Temperature-Dependent Dynamic Degradation of Carbon-Doped GaN HEMTs

Temperature-dependent dynamic degradation was investigated for C-doped GaN high electron mobility transistor (HEMT) from 300 to 20 K. Pulsed I- V measurements with various OFF-state quiescent bias voltages revealed that current collapse (C.C.) induced by charge-trapping effect at room temperature was greatly suppressed and monotonously declined as decreasing temperatures. This was attributed to reduced number of electrons which were injected into the C-doped layer and capable of overcoming capture potential barrier. Drain current transient measurements were employed to investigate temperature-dependent and time-resolved carrier capture/emission process. Based on the extracted time constants, an activation energy of 0.36 eV was identified for the electron capture process. For carrier emission process, both current-based and capacitance-based transient analysis indicated an activation energy around 0.20 eV. Furthermore, the traps were confirmed to be located in the C-doped layer by varying the pulse stimulus in deep-level transient spectroscope (DLTS). The measurement results showed that C-doped HEMTs grown on Si substrates exhibited high-saturation current, stabilized threshold voltage, and minor C.C. at cryogenic temperatures, particularly in comparison with those at room temperature.