Structural optimization and analysis of GaAs buried-gate OPFET for visible-light communication

Abstract

Opto-Electronic Integrated Circuit (OEIC) receivers offer greater advantages over other discrete devices in Visible Light Communication (VLC). Use of Optical Field-Effect Transistor (OPFET) as a photodetector-cum-amplifier has been amply identified for VLC and other related applications. OPFET offers simultaneous high sensitivity, large bandwidth, and high unity-gain cut-off frequency in relation to other state-of-art p-i-n and avalanche photodiodes (APDs). OPFET also has the additional advantage of the ability to operate at lower voltages than photodiodes. In this paper, we carry out the structural optimization of medium- and long-channel GaAs buried-gate OPFET for 600 nm wavelength operation with an in-depth analysis based on the photoconductive and photovoltaic effects, the scaling rules-induced effects, and the channel length variation effects. The bandwidth and the unity-gain cut-off frequency (fT) are simultaneously optimized with a responsivity greater than 2 × 105 A/W as a constraint. The optimization with and without any constraint on the dark current is discussed. Simulation results demonstrate that it is possible to achieve simultaneous detection and amplification up to modulation frequencies of 1.9 GHz and 3.6 GHz at radiation flux densities of 1016 and 1019 /m2-s. Corresponding responsivities of 108 and 106 A/W or higher are also achievable surpassing what is achievable in photodiodes. Simulation results are in line with previously published experimental results. The study results hold out the promise of a better potential use of OPFET for high data rate VLC applications. Remarkably, the manuscript establishes and explains for the first time the direct relationship of the 3-dB bandwidth with gate length.