Reliability improvement of GaN-based devices by controlling defects and interfaces

研究的目的是通过控制缺陷和界面来提高GaN基器件的稳定性。我们研究了GaN和AlGaN中缺陷和杂质的电子态及其与各种器件退化现象的关系，如电流崩塌、栅漏电流、电击穿等。1)我们对Al_(0.26)Ga_(0.74N)表面的肖特基接触进行了深能级瞬变谱(DLTS)测量，探测到激活能为0.9 eV、密度大于1×10~(-16)cm~(-1)的深电子陷阱。2)我们利用CN_x/SiN_x双层膜发展了碳掺杂GaN的扩散过程。当我们使用化学计量比的Si3N4作为覆盖层时，富C的CN_x层被沉积在n-GaN上。二次离子质谱仪(SIMS)的结果表明，在1000℃下热处理2小时后，碳在浓度大于1×10~(18)cm~(-3)的n-GaN中扩散。3)我们研制了一种…更新的控制AlGaN表面电子态的表面工艺，该工艺包括在AlGaN表面沉积超薄的Al层，并在700℃下原位超高真空退火，导致氧施主从AlGaN表面吸杂到Al层中。4)通过对绝缘体-GaN界面进行高温或紫外光辅助的电容-电压测量，我们可以首先观察到GaN中间禁带附近界面态的响应。研究了AlGaN/GaN高迁移率晶体管(HEMTs)在高温下施加关态应力后的工作稳定性。未采用超薄铝基表面控制工艺的器件在施加应力后直流特性显著下降，这主要是由于漏极电导的增加。另一方面，在应力处理后，HEMTs的直流特性没有随表面过程的变化而改变。较少

The purpose of the research is to improve the stability of the GaN-based devices by controlling defects and interfaces. We have characterized electronic states of defects and impurities in GaN and A1GaN, as well as their correlation with degradation phenomena in various kinds of devices, such as the current collapse, the gate leakage current, electric breakdown, etc.1)We performed deep level transient spectroscopy (DLTS) measurements on the Schottky contacts fabricated on the Al_0.26Ga_0.74N surfaces, and detected a deep electron trap with an activation energy of 0.9 eV and a density higher than 1 x 10^16 cm^<-3>.2)We developed a diffusion process for carbon doping into GaN, using a CN_x/SiN_x bilayer. The C-rich CN_x layer was deposited on n-GaN while we used stoichiometric Si3N4 as a capping layer. The secondary ion mass spectroscopy (SIMS) result indicated the C diffusion into n-GaN in concentration higher than 1x 1018 cm-3 after an annealing at 1000 ℃ for 2hrs.3)We have developed a … More novel surface process for controlling electronic states at the AlGaN surfaces, The process consists of the deposition of ultrathin Al layer on the A1GaN surfaces and the in-situ UHV anneal at 700 ℃, resulting in the gettering of oxygen donors from the A1GaN surface into the Al layer. After the process, we observed pronounced reduction of the leakage current and the temperature-dependent current-voltage characteristics in the Ni/AlGaN interfaces.4)By applying the high-temperature or UV-assisted capacitance-voltage measurements on the insulator-GaN interfaces, we could firstly observed the response from the interface states near midgap of GaN. We also found that the ultrathin Al-oxide layer on the GaN surface was very effective in controlling interface states.5)We investigated the operation stability of the A1GaN/GaN high-mobility transistors (HEMTs) after applying the off-state stress at high temperatures. The devices without the unltrathin-Al based surface control process showed significant degradation in DC characteristics after the stress, mainly due to the increase in the drain conductance. On the other hand, no change in the the DC characteristics were observed in HEMTs with the surface process after the stress. Less