Insight into physical properties of carbon-doped BeSiP2 and BeGeP2 chalcopyrite: An ab initio study

Abstract

Our present article reports the carbon substitution-driven changes in the behavior of BeSi1-xCxP2 and BeGe1-xCxP2 (x = 0.25 and 0.5) chalcopyrite alloys using the full-potential augmented plane wave plus local orbital (FP-APW + lo) based first-principles calculations. The lattice constants (a and c) of BeSi1-xCxP2 and BeGe1-xCxP2 are shortened, and the bulk moduli are improved as carbon atoms replace Si and Ge atoms. The computed negative formation energy (Ef) indicate adequate thermodynamic stability of the BeSi1-xCxP2 and BeGe1-xCxP2 alloys. The bandgaps pristine BeSiP2 and BeGeP2 computed as 1.84 eV and 1.54 eV, respectively, using the modified Tran-Blaha (TB) Becke Johnson (mBJ) transition potential, matching well to the experimental results. However, the C substitution is found to narrow the bandgap of BeSiP2 and BeGeP2 considerably. Similarly, C substitution is found to reduce electrons' and holes’ effective mass and enhance the absorption coefficient of BeSi1-xCxP2 and BeGe1-xCxP2 alloys up to (α∼105cm−1). Our predictions indicate that the physical properties of BeSiP2 and BeGeP2 chalcopyrite can be modified effectively by replacing C in the Si and Ge sites, which makes them promising for optoelectronic applications.