Luminescence and optical absorption study of p-type CdGeAs2

A photoluminescence (PL) study has been performed at liquid-helium temperature on a set of over 50 p-type bulk single-crystal samples of CdGeAs2. As part of the study, the effect of surface preparation on PL emission was evaluated. Room-temperature optical absorption measurements that monitored the intensity of the intervalence band transition peaking near 0.22 eV (i.e. 5.5 mum) were compared with the low-temperature PL data. Every sample exhibited a PL band near 0.35 eV related to a deep acceptor. A second PL band near 0.55 eV was present in all of the samples having a large absorption band, but was observed in only a few samples with an absorption coefficient less than 3 cm(-1) at 0.22 eV. We attribute this second band to donor-acceptor-pair recombination involving a shallow 120 meV acceptor and residual donor impurities. To produce low-absorption material for use in nonlinear optical devices, it is necessary to reduce the concentration of both acceptors or, alternatively, to dope with donor impurities that provide compensation.