Published online by Cambridge University Press: 10 February 2011
Current collapse in GaN MESFETS is believed to result from the trapping of carriers in the high resistivity GaN layer, and can be reversed by the application of light. Light photoionizes (or photoneutralizes) the carriers, releasing them from the traps and restoring all or part of the original I-V characteristics of the device. In these investigations we have taken advantage of this effect to characterize the traps responsible for current collapse in an n-channel GaN MESFET. At fixed source-drain voltage, the incremental light-induced drain current, above that measured in the dark, and normalized per incident photon, is measured as a function of wavelength. The resulting photoionization spectrum reflects two absorption thresholds corresponding to two distinct electron traps. Because of the nature of the measurement, these traps can be identified as those responsible for current collapse in the device.