PHOTOELECTRIC-EMISSION AND CONDUCTANCE STUDIES ON FULLY FABRICATED PHEMTS

Photoelectric measurement techniques are ideally suited to investigate barrier and bandgap energies in pseudomorphic heterostructure FETs. I n these devices the bandgap in the channel is smaller than that of the substrate and hence there exists a wavelength window in which the sub strate is transparent and the channel is absorbing. Consequently, phot oelectric measurements can be performed on fully fabricated PHEMTs usi ng backside illumination. In this paper we describe photocurrent measu rements for two distinct processes: photoemission of carriers between the Schottky gate and the channel, and photoconduction through the cha nnel. We have successfully modeled the observed shift in the onset of photoconduction using a self-consistent Schrodinger-Poisson solution. The peak photocurrent magnitude shows non-monotonic dependence on gate bias, possibly suggesting amplification of the photocurrent.