CHARACTERIZATION OF DEEP CENTERS IN UNDOPED SEMIINSULATING GAAS SUBSTRATES BY NORMALIZED THERMALLY STIMULATED CURRENT SPECTROSCOPY - COMPARISON OF 100 AND 150 MM WAFERS

A well-established characterization method for investigating deep trap s in semiinsulating (SI) GaAs is thermally stimulated current(TSC) spe ctroscopy; however, TSC is not considered to be a quantitative techniq ue because it involves carrier mobility, lifetime, and geometric facto rs, 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 s tudy the lateral uniformity of the main deep centers across the diamet ers of undoped SI GaAs wafers. The wafers used in the study include bo th the standard 100 mm sizes and the new 150 mm variations, and are gr own by both the low and high pressure liquid encapsulated Czochralski techniques. The results reveal that the 150 mm wafers have a worse NTS C uniformity for the main traps and a higher degree of compensation, a s compared these parameters for the 100 mm wafers. In addition, nonuni formities related to the electric field effects on both the TSC spectr um and the low temperature photocurrent are found in the 150 mm wafer grown by the low pressure technique.