Effect of uncertainty in formation energies of defects in calculations for carrier concentrations in semi-insulating GaAs

In a recent communication, Deepak and Priyadarshi [Mater. Sci. Eng. B94 (2002) 20] had discussed sharp fluctuations in carrier concentrations with small changes in crystal stoichiometry of semi-insulating (SI) GaAs. That fluctuation was ascribed to be a possible cause of variations in performance of devices fabricated on SI GaAs substrate. This observation was based on estimates using formation energies of point defects calculated by first principles calculations. Since such calculations have inherent errors associated with them, it was not clear if the sharp fluctuations shown in Mater. Sci. Eng. B94 (2002) 20 are artifacts resulting from errors in formation energy data. The results presented here show, despite these errors, the sharp fluctuations in carrier concentrations are still predicted, further emphasising the need to strictly control the crystal stoichiometry to avoid variations in device performance.