RAMAN SPECTROSCOPIC STUDIES OF ION-IMPLANTED GALLIUM-ARSENIDE AND INDIUM-PHOSPHIDE (OPTICAL, III-V, SEMICONDUCTOR)

The Raman spectra of GaAs and InP implanted with Be and Si ions with fluence ranging from 5 x 10('12) to 1 x 10('16) ions/cm('2) were investigated. One important feature of the ion-implanted samples is that the lattice disorder can be increased in a controlled fashion by the gradual increase of implantation dose. It is studied in this work how this gradual transformation from a single crystal to an amorphous phase is reflected in the Raman spectra.;As the amount of implantation dose is increased further to a value of 1 x 10('15) ions/cm('2), the Raman spectra exhibit many additional low frequency features, due to the relaxation of Raman selection rules. These results are interpreted in terms of disorder induced first order Raman spectra (DIRS), arising from phonons with non-zero wave vectors. It is found that at this fluence level, the system is still in a partially disordered state, i.e., it has not yet been transformed into the amorphous phase. The defect concentration is sufficient so that the relaxation of selection rules becomes observable but the crystalline phonon dispersion relations are still preserved. In this case, the reduced Raman spectra (RRS) give a measure of the crystalline one phonon density of states.;Upon further increase of the implantation dose to a typical value of 1 x 10('16) ions/cm('2), the Raman spectra exhibit a washed out and broad band spectral feature containing only two peaks, one corresponding to the optical phonons and other to the acoustical phonons. This is an indication that the sample has been transformed into an amorphous phase where the meaning of unit cell and Brillouin zone is lost and the Raman spectra represent the amorphous phonon density of states. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI.;It is observed that when the implanted fluence is less than 5 x 10('12) ions/cm('2), the vibrational spectra of the materials are insensitive to the small damage concentration. When the number of defects introduced in the crystal is increased corresponding to a typical fluence level of 5 x 10('13) - 5 x 10('14) ions/cm('2), they begin to perturb slightly the crystalline phonon density of states. This has resulted in introducing broadening in the crystalline lattice modes, due to the disorder enhanced decaying channels. Also a marked difference in the behaviour of the LO and TO modes with respect to broadening with fluence is observed. These results are interpreted using a frequency dependent anharmonic damping constant.