Pitch-induced bandgap tuning in self-catalyzed growth of patterned gaassb axial and GaAs/GaAsSb core-shell nanowires using molecular beam epitaxy

We report on the pitch-induced bandgap tuning in GaAsSb (axial) and GaAs/GaAsSb (core-shell) patterned vertical nanowire (NW) arrays grown by Ga-Assisted molecular beam epitaxy on Si(111). Red shifts in the range of 40-50 meV in the 4 K micro-photoluminescence (μ-PL) spectral peaks have been observed, for NW arrays with pitch length variation from 200 to 1200 nm, in the axial and core-shell configurations. The variation in the PL peak intensity closely follows the optical absorption dependency on the pitch length of the NW array computed using finite dimension time domain simulation. A semiempirical mass conservation of the growth-species-based-model has been proposed encompassing different material pathways. The secondary fluxes re-emitted from the side facets of the neighboring NWs contribute substantially toward the growth for smaller pitch lengths, while those from the oxide surface dominate at larger pitch lengths for high V/III beam equivalent pressure ratios. Excellent agreement between the experimental and simulated results have been observed for the pitch dependent axial and radial NW dimensions of both the axial and core-shell configured GaAsSb NWs. This study shows great promise for the applicability of patterned NWs for band gap tuning by simply varying the NW array pitch length.