First-principles studies on molecular beam epitaxy growth of GaA s sub(1-x) Bi sub(x)

We investigate the molecular beam epitaxy (MBE) growth of GaA s sub(1-x) Bi sub(x) film using density functional theory with spin-orbit coupling to understand the growth of this film, especially the mechanisms of Bi incorporation. We study the stable adsorption structures and kinetics of the incident molecules (As sub(2) molecule, Ga atom, Bi atom, and Bi sub(2) molecule) on the (2 x 1) -Ga sub(sub)|| Bi surface and a proposed q(1 x 1) -Ga sub(sub)||AsAs surface, where Ga sub(sub)|| XY refers to a Ga-terminated GaAs(001) substrate with surface layers of X and Y. The q(1 x 1) -Ga sub(sub)|| AsAs surface has a quasi-(1 x 1) As layer above the Ga-terminated GaAs substrate and a randomly oriented As dimer layer on top. We obtain the desorption and diffusion barriers of the adsorbed molecules and also the reaction barriers of three key processes related to Bi evolution, namely, Bi incorporation, As / Bi exchange, and Bi clustering. The results help explain the experimentally observed dependence of Bi incorporation on the As / Ga ratio and growth temperature. Furthermore, we find that As sub(2) exchange with Bi of the (2 x 1) -Ga sub(sub)|| Bi surface is a key step controlling the kinetics of the Bi incorporation. Finally, we explore two possible methods to enhance the Bi incorporation, namely, replacing the MBE growth mode from codeposition of all fluxes with a sequential deposition of fluxes and applying asymmetric in-plane strain to the substrate.