Effect of interfacial bond type on the electronic and structural properties of GaSb/InAs superlattices

Abstract
We have investigated the effects of interfacial bond configuration on the electronic and structural properties of thin (001)GaSb/InAs superlattices by using state-of-the-art ab initio molecular dynamics techniques to calculate the electronic and structural properties of two twelve-atom model GaSb/InAs superlattices which have been constructed to contain only In–Sb (model 1) or Ga–As (model 2) interface bonds, respectively. We find the strain at the the interface to be different in the two cases. In model 1, the In and Sb atoms at the interface move away from each other toward the InAs and GaSb layers, respectively, increasing the interfacial separation (4.3% greater than in bulk InSb) and compressing the back bonds to the atoms in the layer below the interface. In model 2 the Ga and As atoms move toward each other, decreasing the interplanar separation at the interface (3.2% smaller than in bulk GaAs) and stretching the back bonds to the neighboring Sb and In atoms, respectively. We calculate the valence band offset for the Ga–As bonded structure to be 0.15 eV smaller than that for the model containing only In–Sb bonds. This smaller band offset leads to more mixing of As p character into the highest lying valence band of the superlattice and results in a 0.015 eV smaller spin-orbit splitting at the valence band edge of the Ga–As bonded structure. This result is consistent with the 0.05 eV larger band gap observed for Ga–As bonded structures in recent photoconductivity measurements made on both Ga–As and In–Sb bonded samples grown by molecular-beam epitaxy.

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