Opto-electronic properties of gallium chalcogenides

A study of opto-electronic properties of gallium chalcogenides (GaS, GaSe and GaTe) is presented here. An investigation into the various effective charge parameters ($\text{Z}{}_{\mathrm{<mtext>eff</mtext>}}\text{, e}{}^1{}_{\mathrm{s}}\text{, e}{}^1{}_{\mathrm{T}}\text{and}\text{e}{}^1{}_{\mathrm{i}}$ and their correlation with ionicity have been done. The energy dependence of optical effective charge parameter (n_eff) have been discussed with respect to the band structure of respective chalcogenides. The low frequency optical dielectric constants (?₀₀) have been derived using reflectivity data and the obtained values of ?₀₀ have been found in agreement with the values obtained using Moss relation as also with the reported experimental data. The difference in the arrangement of fundamental structures of GaS and GaSe on one hand and GaTe on the other hand does not seem to effectively change the opto-eleetronic properties and the fundamental structure (which is common in all the three chalcogenides) is mainly responsible for determining these properties. The effect of surface conditions on the values of n_eff and ?∞ have been evaluated for GaTe. Using derived values of n_eff and ?_∞ the value of Penn gap have been determined. The Penn gap thus obtained is shown to be in agreement with the reflectivity data. In the passing we also show that essentially the Varshni formula explains fairly well the temperature dependence of the energy gap for gallium chalcogenides and the constants involved are evaluated.