Electronic and optical properties of Cu2ZnSnS4 and Cu2ZnSnSe4

Abstract

The electronic structure as well as the optical response of kesterite and stannite structures of Cu2ZnSnS4 and Cu 2ZnSnSe4 are analyzed by a relativistic full-potential linearized augmented plane wave method. The energy dispersion of the conduction-band edge reveals larger effective electron mass of the two Cu 2ZnSnS4 compounds (mc1 ≈0.18 m0) compared with Cu2ZnSnSe4 (mc1 ≈0.07 m 0). Whereas the effective electron mass tensor is fairly isotropic, the effective hole masses show strong anisotropy. The fundamental band-gap energy is estimated to be Eg ≈1.5 eV for Cu2ZnSnS 4 and Eg ≈1.0 eV for Cu2ZnSnSe4. The larger band gap results in a smaller high-frequency dielectric constant: ε∞ ≈6.7 for Cu2ZnSnS4 whereas ε∞ ≈8.6 for Cu2ZnSnSe4. The characteristic anisotropy of the dielectric function ε (ω) in the stannite compounds allows for a complementary identification of the crystalline structure type. Overall, however, all four compounds show similar atomic-resolved density-of-states, dielectric function, and optical absorption coefficient α (ω). © 2010 American Institute of Physics.