Absorption-edge anisotropy of Cu2ZnSiQ4 (Q = S, Se) quaternary compound semiconductors

Polarization-dependent absorption characterization of Cu2ZnSiQ4 (Q = S, Se) quaternary single crystal compound semiconductors were carried out in the temperature range of 10–300 K. The absorption measurements were performed on the as grown basal plane with the normal along [2 1 0] and the axis c parallel to the long edge of the crystal platelet. A significant shift towards lower energy was observed in the absorption spectra of E⊥c polarization with respect to those corresponding to E∥c polarization. A comprehensive analysis of the absorption spectra revealed that the absorption edges of the studied crystals are indirect allowed transitions. A schematic representation of the plausible assignments for the observed near band edge optical transitions for Cu2ZnSiQ4 was proposed. The variation of the indirect transition energies with temperature were analyzed by Varshni and Bose–Einstein expressions. The parameters that describe the temperature dependence of the indirect transition energies with different polarizations were evaluated and discussed.

Research highlights
► The polarization-dependent absorption characterization of Cu2ZnSiQ4 (Q = S, Se) quaternary single crystals were carried out.
► A significant shift towards lower energy was observed in the absorption spectrum of E⊥c polarization with respect to that corresponding to E∥c polarization.
► Analysis of the absorption spectra revealed that the absorption edges of the studied crystals are indirect allowed transitions.
► A schematic representation of the plausible assignments for the observed near band edge optical transitions for Cu2ZnSiQ4 was presented.