Structural characterization of GaAs and InAs nanowires by means of Raman spectroscopy

Abstract

We report Raman studies of GaAs and InAs nanowires (NWs) grown on SiO2 and GaAs surfaces by means of catalyst-assisted molecular beam epitaxy. We have investigated several tens of NWs grown using either Mn or Au as a catalyst. The LO and TO phonon lines of the NWs showed an energy downshift and a broadening as compared to the lines usually observed in the corresponding bulk materials. A doublet is sometimes observed in the LO region due to the observation of a signal attributed to the surface optical (SO) phonon. The energy position of the SO phonon agrees with the values expected considering the section diameter of the NWs. LO and TO downshifts are due to the presence of structural defects within the NWs. The larger the energy downshift, the smaller the dimension of the defect-free regions. The results demonstrate that different catalysts provide wires with comparable crystal quality. The measurements also point out that differences in defect density can be found in wires coming from the same batch indicating that a substantial effort will be needed to obtain high homogeneities of the NW quality.

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

“…The GaSb peak intensity scales to the anticipated thickness of the GaAsSb layers in the NWs. The high-intensity ratio of TO to LO phonon modes of GaAs has been commonly observed in GaAs NWs, being the highest for N1 and is attributed [45] to the LO mode being forbidden from certain surface facets as opposed to no such restrictions imposed on the TO phonon modes. A relatively low TO/LO GaAs phonon peak ratio as well as a lower FWHM of these two in NW N2 is also indicative of better quality layers consistent with the PL data discussed earlier ( Figure 3.11).…”

Phonon Confinement Effect in III-V Nanowires

“…Micro-Raman spectroscopy is particularly well suited to study the III-V semiconductor NWs, because it gives good signal of the 1 st order Raman spectra for both LO and TO phonons of III-V semiconductor material. Figure 3 illustrate this fact, where the representative Raman spectra of (a) GaAs NWs and (b) InAs NWs grown with two different catalysts, Au-catalyzed NWs (top spectrum), Mn-catalyzed NWs (middle spectrum) and GaAs epilayers or InAs bulk (bottom-most spectrum) are shown [20]. Raman spectra shown in Figure 3 are for the NWs grown on SiO 2 substrate.…”

“…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.…”

Generic technique to grow III-V semiconductor nanowires in a closed glass vessel

“…The peaks appear at 216 cm −1 and 233 cm −1 and correspond to the LO and TO modes of InAs. [27][28][29] As we mentioned before, our experimental setup for the growth of InAs nanowires in a closed glass tube vessel is totally different from previous experiments. Including the pressure, atmosphere, and growth temperature, precise control of almost all growth conditions is not needed in our technique.…”