Micro-Raman study of photoexcited plasma in GaAs bevelled structures

The properties of the photoexcited plasma in n-GaAs and its influence on micro-Raman spectra were studied on bevelled structures. The modes of the photoexcited free-carriers plasmon–LO–phonon (PLP) coupling have been detected in the surface depletion layer at room temperature in continuum wave (CW) mode. The strong modifications of the intensities of TO–phonon and LO–phonon modes were observed along the bevel. They were discussed in terms of scattering by PLP coupling. The dependence of the ratio of the intensities of TO–phonons and LO–phonons was linear along the bevel in the region of the surface depletion layer. The first derivative of this dependence is a characteristic value for the corresponding doping concentration. Five Si-doped GaAs layers with different doping levels were analyzed in this way to obtain a calibration function for determining the doping concentration profile in the very thin GaAs layers.