Gallium arsenide photo-MESFET's

Photodetection response measurements performed on normally off GaAs photo-MESFETs are discussed. Two modes were investigated: (i) the normal mode in which the photon energy is greater than the bandgap and the light intensity is sufficient to bias the device above turn-on-threshold, and (ii) the subthreshold mode with subband-gap photon energy illumination. In the second mode, the transistor operates by internal photoemission from the metal gate to the semiconductor. In the normal mode, the square root of the drain photocurrent varies as the logarithm of the incident light intensity. The device characteristics for subband-gap illumination have been analyzed, and it is shown that the photocurrent varies linearly with light intensity in this mode.<
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