Modeling capture, emission, and impact ionization of deep-level traps for Ga-As semi-insulating substrates

A numerical model that self-consistently computes electron capture, emission, and impact ionization from deep-level traps (DLTs) is presented. A GaAs n-i-n structure with the i-region representing the semi-insulating (SI) GaAs substrate is simulated using the model. It is found that the threshold voltage (defined as the onset voltage at which the leakage current begins to rise rapidly) for substrate breakdown may be dramatically reduced by the impact ionization of DLT trapped electrons. The temperature dependence of the threshold voltage may also be explained by the impact ionization effect. The model can improve the prediction of current-voltage characteristics of a deep-level-trap compensated semi-insulating GaAs substrate under the conditions of electric field and varying temperature