AlN/GaN Insulated-Gate HEMTs With 2.3 A/mm Output Current and 480 mS/mm Transconductance

High-electron mobility transistors (HEMTs) based on ultrathin AIN/GaN heterostructures with a 3.5-nm AlN barrier and a 3-nm Al₂O₃ gate dielectric have been investigated. Owing to the optimized AIN/GaN interface, very high carrier mobility (~1400 cm²/V ldr s) and high 2-D electron-gas density (~2.7times10¹³/cm²) resulted in a record low sheet resistance (~165 Omega/sq). The resultant HEMTs showed a maximum dc output current density of ~2.3 A/mm and a peak extrinsic transconductance g_m,ext~480 mS/mm (corresponding to g_m,int~1 S/mm). An f_T/f_max of 52/60 GHz was measured on 0.25times60 mum² gate HEMTs. With further improvements of the ohmic contacts, the gate dielectric, and the lowering of the buffer leakage, the presented results suggest that, by using AIN/GaN heterojunctions, it may be possible to push the performance of nitride HEMTs to current, power, and speed levels that are currently unachievable in AlGaN/GaN technology.