Bandgap tuning of GaAs/GaAsSb core-shell nanowires grown by molecular beam epitaxy

Abstract

Semiconductor nanowires have been identified as a viable technology for next-generation infrared (IR) photodetectors with improved detectivity and detection across a range of energies as well as for novel single-photon detection in quantum networking. The GaAsSb materials system is especially promising in the 1.3-1.55 μm spectral range. In this work we present bandgap tuning up to 1.3 μm in GaAs/GaAsSb core-shell nanowires, by varying the Sb content using Ga-assisted molecular beam epitaxy. An increase in Sb content leads to strain accumulation in shell manifesting in rough surface morphology, multifaceted growths, curved nanowires, and deterioration in the microstructural and optical quality of the nanowires. The presence of multiple PL peaks for Sb compositions 12 at.% and degradation in the nanowire quality as attested by broadening of Raman and x-ray diffraction peaks reveal compositional instability in the nanowires. Transmission electron microscope (TEM) images show the presence of stacking faults and twins. Based on photoluminescence (PL) peak energies and their excitation power dependence behavior, an energy-band diagram for GaAs/GaAsSb core-shell nanowires is proposed. Optical transitions are dominated by type II transitions at lower Sb compositions and a combination of type I and type II transitions for compositions 12 at.%. Type I optical transitions as low as 0.93 eV (1.3 μm) from the GaAsSb for Sb composition of 26 at.% have been observed. The PL spectrum of a single nanowire is replicated in the ensemble nanowires, demonstrating good compositional homogeneity of the latter. A double-shell configuration for passivation of deleterious surface states leads to significant enhancement in the PL intensity resulting in the observation of room temperature emission, which provides significant potential for further improvement with important implications for nanostructured optoelectronic devices operating in the near-infrared regime.

Effects of Annealing on GaAs/GaAsSbN/GaAs Core-Multi-shell Nanowires

“…Both the Sb and N shutters were closed for growth of the final GaAs shell at 540 °C. Detailed growth procedures and characterization techniques are provided in our previous reports [ 11 , 13 , 14 ]. Basically, TEM, PL, and Raman were used to reveal differences in these nanowires before and after annealing.…”

Measurements of Strain and Bandgap of Coherently Epitaxially Grown Wurtzite InAsP–InP Core–Shell Nanowires

“…positions of the group-III and group-V atomic layers, which has potential use in making novel photovoltaic devices [36][37][38][39][40][41][42]. Other uses of the effects of coherent strain in core-shell nanowires include strain induced bandgap tuning [18,30,33,34,43] and increased carrier mobilities [33].Here we report on epitaxial growth of wurtzite (WZ) InAsP-InP core-shell nanowires in a series of shell thicknesses and measurements of strain and optical properties of the nanowires.These materials are of great interest for high speed infrared optoelectronics operated in the telecommunication wavelength window (1.3-1.5 µm), since the bandgap of InAsP can be tuned by compositions from 0.35 to 1.34 eV, corresponding to optical wavelengths from 3.5 µm to 0.9 µm.The WZ InAsP-InP core-shell nanowires are grown by metal-organic vapor phase epitaxy (MOVPE). The lattice parameters of as-grown nanowires are measured by X-ray diffraction (XRD), from which the strain is extracted.…”

“…positions of the group-III and group-V atomic layers, which has potential use in making novel photovoltaic devices [36][37][38][39][40][41][42]. Other uses of the effects of coherent strain in core-shell nanowires include strain induced bandgap tuning [18,30,33,34,43] and increased carrier mobilities [33].…”

Epitaxially grown III-arsenide-antimonide nanowires for optoelectronic applications

“…[57,58] Efforts have been made using core-shell structured GaAsSb NWs to achieve optical emission in the telecom wavelength band, and photoluminescence (PL) emission at ~1.3 μm has been observed by tuning the growth temperature and V/III ratio for both GaAs/GaAsSb and GaAs/GaAsSbN systems. [59,60] By further growth of a double-shell configuration, the optical emission intensity can be further enhanced. [60] Other than the GaAs/GaAsSb core-shell structure, GaSb/InAsSb and GaAsSb/InAs systems have also attracted a lot of attention due to their interesting electrical behavior.…”