Electronic and optical properties of Cu2ZnSnS4 and Cu2ZnSnSe4

The electronic structure as well as the optical response of kesterite and stannite structures of Cu2ZnSnS4 and Cu2ZnSnSe4 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 Cu2ZnSnS4 compounds (m(c1)approximate to 0.18m(0)) compared with Cu2ZnSnSe4 (m(c1)approximate to 0.07m(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 E-g approximate to 1.5 eV for Cu2ZnSnS4 and E-g approximate to 1.0 eV for Cu2ZnSnSe4. The larger band gap results in a smaller high-frequency dielectric constant: epsilon(infinity)approximate to 6.7 for Cu2ZnSnS4 whereas epsilon(infinity)approximate to 8.6 for Cu2ZnSnSe4. The characteristic anisotropy of the dielectric function epsilon(omega) 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 alpha(omega). (C) 2010 American Institute of Physics. [doi:10.1063/1.3318468]