Temperature variation of the fundamental absorption edge in AgGaSe2

Optical absorption measurements were made in the temperature range 9–300 K on the chalcopyrite semiconductor compound AgGaSe₂ and the optical energy gap E_G determined as a function of temperature T. In order to obtain the values of E_G as a function of T, the Elliot-Toyozawa model [R.J. Elliot, J. Phys. Rev. 108 (1957) 1384; D.D. Sell, P. Lawaets, Phys. Rev. Lett. 26 (1971) 311] was employed to perform the analysis of the optical absorption spectra. The resulting E_G vs. T curve was fitted to a semi-empirical model that takes into account both the thermal expansion and the electron–phonon interaction contributions. The results have been used to estimate values of the deformation potentials of the valence and conduction bands of the compound.