Impact ionization in InP-based HEMTs

Abstract

A physical model of impact ionization in InP HEMTs is developed and incorporated in a.n equivalent circuit model for comparison with experiment a1 observations showing excellent agreement. Impact ionization is modeled by a voltage dependent current source in an RC network at the drain end. The RC branch behaves like a low pass filter that imparts a frequency dependence to the impact ionization current source and enables one to model the inductive nature of S22 at low frequencies. Theoretical calculations show a compression of transconduct ance due to impact ionization with increasing gate bias that is supported by experimental data. Finally, an experimental method is suggested to extract impact ionization induced transconductance using YZl.