Si衬底GaN基激光器的应力与缺陷调控研究

GaN-based laser diodes (LDs) have been widely used in the field of laser display and laser illumination. Now the price of free-standing GaN substrates is quite expensive, which makes the fabrication cost of GaN-based LDs quite high. By using Si substrates, the cost could be reduced by 2-3 orders. However, a high density of defects and crack network exists in GaN-on-Si LDs due to large mismatch in lattice constant and thermal expansion between GaN and Si, which affects the performance and lifetime of GaN-on-Si LDs seriously. This proposal will focus on stress regulation and defect control of GaN-on-Si blue LDs based on existing GaN-on-Si violet LDs, the mutual relationship between stress and defects will be also studied. This proposal will also propose a new LD structure based on epitaxial lateral overgrowth innovatively. The SiO2/SiNx dielectric mask with composite structure not only can reduce the threading dislocations by 2-3 orders but replace traditional AlGaN cladding layer. Compared with conventional LDs, LDs with this structure have many advantages, such as less stress, lower defect density, better optical confinement and smaller resistance, which are expected to improve the performance and lifetime of GaN-on-Si blue LDs.

GaN基激光器在激光显示和激光照明等领域具有广阔的市场应用前景。目前自支撑GaN衬底价格昂贵，同质外延的激光器制造成本较高。采用Si衬底制作激光器，有望将成本降低2-3个数量级。但是由于GaN与Si衬底之间存在大的晶格失配、热膨胀系数失配和激光器AlGaN光场限制层应力，GaN基激光器中应力大、缺陷密度高，严重影响Si衬底激光器的性能和寿命。本项目拟在已有Si衬底紫光激光器研究基础上，围绕Si衬底蓝光激光器这一大失配、强极化体系中的应力调控和缺陷控制开展工作，研究应力与缺陷之间的相互作用。本项目创新提出了一种基于侧向外延技术的新型激光器结构，采用SiO2/SiNx反射性复合结构作为侧向外延的介质掩膜，不仅可降低穿透位错密度2-3个数量级，还可取代传统AlGaN光场限制层。该新型激光器中的应力小、缺陷密度低、光场限制好、串联电阻小，有望大幅提升Si衬底GaN基激光器的性能和寿命。

氮化镓(GaN)基激光器在激光显示、激光照明等领域具有广阔的市场应用前景。现有GaN基激光器均生长在尺寸小且价格昂贵的自支撑GaN衬底(2英寸衬底单价1万元)上，导致激光器的价格昂贵。采用硅衬底(6英寸衬底单价250元)制备GaN基激光器，有望大幅降低激光器的制造成本。此外硅衬底GaN基激光器还有望与硅基微电子实现片上集成，因此成为了国际GaN领域的研究热点之一。然而GaN与硅衬底之间存在巨大的晶格失配和热膨胀系数失配，导致硅衬底GaN基激光器中应力大、缺陷密度高，严重影响了激光器的器件性能和寿命。基于此，本项目围绕硅衬底GaN基激光器这一大失配、强极化体系中的应力调控和缺陷控制等关键科学问题开展研究工作，研究了采用Al组分渐变的AlN/AlGaN缓冲层对硅衬底GaN基激光器中的应力与缺陷进行调控，利用缓冲层建立的压应力，抵消生长结束后降温过程中因热膨胀系数失配而产生的张应力，抑制了裂纹的产生；同时压应力还可以促使位错拐弯，发生相互湮灭，进一步提高材料质量。另外本项目还研究了硅衬底GaN的侧向外延生长技术，将硅衬底GaN材料的位错密度降低了2个数量级。基于上述研究，本项目取得的主要研究成果如下：(1)生长了高质量的硅衬底GaN材料，材料质量处于国际前列；(2)研制了国际首支室温电注入激射的硅衬底GaN基蓝光(450 nm)、近紫外光(389 nm)激光器，相关成果分别发表在Light: Science & Applications和ACS Photonics期刊上；(3)实现了国际首支硅衬底GaN基微盘激光器的室温电注入激射，相关成果以第一作者或通讯作者发表在Photonics Research和Optics Express期刊上。上述相关成果得到了Semiconductor Today等国际半导体专业媒体的持续跟踪报道。在本项目资助下，共发表高质量学术论文14篇，其中第一作者或通讯作者论文10篇；共申请发明专利6项，培养研究生2名，本人共参加国内外学术会议并作硅衬底GaN激光器相关的口头报告8次。本项目完成了预期的研究目标。目前硅衬底GaN基激光器的阈值电流和阈值电压较高。我们拟通过设计新型的激光器结构等方法，来进一步提升激光器的器件性能和寿命。