abruptness to reduce the adverse impact of interface states on radiation recombination in quantum wells, changing the polarization field in AlInGaN electron blocking layer to eliminate the energy band bending effect. Some other solutions to the key problems in GaN-based ultraviolet laser diodes, such as the p-type doping, are also proposed to adapt the special wavelength and device structure in near-ultraviolet region. With the project approval and implementation, the stimulated emission of GaN-based laser diodes in near-ultraviolet region with peak wavelength <400 nm and peak power >5 W will be realized under electrical injection.

本课题针对固态照明、生化探测、激光引信和材料加工等重大科技领域中对半导体短波长激光器的迫切需求，重点解决在近紫外波段InGaN量子阱中In组分减少导致的局域态密度降低、对阱内载流子限制作用变弱、有源区载流子泄漏增强的问题，研究阱内量子限制作用的增强机制并对载流子泄漏进行抑制，包括增强阱内In组分分布的不均匀性以提高局域态密度，用(Al, In)GaN代替GaN作为垒层以提高势垒高度，在AlInGaN四元合金量子阱中掺入更多的In组分以提高局域态密度，提高多量子阱的界面陡峭度来降低界面态对复合发光的影响，采用极化反转电子阻挡层抑制电子泄漏等；同时结合紫外波段的有源区结构特点和激光器研制的需要，对p型掺杂等科学问题进行研究，最终实现波长小于400 nm GaN基近紫外激光器的电注入激射，脉冲峰值功率达到5 W，为国家提供核心的半导体近紫外光源。

GaN基近紫外激光器在多个领域具有重要应用前景。在固态照明中，紫外波段荧光粉转换效率高，显色指数高，颜色稳定；紫外光激发的荧光分析技术可应用于光谱分析和生化制剂检测；紫外激光本身具有波长短、散射强、光子能量高的特点，可以作为激光引信和工业加工的光源。. 本课题的研究目标是针对近紫外激光器有源区中InGaN量子阱铟组分较低的特点，从量子阱结构上研究阱内载流子受到量子限制作用的增强机制和有源区内电子泄漏的抑制方法，并从实际外延过程中对InGaN量子阱进行生长调控，降低激光器阈值并提高有源区的发光复合效率，实现GaN激光器在<400nm近紫外波段的电注入激射，脉冲峰值功率达到5W。. 通过基金委的支持和课题组成员四年来的工作，我们超额完成了本课题的研究目标，具体如下：.（1）采用同温生长模式、调整生长温度曲线等方法对低铟组分InGaN紫外量子阱的局域态进行调控，改善了量子阱的发光效率；通过波导层和电子阻挡层的设计减小了光学吸收损耗，抑制了电子泄漏电流；通过抑制碳杂质的补偿效应实现了高效p型掺杂，提高了激光器的注入效率。.（2）在解决量子阱局域态调控、光学吸收损耗和电子泄漏电流抑制等材料外延生长和激光器结构设计等关键科学问题的基础上，研制出我国第一支GaN基紫外激光器，阈值电流密度为1.6-2.0kA/cm2，激射波长为392-395nm，连续激射输出光功率可达80mW。将激射波长进一步降低至380nm波段，实现了激射波长为382nm的紫外激光器的室温连续激射，阈值电流密度为2.8kA/cm2。.（3）通过提高InGaN紫外量子阱的发光效率、降低光学限制层的光学吸收损耗、改进p型掺杂层的电阻特性，提高了激光器的斜率效率和输出功率。研制出大功率连续激射的GaN基近紫外激光器，激射中心波长为393.6nm，阈值电流密度为2.4kA/cm2，在室温连续激射模式下，紫外激光器的输出功率高达381mW。我们还研制出脉冲大功率激射的GaN基近紫外激光器，脉冲功率高达20W，超额完成本课题“脉冲峰值功率达到5W”的研究目标。