  The asymmetric peak at 212 - 218 cm-1 occurring in InAs micro-nano wires is
investigated using spatially resolved Raman spectroscopy (SRRS) 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 SRRS 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, which needs
to be understood further. Study of several of these MNWs suggest that the
fraction of WZ to ZB in a MNW is decided not only by diameter, but also by
local growth seeding/conditions leading to either tapered or uniform MNWs
formation, although, external growth conditions are same. Variation of these
frequencies that from bulk value are correlated to residual stress generated in
ZB and WZ phases due to presence of WZ and ZB phases, respectively.
Consistently, temperature dependent Raman data shows that there is a measurable
contribution of stress to dw/dT, a positive for ZB and negative for WZ phonons,
due to difference in their thermal expansions. Further, effective thermal
expansion coefficient of WZ InAs in presence of ZB phase is calculated to vary
in the range 10 - 19 x 10-6/K from base to tip of a MNW at 80 K, which is not
possible to determine otherwise.
