AlGaN日盲紫外雪崩探测器的漏电机理及器件研制

The fabrication of low leakage current high multiplication gain AlGaN-based solar-blind avalanche photodetectors(APDs) is very significant for development of UV detection in military and civilian applications. This proposal is initiated by fabricating high multiplication gain AlGaN-based solar-blind APDs, leakage current mechanisms of AlGaN solar-blind APDs are carefully studied and analyzed in order to identify the cause and path of leakage current, then the relevant MOCVD process and detectors process techniques are investigated to reduce the leakage currents of AlGaN detectors according to different leakage locations. Low dark current high multiplication gain AlGaN-based solar-blind APDs will be successfully fabricated. Back-illuminated separate absorption and multiplication (SAM) type AlGaN APDs with separate absorption and multiplication structure are grown by metal organic chemical vapor deposition on double-side polished sapphire substrates. In order to efficiently control devices leakage current and local breakdown, the influences of AlGaN-based materials crystal quality, doping method, devices etching and passivation process etc. on device leakage current are analyzed systemically. On the basis of solving the the parasitic reaction of Al, surface morphologies and dislocation density control, uniform and effective p-type doping, the higher quality AlGaN epitaxial materials for meeting the design requirements solar blind AlGaN APDs are grown by MOCVD. Then the ohmic contact formation, etching and damages control, prevent oxidation, sidewall passivation, the electric field uniformity control on the AlGaN material are investigated. The devices performance is evaluated by measurements of dark current and spectral response characteristics etc.. and the results is feedbacked to the structure design, material growth and process. Low leakage current high multiplication gain AlGaN APDs with cutoff wavelength is less than 280nm are fabricated finally.

研制低漏电高增益AlGaN日盲雪崩探测器在军事和民用紫外探测方面有着非常重要的意义。本项目从研制低漏电流高增益AlGaN日盲APD出发,深入研究AlGaN基APD的反向偏置漏电流的机理,识别漏电流的起源,根据不同的漏电起源,研究采取相应的MOCVD外延和器件工艺技术,减小漏电流。通过MOCVD生长吸收层和倍增层分离的背照射AlGaN日盲APD材料,为有效控制器件漏电和局域击穿,探究AlGaN的晶体质量、掺杂方法和器件刻蚀、钝化等对漏电流的影响。在解决好Al原子寄生反应、表面形貌和位错密度控制、均匀有效P型掺杂的基础上生长出高质量的AlGaN 日盲APD外延材料。在外延材料结构上开展欧姆接触、刻蚀及损伤控制、防止氧化及侧面钝化、电场均匀性控制等工艺研究。采用暗电流特性及光谱响应等测试方法对探测器的性能进行评估,并将结果反馈到材料和工艺中,研制出截止波长≤280nm的高增益AlGaN APD。

研制低漏电高增益AlGaN日盲雪崩探测器在军事和民用紫外探测方面有着非常重要的意义。我们在常规的两步法外延基础上，采用我们提出的“复合缓冲层”的方法，极大减小了AlN生长初期的衬底氮化的影响，从而采用常规的MOCVD设备在1100℃左右也生长出了高质量的AlN材料，并大幅度地降低了刃位错密度，突破了AlN材料的外延生长技术。通过生长AlN/AlGaN超晶格层做为插入层，有效过滤位错，提高AlGaN材料质量。生长出了较高质量的AlGaN材料，其（002）面XRD半高宽仅为180秒左右。建立了观察GaN基探测器在反向偏压下光致发光情况和在高反向偏压下电离发光的观测系统，可以观察GaN基探测器高压下漏电来源位置。通过不同尺寸的探测器制备和测量分析，确定了GaN基探测器漏电来源，针对外延缺陷导致的漏电来源，我们调整蓝宝石衬底上生长GaN的方法，控制三维生长的时间，抑制了大尺寸器件漏电。设计了AlGaN日盲雪崩探测器制作工艺和相应的光刻版图并进行了工艺实施。制备出高增益GaN材料雪崩探测器，倍增系数达到了5×104；制备出响应截止波长在280nm左右的日盲AlGaN材料pin结构探测器，在背照射方式下的响应度峰值在波长270nm左右达到0.190 A/W。制备出了日盲AlGaN材料SAM结构APD探测器，实现了增益1.3×104。