Anharmonic effects on Raman scattering of Longitudinal Optical (LO) phonon of gallium phosphide

The disturbance of periodic array in crystal changes the frequency spectrum of host crystal. This study has been based on cubic and quartic anharmonic terms beyond the potential energy expansion of crystal. This results in a phonon-phonon interaction. This gives the anharmonic mode. In high temperature limit, an electron interacts with cubic and quartic anharmonic fields. The propagation of electron in this type of system has been produced the combination and difference bands alongwith exciton and polaron formation. The theory has been developed on the basis of many body system by taking electron Green`s function into consideration. Gallium phosphide is zincblende type structure. It has two different atoms in primitive unit cell. The response function has been established from an electron Green`s function responsible for electron phonon linewidth and electron phonon shift. These are contributed by electron-harmonic phonon part, electron-electron part, electron-localized part, electron-cubic anharmonic part, and electron -quartic anharmonic part. At high temperature, linewidth and shift have been found identical with Balkanski et al. model at high temperature. An equation of motion technique of quantum dynamics and Dyson equation approach have been applied for the analysis of Raman spectra of longitudinal optical phonon of bulk gallium phosphide. The Raman intensity obtained from this approach has been compared with the previous workers.