Study of structural and optoelectronic properties of Cu₂Zn(Sn_1−xGe_x)Se₄ (x = 0 to 1) alloy compounds

In this work, the optoelectronic and structural properties of Cu₂Zn(Sn_1−xGe_x)Se₄ (CZTGeSe) alloy compounds with x varying from 0 to 1 with a step of 0.1 were studied. The crystal structure and the lattice parameters of the CZTGeSe polycrystals were determined by using X-ray diffraction analysis. A linear decrease of the lattice parameter a from 0.569 nm to 0.561 nm with increasing Ge concentration was detected. Raman spectroscopy analysis revealed unimodal behavior and a linear shift of the three A symmetry Raman modes of kesterite crystal structure towards higher wavenumbers with increasing Ge content. Radiative recombination processes in CZTGeSe polycrystals were studied by using low-temperature photoluminescence (PL) spectroscopy. A continuous shift from 0.955 eV to 1.364 eV of the PL band position with increasing Ge concentration was detected. Based on the temperature dependent PL measurements of the CZTGeSe polycrystals, two types of recombination mechanisms were detected: band to impurity recombination in Cu₂Zn(Sn_1−xGe_x)Se₄ with x ≤ 0.2, and band to tail recombination in Cu₂Zn(Sn_1−xGe_x)Se₄ with x > 0.2. - Highlights: • X-ray diffraction and Raman analyses of Cu₂Zn(Sn_1−xGe_x)Se₄ were performed. • Crystal structure of Cu₂Zn(Sn_1−xGe_x)Se₄ was determined. • Temperature dependent photoluminescence of Cu₂Zn(Sn_1−xGe_x)Se₄ was measured. • Radiative recombination mechanisms in Cu₂Zn(Sn_1−xGe_x)Se₄ were identified