Figure 1

(a) X-ray diffraction scan of a selected InAs nanowire array sample, confirming the epitaxial relationship between InAs(111) and Si(111) substrate. (b) High-resolution diffraction profile in the vicinity of the main InAs diffraction peak, evidencing an elongated reflection due to slightly different atomic distances within the layered stacking of InAs. An electron diffraction pattern of a single wire is shown in (c). All reflections in the diffraction pattern can be indexed according to a wurtzite structure in [10-10] zone axis. The diffuse streaks along the growth direction indicate stacking disorder. A HRTEM image of the same wire in the same orientation is shown in (d). In addition to regions with WZ structure and regions with disordered stacking, a small domain with ZB structure is also visible. (e) Approximated phonon dispersion in InAs wurtzite [0001] (dotted lines) obtained by backfolding the InAs zincblende phonon dispersion along [111] (solid lines). Additional zone center modes appear in the WZ structure. The ZB dispersion is taken from Ref. 30.Reuse & Permissions

Figure 2

(a) Illustration of the scattering geometry for Raman measurements on transferred InAs nanowires. The Cartesian coordinate system is chosen according to the nanowire crystal directions and geometry, with ${\mathbf{z}}^{\prime }$ and ${\mathbf{y}}^{\prime }$ parallel and perpendicular to the nanowire axis, respectively. Incident and scattered light polarizations ${\mathbf{e}}_{\mathbf{i}}$ and ${\mathbf{e}}_{\mathbf{s}}$ lie in the plane perpendicular to the backscattering direction ${\mathbf{x}}^{\prime }$. (b) Representative Raman spectra of bulk InAs and a single InAs nanowire. The TO peak of the InAs nanowire is found at significantly lower Raman shift, whereas the LO coincides well with the bulk value.Reuse & Permissions

Figure 3

Raman spectra of a InAs NW of 150 nm diameter for the two main polarized scattering configurations collected with (a) 514.5 nm and (b) 647.1 nm excitation wavelength. The peak in (b) labeled with an asterisk is a plasma line of the Kr${}^{+}$ laser.Reuse & Permissions

Figure 4

(a)–(d) Representative, polarization-dependent Raman spectra (gray squares) of a 150-nm-thick InAs nanowire. The decomposition into individual Lorentzian contributions is given by the solid lines. (e) Histogram of peak frequencies obtained from Lorentzian fits as in (a)–(d) for the four scattering geometries and for measurements on several positions on six individual nanowires. Four clearly separated peaks arise.Reuse & Permissions

Figure 5

(a)–(d) Azimuthal dependence of the Raman scattering intensity for the four individual peaks observable for the InAs nanowires. (e)–(h) Polar behavior calculated by wurtzite-type Raman tensors with appropriate symmetry and parameters.Reuse & Permissions