Sharp fluctuations in carrier concentrations with small changes in crystal stoichiometry of semi-insulating GaAs

Our calculations to investigate the role of stoichiometry of GaAs are based on the assumption of thermodynamic equilibrium of point defects at an elevated temperature and then the redistribution of the charge states of the quenched-in defects at room temperature. The effect of stoichiometry of semi-insulating (SI)-GaAs crystal on carrier concentration is well known, especially the change from p-type to SI behavior as the crystal changes from Ga rich to As rich. Our detailed calculations confirm this, but in addition show that the sudden decrease in carrier concentration is followed by an equally sharp increase before becoming relatively constant at a value typical of As rich SI substrates. We are not aware of measurements that have detected this increase in carrier concentration, presumably due to difficulty in accurately controlling the crystal stoichiometry. However, this effect is likely to have an enormous impact in device processing, and hence, needs to be further looked into experimentally. Also, since the primary purpose for developing this model is to make it available for GaAs Technology Computer Aided Design (TCAD) tools, we have only made those assumptions that ensure effortless integration with them. We also discuss the calibration methodology for use of the model in TCAD based process and device design.