Effect of donors and acceptors on the optical properties of CdGeAs ₂

CdGeAs₂ is an important nonlinear optical infrared material. Room-temperature absorption and temperature-dependent photoluminescence (PL) of as-grown p-type bulk crystals and crystals doped with indium and tellurium have been measured. The intensity of an intervalence band absorption near 5.5 μm (0.225 eV) is correlated with the intensity of a PL band near 0.55 eV. Both of these optical features indicate the presence of a native shallow acceptor level at 120 meV above the top valence band. The 0.55-eV PL band is donor-acceptor-pair recombination between shallow donors and the shallow acceptor level. A second PL band peaking near 0.35 eV is donor-acceptor-pair recombination between shallow donors and a deeper acceptor at 300 meV above the top valence band. Doping with indium and tellurium produces n-type material. The intervalence band absorption at 5.5 μm is completely eliminated in the n-type samples. Indium donors are incorporated on the Cd site and Te donors are incorporated on the As site.