Pressure dependence of defects and p-d hybridization in chalcopyrite semiconductors

We have studied the effect of pressure on optical transitions involving defects in the photoluminescence spectra of two chalcopyrite semiconductors AgGaS₂ and CuGaS₂. In the former compound results obtained in samples doped with either Cd or Au are compared with unintentionally doped samples. In both compounds we find transitions whose pressure coefficients are larger than that of the band gap. We have identified these transitions as involving deep acceptors. We propose that in the chalcopyrite semiconductors the valence-band edge can be less pressure dependent than the deep acceptors because of p-d hybridization in the valence-band wave functions.