Application of extended Hückel theory to GaAs, GaP, GaAs: N, and GaP: N

Extended Hückel theory is applied to GaP, GaAs, and to the nitrogen isoelectronic trap in GaP and GaAs. The theory confirms the $A_1$-symmetric nature of the N-trap electron state $N_X$ (the $A$ line in GaP) and lends support to the expectation that even small inward relaxation of the neighboring Ga atoms significantly lowers the $N_X$ binding energy (∼2 eV/Å). When compared with the results of Hsu's phenomenological one-band model, the present calculations indicate that a quantitative theory of the N trap (and all deep traps) in $\mathrm{Ga}{\mathrm{As}}_{1-x}{\mathrm{P}}_x$ must accurately account for the electronic structure of both the valence and the conduction bands.