Analysis of Patterned GaAsSbN Nanowires via Boltzmann Sigmoidal Model

Abstract

Abstract Body: The first reports of applying the Boltzmann Sigmoidal model on pitch-dependency in patterned nanowires (NWs) of dilute nitride GaAsSbN on p-Si (111) substrates by self-catalyzed plasma-assisted molecular beam epitaxy are presented in this study. Morphological and structural characterizations of the patterned NWs are accomplished via field emission scanning electron microscope (FESEM) and high-resolution transmission electron microscope (TEM), respectively. Top, middle, and bottom NW segments captured via selected area electron diffraction (SAED) characterization confirmed the single-crystal zincblende structure of the NWs. The absence of satellite spots in the SAED pattern indicates the NWs are free of planar defects. Sizeable bandgap tuning of ~75 meV, as ascertained from 4K photoluminescence (PL), is demonstrated over a pitch length variation of 200 nm to 1200 nm. Axial and radial growth rates reveal a logistic sigmoidal growth trend with respect to pitch, which differs from those commonly observed in other patterned non-nitride III-V NWs. The Boltzmann sigmoidal model offers additional insight into the shift of the PL spectral arising from differences in Sb and N incorporation from pitch induced variation in secondary fluxes. The extracted inflection points, p0, of 636 nm and 806 nm, for axial growth rate correlate very well with the homogeneous broad peaks revealed by PL analysis at these pitch lengths. Furthermore, the inflection point indicates the pitch length where the pitch dependent effects on the secondary fluxes play a prominent role in axial and radial growth of patterned NWs. Additionally, the values of the sigmoidal slope, α, correlate well with the range of pitches where Sb and N incorporation are observed with broad PL spectra. Results indicate that the extracted parameters obtained via the sigmoidal model of inflection point, and slope can be used as a rubric for optimal pitch length for patterned array design of homogeneous nitride NWs and can be extended to other highly mismatched alloy compounds. This work is financially supported by National Science Foundation (Award No. 1649517) and through the Title III HGBI Ph.D. Fellowship.