Optical gain and large-signal characteristics of illuminated GaAs MESFET´s

The illuminated large-signal characteristics of a uniformly doped epitaxial GaAs MESFET have been measured when optically gated with an He-Ne laser source. The dependence of the measured optical gains on the applied electrical biases and optical intensity, position, and spot size indicate that the dominant dc gain mechanisms are transit time photoconductivity combined with an effective photovoltaic change in the pinchoff voltage. The photovoltaic change in the pinchoff voltage dominates for high optical power levels, while the photoconductive response dominates for low power levels. Optical gains in the range of 5-10 were measured for the photoconductive regime, while gains in the range of 50-70 were measured for the photovoltaic regime.