Extracting Electron Densities in n-Type GaAs from Raman Spectra.

Raman measurements can be utilized as a non-destructive method for determining carrier density in compound semiconductors. Rigorous determination of carrier density involves comparing measured and simulated coupled phonon-plasmon Raman spectra. Theories of varying degrees of complexity have been employed for simulating spectra in which spectra are generated as a function of Fermi energy (or carrier density in the degenerate limit). In general, previously utilized spectral models are strictly valid only for a temperature near 0 K and either for the classical or degenerate doping limit. However, such models cannot necessarily capture all spectral information. To overcome this limitation, we have developed a model that is valid at any temperature, any doping level, and for arbitrary values of the ratio Q²/α (where Q is the magnitude of the normalized wavevector, and α is the normalized frequency used in the Raman measurements). We compare measured n-type GaAs spectra, obtained from epilayers with different carrier concentrations, with simulated spectra obtained with this new spectral model employing different descriptions of the band structure as a function of Fermi energy.