On the effect of structural disorders on the Urbach’s tails of ternary chalcopyrite semiconductors and related ordered defect compounds

Abstract

The effect of structural disorders on the Urbach's tails (UTs) in the optical absorption spectra in CuBIIIC2VI, CdBIVC2V ternary chalcopyrite semiconductors and other related CuB3IIIC5VI, CuB5IIIC8VI, and Cu3B5IIIC9VI ordered defect compounds (ODCs) is studied. Analysis of UT in such a large number of ternary compounds with the adjustable parameters P and N permits us to have a better understanding of their physical importance. These parameters are used to explain the variation of Urbach’s energy EU with temperature T. They take into account the basic effect of substitutional disorder caused by molecularity and deviation from stoichiometry and also the handicap in the thermal weight due to the distribution of the resulting additional phonon modes, respectively. They play an important role in determining quantitatively the presence of structural defects. P explains quite well higher values of hνp observed in multinary compounds, and N indicates when an order–disorder phase transition could occur in these materials. It is also found that the energy of phonons involved in the formation of the photon absorption edge hνp in ODCs is higher than that observed in normal CuBIIIC2VI chalcopyrite compounds and increases linearly as the effective cation radius reff increases in the sequence CuB5IIIC8VI→CuB3IIIC5VI→Cu3B5IIIC9VI. The analysis also suggests that the magnitude of these parameters can be very useful in device applications of these materials such as solar cells and thermoelectric power generation.