Spatially resolved Raman spectroscopy study of uniform and tapered InAs micro‐nano wires: correlation of strain and polytypism

Abstract

The asymmetric peak ~212–218 cm−1 occurring in InAs micro‐nanowires (MNWs: diameter: 2 μm – 400 nm) is investigated using spatially resolved Raman spectroscopy of uniform, bent and long tapered MNWs grown on a Si (001) substrate. It is attributed to superposition of E2h phonon (wurtzite: WZ) and TO phonon (zinc blende: ZB) of InAs. Polarized and wavelength‐dependent spatially resolved Raman spectroscopy establishes the presence of WZ and ZB phases in these MNWs. However, formation of WZ phase for larger diameter InAs MNWs is not commensurate with existing growth mapping studies. Further, study of these MNWs suggests that the fraction of WZ to ZB content in a MNW depends not only on the diameter but also seems to be governed by local growth seeding/conditions. This in turn leads to either tapered or uniform MNW growth under the same (external) growth conditions. The variation of these wavenumbers that of bulk value is correlated to the residual stress present in ZB and WZ phases due to the presence of the other (WZ/ZB) phase. Consistently, temperature‐dependent Raman data show that there is a measurable contribution of stress to dω/dT, a positive for ZB and negative for WZ phonons, due to differences in their thermal expansions. Further, effective thermal expansion coefficient of WZ InAs in the presence of ZB phase is calculated to vary in the range 10–19 × 10−6/K from base to tip of a MNW at ~80 K, which is not possible to determine otherwise. Copyright © 2017 John Wiley & Sons, Ltd.