Raman Scattering from GaAs Nanowires Grown by Molecular Beam Epitaxy

Abstract

Self-assembled nanowires have attracted much attention due to their potential applications in electronics and optoelectronics. A recent interest in Mn catalyzed GaAs nanowires are due to their potential use in spintronic devices at nanoscale. High densities of Au- and Mncatalyzed self-assembled GaAs nanowires (NWs) with diameter in the range of 20 to 200 nm and length of few microns were synthesized by molecular beam epitaxy (MBE) on different substrates at varied substrate temperatures. These nanowires were investigated by means of μ-Raman spectroscopy at room temperature. The Raman spectra from NWs show an energy downshift and a broadening of the LO and TO phonon lines that differ from those of epitaxial GaAs. We suggest that those downshift and broadening are due to the relaxation of the q=0 selection rule in the presence of structural defects in the nanowires. The results indicate that the use of Mn instead of Au as growth catalyst does not affect the structural quality of the nanowires drastically.

Low temperature photoluminescence and Raman phonon modes of Au-catalyzed MBE-grown GaAs–AlGaAs core–shell nanowires grown on a pre-patterned Si (111) substrate

“…In general, the phonon modes showed downshift, asymmetrical broadening and intensity ratio of LO/TO less than 1. These are characteristics of NWs that have previously been reported [33][34][35]. Fig.…”

“…The downshift cannot be due to confinement effects as diameter of the nanowires is greater than the GaAs Bohr radius, and is not also due to the encapsulation condition as the bare NW samples showed a similar shift in phonon modes. Other mechanisms that explain the downshift are the shape effect [34] and lattice defect [35]. According to Mahan et al [34], the shape effect can explain the downshift and asymmetrical broadening in phonon modes.…”

“…In our case, both the TO and the LO modes downshifted, and the shift in LO is larger than what Mahan et al have observed. In another report, Begum et al [35] presented that the energy downshift of TO and LO phonon modes was due to defects within the wire. In their paper, they have observed as much as 1.3-2.0 and 3.2-5.8 cm À 1 downshift for TO and LO modes, respectively.…”

A Study of GaAsSb Nanowires by Molecular Beam Epitaxy for Near IR Applications

“…In the NW samples, the spectra exhibit GaAs-like TO and LO phonon modes at 266 and at 289 cm −1 , respectively, which are in good agreement with the corresponding bulk GaAs values. Compared to the reference epitaxial film, however, the GaAslike TO and LO modes in the NWs are shifted upward by 10-11 cm −1 , which are opposite to the downshift in energy reported [44] in GaAs NWs. The FWHM of the GaAs-like TO and LO modes in NWs N1 and N2 are 8/8 cm −1 and 8/11.1 cm −1 , respectively.…”

Phonon Confinement Effect in III-V Nanowires

“…The excitation source was 514.5 nm line of an Ar + ion laser with a spot diameter of about 400 nm and excitation density of 1.67 mW/µm 2 for GaAs NWs and 0.56 mW/µm 2 for InAs NWs. Other details of NWs growth and Raman experimentation can be found in reference [7,[18][19][20][21]. In order to measure the light scattered by single nanowires, after the growth, the wires were mechanically transferred onto a Si substrate.…”