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 Al<sub>2</sub>O<sub>3</sub> gate dielectric have been investigated. Owing to the optimized AIN/GaN interface, very high carrier mobility (~1400 cm<sup>2</sup>/V ldr s) and high 2-D electron-gas density (~2.7times10<sup>13</sup>/cm<sup>2</sup>) 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<sub>m,ext</sub>~480 mS/mm (corresponding to g<sub>m,int</sub>~1 S/mm). An f<sub>T</sub>/f<sub>max</sub> of 52/60 GHz was measured on 0.25times60 mum<sup>2</sup> 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.

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