Enhancement-Mode GaN-Based High-Electron Mobility Transistors on the Si Substrate With a P-Type GaN Cap Layer

摘要

An enhancement-mode (E-mode) high-electron mobility transistor (HEMT) was demonstrated by inserting a p-type GaN layer underneath the gate electrode. The effects of process flows and device structures on the electrical properties are investigated in this paper. We demonstrated a threshold voltage $(V_{rm{th}})$ of 4.3 V by adjusting the built-in voltage of the diode formed between the p-GaN and channel by the alloy temperature. Next, we found the existence of parallel conduction paths of the p-GaN layer and 2-D electron gas (2DEG) channel in such a HEMT structure. By removing p-GaN above the gate–source and gate–drain regions, current conduction migrates from p-GaN to 2DEG channel. The process window of the p-GaN residual thickness to ensure a steady forward current–voltage operation was estimated to be $10pm 5~{rm nm}$ in our case. Finally, with the p-GaN underneath the gate contact to deplete surface leakage current, an E-mode HEMT with a breakdown voltage $(V_{rm{BD}})$ of 1630 V is achieved.