Tight-binding calculations for the electronic structure of isolated vacancies and impurities in III-V compound semiconductors

Abstract

In the second-neighbor tight-binding framework and using the well-known $\overrightarrow{\mathrm{k}}$-space Green's-function approach, we have calculated the energies of deep highly localized electronic states due to isolated vacancies and simple point defects in III-V compound semiconductors. Using existing pseudopotential data for the band structures, we are able to calculate 21 (out of 23) interaction integrals with the help of the least-squares-fitting technique. The Green's functions in the $a_1$ ($s$-type) and $t_2$ ($p$-type) symmetries have been numerically evaluated by using the eigenfunctions and eigenvalues of the host systems. The calculated results are discussed and compared with the existing theoretical and experimental data. The pinning energies of the anion vacancy levels of $t_2$ symmetry are found to be almost the same for Ga-In pnictides while they are different for the Ga-Al and In-Al compounds. No such correlation of pinning energies due to cation vacancies has been noticed. These results provide justification to the recent experimental speculations that the anion vacancies near the surface are responsible for determining the position of the Fermi level. This also lends support to the speculation that, similar to ${\mathrm{Ga}}_{1-x}{\ln }_x\mathrm{As}\left(\mathrm{P}\right)\mathrm{}$ ternaries, the Fermi-level variation for the GaSb-InSb system should be independent of the composition factor.