Promising transparency and p-type conductivity of Li, Na, K and Rb-doped CaS: A first-principles study

Abstract

Using the first-principles method, the transparency and p-type conductivity for CaS are investigated. Our studies indicate CaS is an indirect gap semiconductor, and the band gap along Γ-X is 3.57 eV. The hole effective mass is 0.87 m0 (m0 is the mass of the free electron). Low absorption and reflectivity, as well as high transmittance ensure its transparency in the visible light region. Group VA (IA) atoms substituting S(Ca) are deep (shallow) acceptors. Based on hybrid functionals calculations, we find the ionization energies ε(0/-) for group IA atoms substituting Ca are less than 0.15 eV above the valance band maximum. The Li2S, Na2S, K2S and Rb2S are promising impurity sources. Taking Na-doped CaS as an example, we predict the holes′ concentration can reach 1.54 × 1017cm−3 under S-rich condition. High transparency, smaller hole effective mass, low ionization energy and high concentration of holes imply that CaS is promising transparent p-type conducting material.