Micro-Raman-scattering study of surface-related phonon modes in porous GaP

Abstract

Porous GaP layers prepared by electrochemical dissolution of ͑100͒-oriented bulk material have been studied by micro-Raman spectroscopy. The anodization causes a breakdown of the polarization selection rules, inherent to a ͑100͒ surface, accompanied by a downward shift of the LO-phonon frequency and by the appearance of a surface-related vibrational mode in the gap between the bulk optical phonons. The frequency of the surface-related mode was found to decrease from 398 to 394.3 cm Ϫ1 with increasing anodization current. A Raman line-shape analysis based on the light scattering due to the electro-optic and deformation potential mechanisms is presented. ͓S0163-1829͑97͒03312-2͔

Effect of temperature and micro-morphology on the Ag Raman peak in nanocrystalline CuO thin films

“…We must exclude the possibility that this spatial variation is caused by material inhomogeneities that affect the local phonon modes, as we observe no variation in Raman spectra at the lower laser power. In addition, such material inhomogeneities (e.g., impurities, 42 defects, 43 phonon confinement, 44,45 surfacemodes 46 ) would all be expected to give rise to an asymmetric Raman peak, which we do not observe. Similarly, homogeneous stress (beneath the probe laser) should be expected to lead to shifts in x peak that are uncorrelated 2 with C. Again, this is not consistent with our observations.…”

Raman scattering of nanoporous semiconductors

“…However, two modes were observed and attributed to the F-T and F-L Fröhlich modes in Raman measurements of por-GaP with a honeycomblike morphology under pressure up to 10 GPa and at T D 5 K. 92 A surface-related phonon mode in porous GaP at 397 cm 1 was first observed by Tiginyanu et al 93 and interpreted in terms of a Fröhlich mode on the basis of an effective medium approach. 94 It was shown that its wavenumber decreases with increasing anodization current. The fabrication of freestanding porous membranes, detached from the substrate, 95 enabled the investigation of the surface modes in porous membranes filled with liquids 96 and infrared reflectance measurements.…”

Raman Scattering in GaN Nanocolumns and GaN/AlN Multiple Quantum Disk Nanocolumns

“…It was pointed out in porous GaP, which can be regarded as a system of interpolated columnlike pores in GaP, that the frequency of the Fröhlich mode depends strongly on the relative concentration of GaP in the air. [7] Tiginyanu et al [6] observed it in a sample of GaN columnar nanostructures, which was fabricated by electrochemical dissolution of bulk material. They estimated the average concentration c 0 , taking into account a Gaussian distribution and using the effective dielectric constant.…”