Generalised model for GaAs MESFET photodetectors

The gallium-arsenide MESFET as a ps light-pulse detector has created an environment whereby it is now possible to interface optical fibres and high-speed GaAs analogue-digital circuitry in optical communication links. High switching speed and low operating voltage, together with the optoisolation characteristics of GaAs MESFETs, have resulted in considerable research into uncovering some of the principles that govern the optical characteristics of the GaAs D-MESFET as a photodetector. During the last few years various mechanisms for the photoresponse of MESFETs have been proposed. However, there remains considerable controversy with regard to the mode of operation of the MESFET as an optical detector. In this paper an effort is made to explain the various experimental conditions that resulted in the different conclusions, and subsequently a more complete model is proposed which describes the various modes of operation and provides the basis for comparison between the various proposals.