Exciton-phonon coupling in individual GaAs nanowires studied using resonant Raman spectroscopy

Abstract

The Fröhlich coupling strength of individual GaAs nanowires is investigated by resonant micro-Raman spectroscopy measurements near the direct bandgap E g . Large 2LO/1LO intensities up to 5.7 are observed in an individual GaAs nanowire. A 2LO resonance profile of the GaAs nanowire agrees well with a two-phononscattering model, suggesting excitonic scattering. These results advance the understanding of electron-phonon coupling and exciton scattering in quasi-one-dimensional systems and in GaAs at E g , allowing for the development and optimization of nanowire optoelectronic devices. DOI: 10.1103/PhysRevB.80.201314 PACS number͑s͒: 63.22.Gh, 63.20.kd, 71.35.Ϫy, 78.30.Fs Nanowires are quasi-one-dimensional crystals that can exhibit radial quantum confinement, resulting in nanoscale properties different from those of the bulk. Individual semiconductor nanowires have been employed in nanoscale optoelectronic devices, such as electrically driven lasers, 1 lightemitting diodes, 2 and photodetectors, 3 among other applications. 4 A fundamental understanding of electronphonon interaction within nanowires is required to tailor their optical and electrical properties 5 and could further the development of nanowire electronic devices. For example, photoluminescence peak broadening is largely attributed to the coupling of electronic charge to phonons, 6 which can inhibit the ability to spectrally distinguish individual photons; further, phonon coupling to the electron of a bound exciton could drastically affect optoelectronic properties in nanowire devices, especially in regimes of strong quantum confinement. 7,8Fröhlich-induced electron-phonon coupling in assemblies of nanowires has been previously investigated under nonresonance conditions. 9,10 However, a disparity in growth directions, size, and structure of nanowires within an assembly can result in averaged spectral data hindering information on a single-nanowire level. Resonant Raman spectroscopy is sensitive to structural variations of individual nano-objects within a population, 11 but no resonant Raman studies on individual nanowires have been reported to date. Here, we study individual nanowires by resonant micro-Raman spectroscopy near the energy bandgap E g to understand electronphonon coupling and exciton scattering in quasi-onedimensional systems. Notably, previous attempts have been hampered by excessive photoluminescence ͑PL͒.12 A model is presented for two-phonon excitonic scattering, which fits well with the observed 2LO resonance intensities from a single GaAs nanowire and allows us to assess the Fröhlich coupling strength and the exciton damping constant.GaAs nanowires were grown using metalorganic chemical vapor deposition catalyzed by 90 nm Au nanoparticles, as reported previously.13 Nanowire structural properties were investigated using a JEOL 6320FV high-resolution scanning electron microscope ͑SEM͒ and by JEOL 2010F fieldemission transmission electron microscope ͑TEM͒. For Raman experiments, nanowires were removed from the growth substrates by so...

Determination of the band gap and the split-off band in wurtzite GaAs using Raman and photoluminescence excitation spectroscopy

“…36,37 Under resonant conditions, not only the intensity of the dipole-forbidden A 1 (LO) mode at ∼290 cm −1 increases significantly but also the second order Raman scattering by two A 1 (LO) phonons at ∼580 cm −1 is strongly enhanced. 38 For simplicity, in the following we will denominate the A 1 (TO) and A 1 (LO) modes as simply TO and LO. Now we proceed with the determination of the resonance Raman conditions for the measurement of the critical points of wurtzite GaAs.…”

Polarized zone-center phonon modes of wurtzite GaAs

“…This choice of excitation strongly enhances scattering by the LO phonon, but is still far from the expected outgoing resonance condition itself. 16,17 While in general the TO ͑LO͒ phonon is backscattering-forbidden from ͕100͖ ͕͑110͖͒ zincblende surfaces, it is allowed from ͕110͖ ͕͑100͖͒ ones, so that the choice of a cleaved ͕110͖ surface of an undoped zincblende ͓001͔ epilayer reference sample grown by molecular beam epitaxy makes the TO phonon visible by the usual selection rules 14 and the otherwise-forbidden LO one strongly visible because of the resonance ͑band gap͒ proximity. 16 The background resulting from the sample PL has been subtracted from all of the spectra in Fig.…”

Double strain state in a single GaN/AlN nanowire: Probing the core-shell effect by ultraviolet resonant Raman scattering

“…In particular, unusual angular dependencies of the vibrational modes can be evidenced in relation with the highly anisotropic shape of the NWs. Exciton scattering has also been found to be the main effect contributing to the electron-phonon coupling by a resonant Raman scattering study 7 in single GaAs NWs. The strain study in single NW has recently benefited of original approaches such as the analysis of bent semiconductor NWs 8 and uninentional core-shell structures.…”

“…Inelastic light scattering spectroscopy has been intensively applied to single GaAs, AlGaAs and InP NWs [6][7][8][9] with a special attention paid to the polarization, resonance, structural and strain effects. In particular, unusual angular dependencies of the vibrational modes can be evidenced in relation with the highly anisotropic shape of the NWs.…”