Low Temperature Photoluminescence from Dilute Bismides

We report on photoluminescence measurements of GaAs (1-x) Bix thin films containing dilute concentration (x0.045%) of isoelectronic impurity Bi. At a temperature of 4 K, we observed a sharp emission line at ∼1.510 eV and a series of undulations in an energy range of ∼20 meV below it. We attribute the sharp line at ∼1.510 eV to the recombination of excitons bound to a complex formed by unintentionally incorporated acceptor or donor atoms in the samples. Undulations observed below the sharp line at 1.510 eV are assigned to the vibronic levels of the acceptors, generated by the dynamic Jahn-Teller effect due to the coupling between the holes bound to Bi and acceptors. The sharp line at ∼1.510 eV and the undulation peaks show a redshift with increasing Bi concentration due to the decrease in band gap as a result of the strong perturbation to the GaAs band structure induced by isoelectronic Bi impurities. No spectral evidence for isolated Bi forming a bound state in GaAs was seen and similar to the case of Bi in GaP, no Bi-Bi pair states were observed.