C- and O-incorporation in (AlGa)As epitaxial layers grown by MOVPE using TBAs

The C- and O-incorporation behaviour in (AlGa)As (0 less than or equal to x less than or equal to 1) epitaxial layers grown by metal organic vapour phase epitaxy (MOVPE) using tertiary butyl arsine (TBAs) has been investigated in detail by means of calibrated SIMS, XRD, and Hall studies. A variety of both trimethyl gallium (TMGa), trimethyl aluminum (TMAl) as well as TBAs batches has been used to grow (AlGa)As epitaxial layers in the temperature range of 625-725 degrees C using different V/III-ratios (2.5 up to 40) and reactor pressures were in the range of 50-200 mbar. The primary source of C is the methyl group of the group-ill-compounds. The C-level shows a quadratic reduction as a function of the V/III-ratio for ratios up to 10 and a smaller decline for high V/III-ratio. O-contamination in the (AlGa)As layers originates both from some batches of TMAl as well as TBAs. Two O-sources are identified in some TBAs batches due to their characteristic O-incorporation behaviour, which significantly deviates from that reported for AsH3-growth. Using specific purification steps of the TBAs these impurities were drastically reduced. State of the art low O-content (AlGa)As with O-levels of 1 x 10(18) cm(-3) for an Al-concentration of 85% and 2.5 x 10(16) cm(-3) for 30% (AlGa)As are achieved at low growth temperatures of 625 degrees C. The realization of low-O-content, high-quality (AlGa)As at low substrate temperature and almost independent of the used V/III-ratio in the MOVPE using TBAs offers new possibilities in the application of highly strained materials or critical doping layer profiles in advanced device structures, which at present are not accessible by using AsH3. (C) 1998 Elsevier Science B.V. All rights reserved.