Suppression of the anomalous blue shift in the band gap temperature dependence of AgCuGaS2 alloys

It has been known for some time that, at temperatures below 100 K, the band gap of AgGaS₂ exhibits an anomalous blue shift with increase in temperature. We have found that this anomalous blue shift can be suppressed completely by as little as 1% of Cu in AgCuGaS₂ alloys. In conjunction with the disappearance of the blue shift, soft-phonon sidebands to the one-phonon Raman peaks are greatly broadened and no longer resolvable as distinct peaks. Our results are consistent with the suggestion that a soft-phonon mode may be responsible for this anomalous blue shift in AgGaS₂.