高亮度、低垂直发散角GaSb基布拉格反射波导半导体激光器研究

High power GaSb-based diode lasers in the mid-infrared wavelength range are of great importance for many applications such as gas detection, optic-electronic countermeasure, plastic welding, as well as medical diagnostics. However, conventional GaSb-based diode lasers suffer from very large vertical divergence angle (>60 degree) and low brightness, limiting the direct applications. In order to overcome this problem, this project will introduce Bragg reflection waveguide (BRW) into the vertical heterojunction structure of GaSb-based diode laser, which utilizes the photonic bandgap effect rather than traditional total internal reflection to confine light. The BRW laser can be designed to have large mode volumes while maintaining stable single mode operation, resulting in ultra-low vertical divergence angle. In this project, high strained InGaAsSb quantum well and high bandgap energy AlGaAsSb barrier layers in the active region are used to ensure strong hole carrier confinement and high internal quantum efficiency. Moreover, the BRW lasers can achieve low series resistance by the 3-layer grading and modulated doping in waveguide design. With an asymmetric period of p- and n-doped BRWs, the reduced p-side thickness results in a low thermal resistance and internal losses. To furtherly improve the brightness, the tapered gain region structure is employed in the lateral direction of GaSb-based diode laser to produce both high output power and a good beam quality simultaneously. As a result of the novel laser design, high quality epitaxial growth and device fabrication, the 2.3μm diode lasers are expected to output high brightness (0.4W in CW and 1W in pulse, vertical divergence angle<15 degree) mid-infrared laser.

高功率GaSb基中红外半导体激光器在气体检测、光电对抗、塑料焊接及医疗等领域具有广阔的应用前景，但传统器件面临垂直发散角高达60度以上、亮度低的问题，严重限制了其应用发展。为解决这一难题，本项目提出在GaSb基半导体激光器的垂直方向采用布拉格反射波导结构，利用光子带隙效应取代传统的全反射进行光场限制，获得大模式体积、稳定单模工作，从而有效降低垂直发散角。同时，本项目还采用以下新结构：有源区采用高应变InGaAsSb量子阱和高带隙AlGaAsSb势垒材料，增强空穴限制，提高内量子效率；异质结界面采用3层组分渐变、调制掺杂技术降低势垒获得小的串联电阻；减小p型布拉格反射波导的厚度，降低器件的热阻和内部损耗；侧向采用锥形结构，提高输出功率和光束质量。通过上述材料结构设计、高质量外延生长和器件制备，在2.3μm波长实现高亮度(连续>0.4W，脉冲>1W，垂直发散角<15度)的激光输出。

高功率半导体激光器在泵浦、材料加工、医疗、传感、空间通讯和国防上有着极其重要的应用，但传统边发射半导体激光器面临垂直发散角大、椭圆光斑、光束质量差等瓶颈性难题，严重制约了其直接应用。为解决该难题，本项目研究布拉格反射波导在锑化物半导体激光器中的应用，它利用光子带隙效应限制光场来实现大光模式尺寸稳定单横模工作，同时本项目还研究了新的侧向模式调控结构，在保持高功率输出的改善垂直和侧向发散角，从芯片层次改善光束质量，实现高亮度激光输出。本项目主要研究成果如下：.(1) 研制出808nm波段高功率、极低发散角、圆形光束布拉格反射波导半导体激光器，90 μm条宽单管连续功率4.6 W，垂直发散角半高全宽4.9°，含95%功率垂直发散角低至9.8°，激光器保持稳定的圆形光束输出，其直接光纤耦合效率可达90%以上。.(2) 研制出锥形布拉格反射波导半导体激光器，单管连续功率超过1W，垂直发散角低至7.2°，水平发散角低至1.3°，近衍射极限输出，亮度超过80 MW.cm-2.sr-1。.(3) 采用鱼骨形微光学结构，制备的2 μm波段锑化物宽区半导体激光器连续功率提高至1.1 W，侧向发散角相对宽区激光器降低约57%。.(4) 制备了高效率微条耦合锑化物中红外半导体激光器，最高连续功率达到1.27 W，特征温度和光谱特性明显改善，相对普通的宽区激光器侧向发散角降低约30%。.(5) 采用多种注入电流调控结构（棋盘式周期性调制、侧向脊波导宽区结构、梯形台面结构），实现了远场近无注入电流依赖，同时器件输出功率也得到提高。.(6) 发表论文12篇（SCI论文10篇），会议论文4篇，申请专利8项，授权专利2项，培养研究生3名。. 该研究成果有利于简化半导体激光应用光学系统及降低成本，推动下一代高亮度半导体激光光源的研发。