Slow Detrapping Transients due to Gate and Drain Bias Stress in High Breakdown Voltage AlGaN/GaN HEMTs

摘要

Charge trapping and slow (from 10 s to $>$ 1000 s) detrapping in AlGaN/GaN high electron mobility transistors (HEMTs) designed for high breakdown voltages ( $>$ 1500 V) is studied through a combination of electrical, thermal, and optical methods to identify the impact of Al molefraction and passivation on trapping. Trapping due to 5–10 V drain bias stress in the on-state $(V_{gs} = hbox{0})$ is found to have significantly slower recovery, compared with trapping in the off-state $(V_{gs} < V_{rm th}, V_{ds} = hbox{0})$. Two different trapping components, i.e., TG1 $(E_{a} = hbox{0.6} hbox{eV})$ and TG2 (with negligible temperature dependence), in AlGaN dominate under gate bias stress in the off-state. $hbox{Al}_{0.15} hbox{Ga}_{0.85}hbox{N}$ shows much more vulnerability to trapping under gate stress in the absence of passivation than does AlGaN with a higher Al mole fraction. Under large drain bias, trapping is dominated by a much deeper trap TD. Detrapping under monochromatic light shows TD to have $E_{a} approx hbox{1.65} hbox{eV}$. Carbon doping in the buffer is shown to introduce threshold voltage shifts, unlike any of the other traps.