Degradation mechanism of Schottky P-GaN gate stack in GaN power devices under neutron irradiation

In this Letter, the degradation mechanism of Schottky p-type GaN (P-GaN) gate stack in GaN power devices under neutron irradiation is studied. After 1-MeV neutron irradiation at fluences of 6 × 1013 and 1 × 1014 neutron/cm2, device threshold voltage VTH is positively shifted and gate leakage current is increased, which indicates the degradation of Schottky P-GaN gate stack. By analyzing the gate current with Frenkel–Poole emission model, barrier height of Schottky P-GaN gate stack is reduced due to the traps induced by neutron irradiation. By employing capacitance–voltage (C–V) and pulse current–voltage (I–V) measurements, we find that the electron and hole traps induced by displacement damages dominate the degradation of gate characteristics after neutron irradiation. Electron traps at EC- (0.38–0.55) eV and hole traps at EV+ (0.56–0.62) eV with a density of 1011–1012 cm−2 eV−1 are shown in irradiated devices. Ionizations of VGa and Gai induced by neutron radiation as well as their interaction with dislocations significantly alter the energy band of P-GaN/AlGaN/GaN heterostructure gate stack. The trapping and de-trapping processes of VGa-related electron traps lead to positive shifts in VTH. Passivation of dislocations by Gai effectively lowers the barrier height for holes and increases the gate leakage current. Measures to improve the quality of P-GaN/AlGaN/GaN heterostructure or raise the potential barrier height can be taken to make the device more resistant to neutron radiation. This work depicts the physical process and mechanism of degradations in Schottky P-GaN gate stack, which can provide deeper insights into the analysis and field application of GaN power devices under neutron irradiation.