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Effects of Electrode Spacing on the Response of Optically Controlled MESFETs

Summary: WP1
Effects of Electrode Spacing on the Response of Optically
Controlled MESFETs
M. A. Alsunaidi and M. A. Al-Absi
King Fahd Universityof Petroleum and Minerals,Dhahran 31261, Saudi Arabia
Email: msunaidi@kfupm.edu.sa
In microwave GaAs MESFETs, camer transport is a strong function of carrier energy.When
illuminated, the carrier energy and carrier distribution inside the device are substantially
affected by the incident optical energy. To account for these effects an accurate model based
on the energy formulationof the transport equation coupled with optical energy conversion
equations is used [1-21, This model is used to investigate the optimum design of optically
controlled MESFET structures consideringthe trade-off between the degradationin electric
characteristics and the improvement in photoelectric conversion efficiency. Time domain
simulations show the significant effect of electrode spacing, specifically, the drain-gate
separation (Fig. 1). Interesting observations are made when the drain-gate separation was
varied from 0.3to 1.4 p.Devices with different drain-gate spacing responddifferently to a
futed-waist Gaussian light pulse in terms of peak output photocurrent, waveformrise time
and waveform fall time. The peak value of the output photocurrent increases sharply, as
more device area is exposed to light, but starts to level up after a certain value of dram-gate
spacing where no appreciable gain is observed (Fig. 2a). This behavior is due to the


Source: Al-Absi, Munir A. - Electrical Engineering Department, King Fahd University of Petroleum and Minerals


Collections: Engineering