Physical Simulations of Pseudomorphic InP HEMTs

Abstract

This thesis reports the development of a physical device model of an InAlAs/InGaAs/InP HEMT (High Electron Mobility Transistor). The model is developed within the frame of a semiconductor device simulation software (ISE TCAD). The influence on device operation of different, both device geometrical as well as material, parameters are examined. The impact of physical phenomena such as velocity overshoot and thermionic emission is also investigated. The models used are semi-classical in nature. Simulation results are compared to real devices manufactured in the Nanofabrication Laboratory at Chalmers University of Technology. Results show that the solution of the hydrodynamic set of differential equations are an absolute necessity for the modelling of some physical aspects of this device. Effects from lattice heating are minimal at the relatively low bias voltages considered for the InP HEMT. Simulated DC characteristics follow the general trend of experimental data. The model is, however, still too crude to predict specific results of a design modification. Comparisons of statistical models show that Fermi-Dirac statistics produces similar results to quantum models such as the Density Gradient Model and 1D Schrödinger solver. The characteristics of the band structure is shown to have large effect on DC characteristics. Structural parameters that have largest impact, are the barrier thickness and the gate length. Impact ionization is shown to be able to explain the kink effect in InP HEMT DC characteristics.