Study of InAs nanowire structure using spatially resolved Raman spectroscopy

The structure of tapered InAs nanowire (diameter ∼ 400 to 200 nm from base to tip) along the length (10 µm) is studied using spatially resolved Raman spectroscopy. The observed Raman spectra suggest presence of both wurtzite (WZ) and zincblende (ZB) structure for InAs with increasing content of wurtzite structure towards tip. Polarized Raman measurements shows dominance of E2h (WZ) ∼ 213 cm−1 in x(y, y)x and dominance of TO (ZB) ∼ 215.5 cm−1 x(z, z)x configuration for light polarization perpendicular and parallel to nanowire axis, respectively. The blue and red shift in WZ and ZB phonons (base and center) from their bulk value is attributed to changed near neighbor interaction due to presence of the other structure. However, the blue shift of both E2h (WZ) and TO (ZB) near tip is indicative of additional mechanical compressive stress.