Due to their superior breakdown fields compared with GaN and SiC and high thermal conductivity, Al x Ga 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 ultrawide‐bandgap (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 2 O 3 , and ZrO 2 is reported. As compared with similar geometry HFETs, these devices exhibit a simultaneous reduction in gate‐leakage 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 °C, whereas the peak drain currents decrease from ≈0.5 to 0.3 A mm −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 °C, the devices withstand repeated temperature cycles without catastrophic degradation or breakdown, underscoring the promise of these materials.
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Mollah et al. (2020) studied this question.