Raman spectroscopy of wurtzite and zinc-blende GaAs nanowires: Polarization dependence, selection rules, and strain effects

Abstract

Polarization-dependent Raman scattering experiments realized on single GaAs nanowires with different percentages of zinc-blende and wurtzite structure are presented. The selection rules for the special case of nanowires are found and discussed. In the case of zinc-blende, the transversal optical mode E 1 ͑TO͒ at 267 cm −1 exhibits the highest intensity when the incident and analyzed polarization are parallel to the nanowire axis. This is a consequence of the nanowire geometry and dielectric mismatch with the environment, and in quite good agreement with the Raman selection rules. We also find a consistent splitting of 1 cm −1 of the E 1 ͑TO͒. The transversal optical mode related to the wurtzite structure, E 2 H , is measured between 254 and 256 cm −1 , depending on the wurtzite content. The azimuthal dependence of E 2 H indicates that the mode is excited with the highest efficiency when the incident and analyzed polarization are perpendicular to the nanowire axis, in agreement with the selection rules. The presence of strain between wurtzite and zinc-blende is analyzed by the relative shift of the E 1 ͑TO͒ and E 2 H modes. Finally, the influence of the surface roughness in the intensity of the longitudinal optical mode on ͕110͖ facets is presented.

Polarized and resonant Raman spectroscopy on single InAs nanowires

“…For instance, for cubic GaAs nanowires grown in the [111] direction, it was reported that the TO Raman signal is much stronger for the x(z,z)x than any other configuration. 13 This suggests that the contribution of the zinc-blende structure is weak and may only contribute in the x(z,z)x configuration, which, in our case, is partly a factor of 2 weaker than the x(y,y)x configuration.…”

“…[7][8][9][10] In this paper, we use first-order polarized Raman scattering and resonant Raman scattering to investigate single InAs nanowires. First-order polarized Raman scattering have been recently used to investigate GaN, 11,12 GaAs, 13,14 GaP, 15 ZnO, 16 RuO 2 , 17 and CdS (Ref. 18) single one-dimensional nanostructures.…”

Morphology and composition of oxidized InAs nanowires studied by combined Raman spectroscopy and transmission electron microscopy

“…The spectra of the nonoxidized NW is identical to bulk InAs and contain one main peak at ∼216 cm −1 assigned to the InAs transverse optical (TO) phonon mode and a weak side-peak at 237 cm −1 assigned to the longitudinal optical (LO) mode. According to the Raman selection rules of the WZ crystal structure only the TO mode is allowed in this polarization configuration [26], however, the LO mode may appear due to crystal stacking faults in the NW [15]. As seen in the lowermost curve of figure 1(c) the oxidized NW shows a drastically different spectrum containing two high intensity peaks at 203 and 250 cm −1 which do not match any phonon energies of the InAs structure but rather the E g (TO) mode at 198 cm −1 and A 1g (LO) mode at 257 cm −1 of crystalline arsenic [27] which can form at the surfaces of InAs as a result of the reaction As 2 O 3 +2InAs→In 2 O 3 +4As as proposed in [28].…”

“…Investigating the fundamental oxidation process of the nanowires is therefore highly relevant. To this end, locally accelerating the reaction by focused laser irradiation has been demonstrated and can be combined with micro-Raman spectroscopy to provide information about the vibrational modes of individual semiconductor nanowires [8][9][10][11] and also conveying information about the elemental composition [12,13], crystal properties [14], and defects [15] as well as free carrier densities and mobilities [16]. Also, at high intensities, focused laser irradiation has been shown to enable controlled local cutting or chemical modification of InAs and GaAs nanowires by local oxidation and formation of crystalline arsenic [17][18][19][20][21] and enables welding of metal nanowires [22].…”

Free standing modulation doped core–shell GaAs/AlGaAs hetero‐nanowires

“…As we have previously shown, the nanowires grown under such conditions are oriented perpendicular to the substrate surface [12]. They are composed of nominally undoped GaAs, with pure zinc-blende structure and a low density of twins [13,14]. The nanowires reach a total length of 9 μm and a typical diameter of 80 -100 nm after 3 hours of growth.…”