Characterization of deep centers in undoped semi-insulating GaAs substrates by normalized thermally stimulated current spectroscopy: Comparison of 100 and 150 mm wafers

A well-established characterization method for investigating deep traps in semi-insulating (SI) GaAs is thermally stimulated current (TSC) spectroscopy; however, TSC is not considered to be a quantitative technique because it involves carrier mobility, lifetime, and geometric factors, which are either unknown or poorly known. In this paper, we first show how to quantify a TSC spectrum, by normalizing with infrared (hv = 1.13 eV) photocurrent, and then apply this method (called NTSC) to study the lateral uniformity of the main deep centers across the diameters of undoped SI GaAs wafers. The wafers used in the study include both the standard 100 mm sizes and the new 150 mm variations, and are grown by both the low and high pressure liquid encapsulated Czochralski techniques. The results reveal that the 150 mm wafers have a worse NTSC uniformity for the main traps and a higher degree of compensation, as compared these parameters for the 100 mm wafers. In addition, nonuniformities related to the electric field effects on both the TSC spectrum and the low temperature photocurrent are found in the 150 mm wafer grown by the low pressure technique.