Photoionization spectroscopy of traps in GaN metal-semiconductor field-effect transistors

Measurements of the spectral and intensity dependences of the optically-ind uced reversal of current collapse in a GaN metal-semiconductor field-effect transistor (MESFET) have been compared to calculated results. The model as sumes a net transfer of charge from the conducting channel to trapping stat es in the high-resistivity region of the device. The reversal, a light-indu ced increase in the trap-limited drain current, results from the photoioniz ation of trapped carriers and their return to the channel under the influen ce of the built-in electric field associated with the trapped charge distri bution. For a MESFET in which two distinct trapping centers have been spect rally resolved, the experimentally measured dependence upon light intensity was fitted using this model. The two traps were found to have very differe nt photoionization cross-sections but comparable concentrations (4x10(11) c m(-2) and 6x10(11) cm(-2)), suggesting that both traps contribute comparabl y to the observed current collapse. [S0021-8979(00)00417-5].