AlGaN基垂直结构谐振腔紫外LED研究

Ultraviolet LEDs have important application values in the fields of curing, therapy, sterilization, short-distance communication, etc. AlGaN is a direct bandgap semiconductor material, and its emission wavelength is in the range of 200-365 nm. Thus, it is quite suitable for the fabrication of ultraviolet LEDs. At present, the luminous efficiency of AlGaN based ultraviolet LED is still very low. Main reasons are as follows: (1) The dislocation density of AlGaN is high, resulting in a low internal quantum efficiency of the device; (2) Light emission of high Al-content device is anisotropic, leading to a low light extraction efficiency; (3) The polarization effect in multiple quantum wells can induce a strong polarization electric field, giving rise to a low carrier radiative recombination efficiency. To overcome these difficulties mentioned above, we propose to develop AlGaN based vertical conducting resonant-cavity ultraviolet LED with tunneling junction on SiC substrate. SiC substrate is adopted to improve the quality of AlGaN epitaxy layer due to a better lattice matching between SiC and AlGaN, thereby enhancing the internal quantum efficiency of the device; The resonant-cavity structure formed by DBR is used to enhance the light-extraction efficiency of the device; The p-n junction reversed structure realized by a tunneling junction is proposed to weaken the polarization electric field and improve the carriers recombination efficiency in multiple quantum wells. Meanwhile, the vertical structure LED fabricated on the conductive SiC substrate can effectively avoid current crowding. This project is to obtain high performance AlGaN based ultraviolet LED, laying the theoretical and experimental bases of high-efficiency semiconductor ultraviolet light-emitting devices.

紫外LED在固化、医疗、杀菌、短距离通信等领域有重要应用价值。AlGaN为直接带隙半导体，发光波长从200nm到365nm，适合制备紫外LED。但是，目前的AlGaN基紫外LED发光效率较低，主要原因在于：（1）AlGaN材料位错密度高，导致器件内量子效率低；（2）高Al组分器件发光各向异性，致使光提取效率低；（3）量子阱极化效应引起强极化电场，使得载流子复合发光效率降低。为解决上述问题，我们提出在SiC衬底上研制带有隧道结的AlGaN基垂直结构谐振腔紫外LED。器件采用与AlGaN晶格更匹配的SiC衬底，改善AlGaN质量，提高内量子效率；利用DBR形成谐振腔，提高光提取效率；通过隧道结实现pn结倒置，减弱极化电场影响，提高量子阱内载流子复合发光效率。同时，垂直结构LED可有效避免电流拥堵效应。本项目将获得性能良好的AlGaN基紫外LED，为高效半导体紫外发光器件研究奠定理论与实验基础。

紫外LED在固化、医疗、杀菌、短距离通信等领域有重要应用价值。AlGaN作为直接带隙半导体适合制备紫外LED。但是，目前的AlGaN基深外LED发光效率较低。主要原因在于：（1）低位错密度的AlGaN材料制备较难，导致器件内量子效率低；（2）高Al组分器件发光各向异性，致使光提取效率低；（3）量子阱极化效应产生强内电场，引起载流子复合发光效率降低。为解决上述问题，本项目在SiC衬底上开展了AlGaN基谐振腔紫外LED研究。主要研究内容包括：SiC衬底AlGaN基薄膜材料的外延生长、掺杂、LED器件模拟仿真和制备等。通过本项目研究，实现了SiC衬底无裂纹高Al组分Al0.45Ga0.55N薄膜和AlGaN基多量子阱的外延生长；制备出高反射率AlGaN基DBR（峰值反射率达97%）；制备出宽阻带（25 nm）和高反射率（80%）复式AlGaN基DBR；实现了高空穴浓度（9×1017 cm-3）AlGaN薄膜极化诱导p型掺杂；研制出AlGaN基垂直结构隧道结紫外LED；研制出谐振腔紫外LED原型器件。本项目为具有自主知识产权的高效半导体紫外LED的产业化发展奠定了理论和实验基础。