CHARGE COLLECTION IN GAAS-MESFETS AND MODFETS

A comparison of the amount of charge collected at the drains of GaAs MESFETs irradiated with pulsed laser light and ions and having different gate lengths shows orders of magnitude more charge collected for 0.1-mu-m MESFETs than for 1.2-mu-m MESFETs manufactured using different processes. Analyses of the dependence of the photocurrent pulses on gate and drain voltages, temperature, and light intensity suggest that the enhanced charge collection is primarily due to modulation of the channel width by positive charge trapped in the vicinity of the channel. Enhanced charge collection via channel modulation also occurs in pseudomorphic MODFETs. Pulses with characteristics similar to those produced by laser light, i.e., large amplitudes and long decay times, were obtained when 0.1-mu-m MESFETs were irradiated with He and Si ions. These results reveal the important role played by traps in determining SEU sensitivity in GaAs MESFETs with short gate lengths.