Free-exciton-impurity interaction in AlAs

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Abstract
The intrinsic band edge of AlAs at 10 K has been studied in optical absorption using the wavelength-modulation technique. The results show at the free-exciton energy fine structure not previously observed. It is found that the strength of the fine structure is related to the doping of the AlAs. Two of the peaks in the derivative spectrum and their phonon replicas appear to be related to Si and S impurities. It is hypothesized that these peaks are resonant exciton states in the free-exciton continuum resulting from an interaction between impurities and free excitons.