AlN/AlGaN heterojunction field-effect transistors with a high-AlN-mole-fraction Al_0.72Ga_0.28N channel grown on single-crystal AlN substrate by metalorganic chemical vapor deposition

Abstract

This paper presents research results on AlN/AlGaN heterojunction field-effect transistors (HFETs) with a high-AlN-mole-fraction Al0.72Ga0.28N channel grown on a single-crystal AlN substrate by metalorganic chemical vapor deposition. Material evaluation results confirmed that the grown AlGaN layer was 100% coherently strained for the underlying AlN substrate and thereby had superior crystal quality as well as the substrate. The fabricated AlGaN-channel HFETs with a gate length of 2 μm exhibited pinch-off characteristics with the max. current density (IDS_MAX) of 21 mA/mm, the on-state resistance of 250 Ωmm, the peak transconductance of 4.5 mS/mm with the threshold voltage of –4.6 V, and the on/off ratio of 4 × 105. The temperature dependence of DC characteristics confirmed that the IDS_MAX decreased by 15% and the off-leakage current increased from 60 nA/mm to 10μA/mm within the temperature range from the room temperature to 200℃.