R. Aggarwal

Time evolution studies of laser induced chemical changes in InAs nanowire using Raman spectroscopy

We report the study of time evolution of chemical changes on the surface of an InAs nanowire (NW) on laser irradiation in different power density regime, using Raman spectroscopy for a time span of 8–16 min. Mixture of metastable oxides like InAsO4, As2O3 are formed upon oxidation, which are reflected as sharp Raman peaks at ∼240–254 and 180–200 cm−1. Evidence of removal of arsenic layer by layer is also observed at higher power density. Position controlled laser induced chemical modification on a nanometer scale, without changing the core of the NW, can be useful for NW based device fabrication.

Intersubband plasmon-phonon coupling in GaAsP/AlGaAs near surface quantum well

The investigation of electron-phonon coupling in near surface GaAs1−xPx/AlyGa1−yAs quantum well structures using wavelength and intensity dependent Raman spectroscopy shows that in the near surface quantum well case, coupled modes are situated at the frequency between longitudinal optical (LO) and transverse optical phonons of GaAsP, which is forbidden for the coupled electron-phonon modes in the bulk ternary alloy. The observed “GaAs like” and “GaP like” LO phonon-intersubband plasmon coupled mode frequencies decrease with increase in carrier density. These results corroborate well with the theoretical calculation for variation of two dimensional electron gas-phonon coupling with carrier density in ternary alloys.

Intersubband Plasmon ‐ Phonon Coupling in GaAsP/AlGaAs Single Quantum Well: A Raman Spectroscopy Study

A Raman scattering study of GaAs1−yPy (y = 0.14)/AlxGa1−xAs (x = 0.7) single quantum wells has shown two mode behavior for both barrier and quantum well alloys. In this report we present investigation of origin of an additional mode ∼284 cm−1. From wavelength and intensity dependent Raman measurements, it was concluded that the mode is intersubband plasmom‐phonon coupled mode due to photoexcited carriers. The coupled mode frequency dependence on free carrier density as predicted by theory is qualitatively in agreement with observed coupled mode frequencies in intensity dependent Raman measurements.

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.