Influence of Bi on the temperature dependent fundamental band gap parameters of GaSb 1-x Bi x

The temperature dependent near band edge emission of LPE grown GaSbBi is studied using photoluminescence technique. A two oscillator model is used to obtain the relevant parameters that explain the temperature dependence of band gap more adequately in cryogenic region as compared to the information obtained through the conventional 'Varshni' model. The two oscillator model also provides some valuable information on the phonon dispersion co-efficient in GaSb and GaSbBi and its behavior vis-α-vis the bismuth content in the material. Calculations show that the relative contribution of the high energy LA phonon branch increases with increase in Bi concentration and dominate the temperature dependence of band gap. By considering the energy gap as Gibbs free energy of electron and hole pair formation, approximate analytical expressions are derived for the entropy and the enthalpy of the formation process. The entropy of formation of electron-hole pairs is found to decrease with Bi content in GaSbBi indicating an increase in ordering and a decrease of electron- phonon interaction which might explain the reduced temperature dependence of band gap of some III-V-bismides.