High-Temperature Operation of Al_xGa_(1-x)N (x >0.4) Channel Metal Oxide Semiconductor Heterostructure Field Effect Transistors with High-k Atomic Layer Deposited Gate Oxides

摘要

Due to their superior breakdown fields compared with GaN and SiC and high thermal conductivity, Al_xGa_(1-x)N (x >0.4) channel high-electron-mobility transistors (HEMTs) will find applications in extreme environments such as power electronics. Herein, the high-temperature operation of ultrawidebandgap (UWBG) Al_(0.65)Ga_(0.35)N/Al_(0.4)Ga_(0.6)N metal oxide semiconductor heterostructure field effect transistors (MOSHFETs) with atomic layer-deposited (ALD) high-k gate dielectrics TiO_2, Al_2O_3, and ZrO_2 is reported. As compared with similar geometry HFETs, these devices exhibit a simultaneous reduction in gateleakage current by ≈10~4 and a positive shift of the threshold voltage as much as 4 V. This positive threshold shift indicates the introduction of negative charges at the oxide/barrier interface and within the thin oxide, attributed to the pre-ALD plasma treatment. The gate leakage increases weakly with temperature up to 250 ℃, whereas the peak drain currents decrease from ≈0.5 to 0.3 Amm~(-1). An analysis of the C–V and Ⅰ–Ⅴ characteristics reveals that this drain current decrease is due to a reduction in channel electron mobility. The potential mechanisms responsible for this are discussed. Up to the measured temperature of 250 ℃, the devices withstand repeated temperature cycles without catastrophic degradation or breakdown, underscoring the promise of these materials.