Análise de transistores de efeito de campo para microondas controlados por feixe óptico

Abstract

Significant amounts have been invested in the research of photonic integrated circuits. Semiconductor materials, among which gallium arsenide (GaAs) as well as alloys based on it, such as aluminum gallium arsenide (GaAlAs), are used in the manufacturing process of those circuits. Gallium arsenide can be associated to a metallic electrode to make a Schottky junction, and it is used to form a Metal-Semiconductor Field-Effect- Transistor (GaAs MESFET). The behavior of such device under the incidence of a modulated optical beam is discussed in this paper. Computational analyses designed through the MATLAB® tool allow verification of the influence of the optical beam on the internal parameters of the device, such as the capacitance between drain and source and between gate and source; the distributed capacitance in the channel; the transconductance and other elements involved in its performance. Based on those, the expressions of the factors which make up the admittance matrix (Y) are calculated. From that matrix are obtained the equations for voltage gain and input impedance, which are important factors in photodetection. All of those elements are determined by the density of the beam’s optical power, which is modulated with high transmission rates. The analyses take into account the photovoltaic and photoconductive effects on the behavior of the GaAs MESFET. Initially, the benchmarks considered were the conclusions which have been published since optical communications systems first saw a major expansion.