An empirical potential approach to structural stability of GaNxAs1−x thin films on GaAs(1 1 1)

Structural stability of GaNxAs1−x thin films coherently grown on GaAs(1 1 1) is systematically investigated based on an empirical potential, which incorporates electrostatic energies due to bond charges and ionic charges. Using the empirical potential, the system energies of zinc blende (ZB) and wurtzite (W) structured GaNxAs1−x thin films are calculated over the entire concentration range. The calculated results predict that the structural phase transition from ZB to W occurs at xc ∼ 0.5, which differs from xc ∼ 0.7 expected by the electrostatic energy contribution dominating W-ZB polytypism in end members such as GaN and GaAs. The difference between the values of xc is clarified in terms of difference in bond lengths distribution in ZB-GaNxAs1−x and W-GaNxAs1−x. Further calculations for interface structures between ZB- or W-GaNxAs1−x thin films and GaAs(1 1 1) substrate reveal that ZB-type stacking sequence is more favorable than W-type stacking sequence at the interface. Consequently, ZB-GaNxAs1−x thin films can be fabricated in the concentration range of x < 0.5 on the GaAs(1 1 1), whereas W-GaNxAs1−x thin films are formed with ZB-type stacking interface in the concentration range of x ≥ 0.5.