Effect of traps on low-temperature high electron mobility transistor characteristics

The I-V characteristics of MBE-grown AlGaAs/GaAs high electron mobility transistors (HEMT's) are studied using a bias and temperature sequence between 77 and 300 K to control trap occupancy. Low-temperature threshold voltage, transconductance, and saturation current are found to be either increased or decreased significantly relative to their 300 K values depending on the gate bias condition during cool down. This behavior is shown to be caused by variations in trap occupancy in the highly doped AlGaAs layer.