Comparison of various gate dielectrics on the performance of AlGaN/GaN HFETs

摘要

We report a comparison of various gate dielectrics including SiO_2, Si_3N_4, ZrO_2 and Pb(Zr, Ti)O_3 (PZT) on AlGaN/GaN heterojunction field-effect transistors, deposited by PECVD, MBE, and sputtering respectively. In terms of I-V characteristics, maximum drain-source current could be enhanced under positive gate voltage and the reverse leakage current level decreases by orders of magnitude. In terms of DC measurements, very thin SiO_2 layers can improve performance, which may be due to the passivation effect to remove surface states. No significant difference exists between control and the Si_3N_4 and ZrO_2 samples. Slightly reduction in transconduction is observed on the sample with PZT probably because of the much thicker layer was utilized. The thickness of insulator layers examined from C-V measurements reveals a better crystal quality can be obtained by PECVD deposition. While the RF S-parameters measurements shows the PZT gate dielectric brings the highest cut-off frequency or the lowest gate capacitance confirmed also by C-V data, which makes it a better candidate for microwave applications.