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

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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