First principles-based study about electronic, optical, and transport nature of novel A2ZnSe2 (A = K and Na) materials

Abstract

Here we studied, the cationic alkali metal-based ternary type Chalcogenides for their optoelectronic and thermoelectric nature by using the state-of-the-art density functional theory. The computed bandgap exposed the fact that the studied materials are semiconductors in nature. The predicted band gap values for K2ZnSe2 were 2.351 ​eV and 2.164 ​eV for Na2ZnSe2 material. Furthermore, the revealed valence band maxima and the conduction band minima that lies at the Г-point of the Brillouin zone indicated a direct bandgap nature in these materials. The existence of flat bands close to Fermi level in the valence band proclaimed that these materials also have interesting applications in electronic devices. The computed density of states for K2ZnSe2 and Na2ZnSe2 well support the result of the band structures and confirm their semiconducting nature. Each Zn and Se atom possesses a major contribution in the formation of the valence band in both the materials, however near the Fermi level in the valence band the Se chalcogen atom shows a dominant role. In the case of K2ZnSe2, the computed values of ε1xx (0) and ε1zz (0) are about 4.1 and 4.7 respectively whereas for Na2ZnSe2 the observed values are 5.1 and 5.8 fits well with Penn’s criteria. The inexistence of absorption in the visible region also confirms the studied materials to be promising candidates for optoelectronics. The thermoelectric characteristics such as the Seebeck coefficient, specific heat capacity, thermal conductivity, the power factor (PF), and the figure of merit as a function of temperature were also examined and studied for their possible thermoelectric device applications.