Extreme Temperature Operation of Ultra-Wide Bandgap AlGaN High Electron Mobility Transistors

High Aluminum content channel (Al
_0.85
Ga
_0.15
N/Al
_0.7
Ga
_0.3
N) High Electron Mobility Transistors (HEMTs) were operated from room temperature to 500°C in ambient. The devices exhibited only moderate reduction, 58%, in on-state forward current. Gate lag measurements at 100 kHz and 10% duty only showed a slight reduction in pulsed current from DC at 500°C and high gate voltages. Interfacial trap densities were 2 × 10
¹¹
over the range 25-300°C and 3 × 10
¹²
cm
^-2
from 300500°C from the subthreshold swing. These low interfacial trap densities and the near ideal gate lag measurement indicate high-quality epi layers. The insulating properties of the barrier layer led to low gate induced drain leakage current of ~ 10
^-12
A/mm and ~ 10
^-8
A/mm at 25 and 500°C, respectively. Low leakage current was enabled by the high Schottky barrier of the Ni/Au gate, 1.1 eV and 3.3 eV at 25 and 500°C, respectively. These properties of the AlGaN channel HEMTs demonstrate their potential for high power and high temperature operation.