First‐principles calculations on the origins of the gap bowing in BeS_xSe_1–x, BeS_xTe_1–x and BeSe_xTe_1–x alloys

Abstract

PACS 61.66. Dk, 71.15.Mb, 71.15.Nc, 71.22.+i First-principles calculations have been used to investigate the electronic structure and disorder effects in beryllium chalcogenides alloys (BeS x Se 1-x , BeS x Te 1-x and BeSe x Te 1-x ) using the full potential-linearized augmented-plane wave method (FP-LAPW) within density-functional theory. We used the local-density approximation within the generalized gradient correction as well as the Engel -Vosko GGA formalism to calculate the electronic structure at equilibrium volume. The ground-state properties are determined for the bulk materials (BeS, BeSe, and BeTe) as well as for the average concentration (x = 0.5) of the alloys. Using the approach of Zunger and coworkers, the microscopic origins of compositional disorder have been detailed and explained. The disorder parameter (gap bowing) is found to be mainly caused by the chemical charge-transfer effect, while the volume deformation and the structural relaxation contribute to the gap bowing parameter at smaller magnitude. This should be expected since there is a weak lattice mismatch between the binary compounds and a considerable electronegativity difference between Be and X (X = S, Se, Te) atoms.

FP‐LAPW investigations of Zn1–xBexS, Zn1–xBexSe and Zn1–xBexTe ternary alloys

“…For the Zn 1-x Be x S and Zn 1-x Be x Te alloys, we found lattice bowing parameters equal to -0.16651 and -0.13117 Å, respectively. However, violation of Vegard's law has been reported in semiconductor alloys both experimentally [25] and theoretically [26]. Figure 2 shows the bulk modulus as a function of x for Zn 1-x Be x Se alloy.…”

Structural and electronic properties of the wide-gap Zn1−xMgxS, Zn1−xMgxSe and Zn1−xMgxTe ternary alloys

“…a(A x B 1−x C) is the alloy lattice constant. However, violation of Vegard's law has been reported in semiconductor alloys both experimentally [29,30] and theoretically [31][32][33].…”

“…b SR is the structural contribution due to the relaxation of the anion-cation bond lengths in the alloy. All terms presented in equation ( 8) were computed using GGA and EVGGA; for more computational details, we refer the reader to references [32,33]. The calculated bowing parameters of the direct bandgap are presented in table 3.…”

First‐principles study of BNxSb1–x, BPxSb1–x and BAsxSb1–x alloys

“…As an example, Fig. 1 shows the variation of the calculated equilibrium lattice constants with concentration for the BN x In the treatment of alloy problems, it is assumed that the atoms are located at the ideal lattice sites and the lattice constants of alloys should vary linearly with composition x according to Vegard's law [28]; however, violations of Vegard's rule have been reported in semiconductor alloys both experimentally [29] and theoretically [30,31]. The physical origin of this large deviation for BN x Sb 1-x should be mainly due to the large mismatches of the lattice constants of BN and BSb compounds.…”