Raman scattering study of lattice disorder in 1-MeV Si-implanted GaAs

Abstract

We have used Raman scattering to study the lattice disorder created by the implantation of 1-MeV Si ions into GaAs. Using the change in the longitudinal optical (LO) phonon-line position as the signature for lattice damage, combined with chemical etching for controlled layer removal, we monitored the evolution of the disorder depth profile as a function of implantation dose. The shape of the depth profile of the disorder agrees with the theoretical simulation TRIM for doses of 1 X 10 14 cm-2 or lower. For higher doses a saturation is observed in the amount of residual disorder. This saturation is a manifestation of dynamic annealing occurring during the high-energy implantations, which we attribute to enhanced defect mobility, induced by the transfer of energy to the lattice, in atomic collision cascade processes. In order to correlate the spectral features in the Raman spectra with structural changes in the ion-implanted samples, we characterized the implantation-induced lattice damage using ionchanneling and transmission electron microscopy (TEM) measurements. The residual defects in the MeV -implanted samples are found to consist of dislocation loops and discrete point defects dispersed in an otherwise perfect (although probably strained) crystalline lattice. An average distance between defects was estimated from the channeling and TEM studies, and compared with the coherence-length parameter L used in the "spatial correlation model," which is commonly used to interpret quantitatively the Raman spectra of ion-implanted materials. Although the model gives a good fit to our data in terms of the position and linewidth. of the LO phonon peak, no clear correlation could be established between L and the interdefect separations. We also observed the appearance of the broadbands at about 70, 180, and 245 cm--1, in the Raman spectra, which are commonly attributed to amorphous GaAs, although no trace of amorphous material was detected by the TEM analysis. Our results indicate that the quantitative interpretation of Raman spectra to determine crystalline properties of ion-implanted materials, as wen as the assignment of Raman spectral features to particular defect structures, is not unambiguously established yet.

Characterization of GaAs wire crystals grown on porous silicon by Raman scattering

“…The total shift of about 9 cm Ϫ1 in comparison to crystalline GaAs is the largest so far observed, since implanted c-GaAs readily turns into a-GaAs after reaching a shift of 5-6 cm Ϫ1 in the LO band. 5,6,9,10 Another observation drawn from Figs. 3͑a͒ and 3͑b͒ is that the total intensity of the spectra excited with the 581 nm radiation is about a factor of 5 times larger than that excited with the 514 nm radiation.…”

“…Although the size of the GaAs cylinders is in the nanometer scale, it is not small enough to produce a downshift and broadening of the Raman modes due to phonon confinement within the crystallites of GaAs. 5 Nevertheless, when there is a high concentration of point defects, the mean distance between them can be small enough to significantly reduce the coherence length of phonons. 6 This mechanism relaxes the momentum selection rule for Raman scattering, letting phonons with q 0 become observable.…”

Structural and electronic effects of argon sputtering and reactive ion etching on In0.53Ga0.47As and In0.52Al0.48As studied by inelastic light scattering

“…20,21 The broadening of the LO phonon is a result of the lowering of the crystal symmetry leading to contributions to the scattering from non-zone-center optical phonons. 17 Two LO-phonon modes are observed for In 0.53 Ga 0.47 As ͑Ref.…”

“…18͒, and In 0.52 Al 0.48 As ͑Ref. 21 Another probe of structural modification is violation of the first-order qϭ0 selection rule in the form of dipole-forbidden LO-phonon scattering. These modes can be used to probe structural modification, because a broadening, shift in frequency, or decrease in intensity of the dipole-allowed LOphonon mode can result from the creation of various densities, types, and spatial distributions of defects in the lattice.…”

Micro-Raman Characterization of Unusual Defect Structure in Arsenic-Implanted Silicon

“…Raman spectroscopy is useful for characterizing the chemical bonding and crystal structure of solids because Raman scattering depends not only on the atomic masses and bond force constants, but also on the polarization and direction of the incident light, the crystal symmetry, and the orientation of the sample. Consequently, it has often been used to study the damage to semiconductors induced by ion implantation [1][2][3][4]. The Raman selection rules, which for crystalline materials restrict spectroscopic activity to the Brillouin zone center, break down as lattice order is broken.…”