First-principles studies on molecular beam epitaxy growth ofGaAs1−xBix

Abstract

We investigate the molecular beam epitaxy (MBE) growth of GaAs 1-x Bi 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 MBE species (As 2 molecule, Ga atom, Bi atom, and Bi 2 molecule) on the (2×1)-Ga sub ||Bi surface and a proposed q(1×1)-Ga sub ||AsAs surface, where Ga sub ||XY refers to a Ga-terminated GaAs(001) substrate with surface layers of X and Y. The q(1×1)-Ga sub ||AsAs surface has a quasi-(1×1) 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 MBE species 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 2 exchange with Bi of the (2×1)-Ga 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 co-deposition of all fluxes with a sequential deposition of fluxes and applying asymmetric in-plane strain to the substrate.

Impact of Disorder on the Optoelectronic Properties of GaNyAs1−x−yBix Al

“…29,31,32,67,71,72 Analysis of prototypical GaAs 1−x Bi x /GaAs QW solar cells indicates that one potential factor limiting the photovoltaic performance of lattice-matched GaN y As 1−x−y Bi x junctions may be the large inhomogeneous spectral broadening of the band edge optical absorption, associated with the presence of short-range alloy disorder and crystalline defects. 78 However, we expect that these issues could be mitigated to some degree via a combination of refinement of the epitaxial growth, 79,80 sample preparation, 81,82 and device design. This approach has been successfully employed to develop multi-junction solar cells incorporating the dilute nitride alloy (In)GaN y As 1−y , which have demonstrated record-breaking efficiency.…”

Understanding and reducing deleterious defects in the metastable alloy GaAsBi

“…12 Additionally, one might explore the pulsed laser deposition method, 53 which uses the plasma produced from bulk GaAs as the reactant and thus creates chemical potentials close to the intermediate condition.…”

“…However, the low growth temperature also induces numerous defects, which result in short carrier lifetimes and low photoluminescence intensity. 10,11 Additionally, a previous theoretical study 12 has shown that the dynamic processes associated with As substituting Bi, which limits Bi incorporation, are still extremely rapid at low temperatures, for example, o10 − 6 s at 320°C. Thermal annealing has been used to reduce the defects, but the incorporated Bi atoms often segregate and form Bi-rich clusters.…”