Conduction-band-edge charge densities in elemental and compound semiconductors

Abstract

The empirical pseudopotential method is used to compute electronic charge densities at the \ensuremath{\Gamma}, L, and X k points of the conduction-band edge in selected group-IV elemental (Si, Ge, \ensuremath{\alpha}-Sn) and III-V compound (GaP, GaAs, GaSb, InP, InAs, InSb) semiconductors. We find that these charge distributions are essentially independent of the system under study and are strongly dependent upon the symmetry of the wave function of a particular state. As a direct consequence of this analysis, we find that the ${\ensuremath{\Gamma}}_{1}^{c}$ conduction-band state for the heteropolar semiconductors contains an abundance of charge density associated with the anion as opposed to the cation in support of a previous observation by Baldereschi and Maschke, and that the symmetry of the wave function of the conduction-band edge at ${X}^{c}$ for GaSb is actually ${X}_{3}^{c}$, and not ${X}_{1}^{c}$ as has been previously assigned in the literature. We therefore predict an increase in both the direct and indirect band gaps of the Nowotny-Juza alloy \ensuremath{\alpha}-LiZnSb upon applying the interstitial insertion rule of Wood, Zunger, and de Groot to GaSb.