Photoluminescence of n-type CdGeAs₂

Samples of n-type CdGeAs₂ were produced by intentional doping with indium, selenium, or tellurium impurities. A near-edge photoluminescence (PL) band from heavily In-doped CdGeAs₂ samples shifts to higher energy and becomes broader with increasing electron concentration. The observed shifts in peak energies are compared to predictions for donor-acceptor pair and free-to-bound (electron-acceptor) recombinations including band filling, band tailing, and band gap shrinkage effects due to the high doping levels. For n>2 × 10¹⁸ cm^-3, the free-to-bound PL transition related to a shallow 120 meV acceptor level is dominant. A lower energy PL band due to deep acceptors and normally seen for p-type samples is the only emission observed from less n-type samples (n∼10¹⁶-10¹⁷ cm^-3) doped with indium, selenium, or tellurium impurities. Transitions involving the deep acceptor level are not present in the PL for heavily In-doped CdGeAs₂ crystals, which suggests that the deep acceptor may be a Cd vacancy.