High-performance normally-off recessed tri-gate GaN MIS-FETs in micrometer scale

In this study, a normally-off AlGaN/GaN metal-insulator-semiconductor field-effect transistor (MIS-FET) based on the combination of tri-gate and recessed MIS gate is fabricated and characterized. The recessed tri-gate MIS-FET is manufactured by micro-level trenches, defining the fin-shaped channel and improving the gate control capability. The recessed surface is cleaned by a diluted buffered oxide etch, HCl solution, and tetramethylammonium hydroxide treatment before a 20 nm Al2O3 deposition by atomic layer deposition. After deposition, post-deposition annealing was carried out. Recessed tri-gate MIS-FET demonstrates a high threshold voltage of 3.1 V, a high drain current of 1121 mA mm-1, and an on/off current ratio of 2 108. A smaller on-resistance of 5.4 Ω mm compared with recessed planar MIS-FET of 12.7 Ω mm is achieved. Besides, the devices show a low I-V hysteresis. All experimental results confirm micro-level trenches realize the advantages of the recessed tri-gate structures, which supports a promising technique to pursue the normally-off operation of GaN high electron mobility transistors.