The influence of lightly doped p-GaN cap layer on p-GaN/AlGaN/GaN HEMT

Abstract

In this paper, the influence of a lightly doped p-GaN (p−-GaN) cap layer on p-GaN/AlGaN/GaN high electron mobility transistors (HEMTs) (LDP-HEMTs) was investigated. No difference in output or off-state breakdown characteristics was observed, but there was a negative shift in threshold voltage (V TH). The gate leakage (V GS = 7 V) dropped by three orders of magnitude, and the gate forward breakdown voltage and continuous operating voltage increased by 6.5 V and 2.5 V, respectively. It is worth noting that the gate characteristics are significantly optimized, which is ascribed to the employment of the p−-GaN cap layer. The simulations illustrate that the electric field is dispersed, and the electric peak is alleviated by the p−-GaN cap layer, thus suppressing the impact ionization and carrier injection in the high electric field. Furthermore, there is a negligible effect on the temperature reliability of V TH based on the temperature-dependent characteristics in LDP-HEMTs. However, the temperature stability of the gate current (V GS = 7 V) will worsen in LDP-HEMTs due to the difference in the conduction mechanism, compared with conventional p-GaN HEMTs.