Temperature-Dependent Hot Electron Effects and Degradation Mechanisms in 650-V GaN-Based MIS-HEMT Power Devices Under Hard Switching Operations

This article proposed a hard switching high-temperature reverse bias (HS-HTRB) stress test method with a high measurement delay tolerance to study the impacts and mechanisms of hot electron effects on the stability of threshold voltage (
$V_{\mathrm {th}}$
) in 650-V gallium nitride (GaN)-based metal–insulator–semiconductor high-election mobility transistors (MIS-HEMTs). Conventional HTRB and high-temperature constant source current (HTSC) stress tests have been carried out as well. The electric field caused emission (or detrapping) of electrons in dielectrics results in a negative
$V_{\mathrm {th}}$
shift, while buffer electron trapping leads to a positive
$V_{\mathrm {th}}$
shift and degrades subthreshold slope. The hot current affects
$V_{\mathrm {th}}$
in two different ways: channel impact ionization generates and accumulates holes under the gate and, thus, shifts
$V_{\mathrm {th}}$
negatively by lowering the gate–source barrier, while injected hot electrons themselves shift
$V_{\mathrm {th}}$
positively by depleting the channel electrons. As temperature rises, the intensity of impact ionization decreases while the hot electron injection strengthens. The appropriate level of hot current and substrate termination can help compensate the field-induced negative
$V_{\mathrm {th}}$
shifts, ensuring a more stable working
$V_{\mathrm {th}}$
and, thus, a more reliable device for HS operations.