Modeling and Simulation of Capacitance–Voltage Characteristics of a Nitride GaAs Schottky Diode

A nitride GaAs Schottky diode has been fabricated by the nitridation of GaAs substrates using a radio frequency discharge nitrogen plasma source with a layer thickness of approximately 0.7 nm of GaN. The capacitance–voltage ( C – V ) characteristics of the Au/GaN/GaAs structure were investigated at room temperature for different frequencies, ranging from 1 kHz to 1 MHz. The C – V measurements for the Au/GaN/GaAs Schottky diode were found to be strongly dependent on the bias voltage and the frequency. The capacitance curves depict an anomalous peak and a negative capacitance phenomenon, indicating the presence of continuous interface state density behavior. A numerical drift–diffusion model based on the Scharfetter–Gummel algorithm was elaborated to solve a system composed of the Poisson and continuities equations. In this model, we take into account the continuous interface state density, and we have considered exponential and Gaussian distributions of trap states in the band gap. The effects of the GaAs doping concentration and the trap state density are discussed. We deduce the shape and values of the trap states, then we validate the developed model by fitting the computed C – V curves with experimental measurements at low frequency.