Fabrication of super sensitive ultraviolet photodetector

为了制备高阻非掺杂GaN，生长条件与电学性能之间的关系已经被深入研究。研究发现，随着生长过程中氨气流量的增加，未掺杂GaN的电阻率越来越高。获得了杂质浓度小于10 μ cm ~ 3的高纯未掺杂GaN<14>，建立了新的生长顺序，使蓝宝石衬底上GaN的穿透位错密度降低了两个数量级以上。将该方法应用于AlGaN的生长，可以生长出无裂纹、高质量、成分范围广的AlGaN，并利用该方法生长的非掺杂GaN制作了紫外光电池。即使在功率为100 pW/cm ^2的极弱光照条件下，它也表现出光响应。制备了基于非掺杂Al_ Ga_ N的紫外光电池<0.2><0.8>。截止波长为335 nm，灵敏度为5A/W，是目前世界上最高的。漏电流的来源已被深入研究。在低偏置条件下，通过梅萨的表面漏电流占主导地位，而在高偏置条件下，隧道电流占主导地位。新型光电二极管显示出非常低的漏电流，仅为0.8pA。

In order to fabricate highly resistive undoped GaN, correlation between growth condition and electrical properties has been intensively studied. It is found that with increase of ammonia flow rate during growth, resistivity of undoped GaN become higher and higher. Highly pure undoped GaN with residual impurity concentration of less than 10^<14>cm^3 has been achieved.New growth sequence has been established, by which threading dislocation density of GaN on sapphire has been reduced more than two orders of magnitude. This new method was also applied to grow AlGaN.Crack free and high quality AlGaN with a whole compositional range can be grown.UV photo-cell was fabricated using undoped GaN grown by the new method. It showed photo-response even under the very weak illumination condition with a power of 100pW/cm^2. UV photo-cell based on undoped Al_<0.2>Ga_<0.8>N was also been fabricated. Cut off wavelength is 335 nm, and the sensitivity is 5A/W, which is the world's highest ever reported.GaN based pn-junction diode was fabricated. Origin of the leakage current has been intensively studied. At low bias condition, surface leakage current through mesa is dominant, while at high bias condition, tunnel current is dominant. The new photodiode showed very low leakage current of 0.8pA.