AlGaN/GaN MISHEMTs with Sodium-Beta-Alumina as the Gate Dielectrics

AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) with sodium beta-alumina (SBA) thin films as the gate dielectrics are studied. AlGaN/GaN metal-semiconductor high-electron-mobility transistors (MESHEMTs) and MISHEMTs with Al₂O₃ thin-film gate dielectrics are also fabricated for comparative study. The MISHEMTs with SBA gate dielectrics show nearly four orders of magnitude lower gate leakage current and an approximately 60% increase in maximum transconductance, indicating that SBA can serve as an effective dielectric for AlGaN/GaN MISHEMTs. However, SBA gate dielectrics result in threshold voltage modulation of AlGaN/GaN MISHEMTs. Compared with those of AlGaN/GaN MESHEMTs, the threshold voltages of AlGaN/GaN MISHEMTs with Al₂O₃ gate dielectrics shift negatively from ?5.5 V to ?7.5 V. In contrast with the normally used gate dielectrics, the threshold voltages of MISHEMTs with SBA gate dielectrics shift positively from ?5.5 V to ?3.5 V. Based on an x-ray photoelectron spectrum study and energy band spectrum calculation, the primary mechanism of the threshold voltage modulation is attributed to the decrease in the surface valence-band maximum and the increase in the barrier height by SBA gate dielectrics.