Characterization of si-GaAs wafer quality by room-temperature photoluminescence

The mapping of near-band-gap photoluminescence intensity is used as a method for characterizing the uniformity of wafer properties which is an essential requirement for fabrication of integrated circuits on si-GaAs substrates.

The surface effects on PL intensity and uniformity were investigated directly after an oxide removal etch and after storage of wafers under dark and illuminated conditions. Storage results in a decrease of the PL intensity and the PL contrast. This is probably associated with changes in the native oxide composition. PL changes during storage can be reversed by suitable oxide etching and cleaning which is important for obtaining reproducible results on wafer uniformity.

The bulk PL uniformity was studied in dependence on post-growth thermal treatments and distinct improvements in PL uniformity across a wafer were found due to various annealing conditions. Very low variations of < 10% are obtained by an optimized annealing process even up to 100 mm diameter wafers. High-resolution measurements show that these changes in wafer uniformity are correlated to characteristic microscopic changes within the well known cell structure.