Raman Spectroscopic Determination of Electron Concentration in n-Type GaSb
James E. Maslar, Wilbur S. Hurst, C Wang
Phonon-plasmon coupled mode Raman spectra of n-type GaSb were measured at room temperature as a function of electron concentration. These spectra were obtained using an optical system based on 752.55 nm excitation. Utilization of this wavelength permits greater sensitivity to GaSb coupled mode Raman scattering over a wider doping range than is possible with visible wavelength excitation-based systems. A relatively simple spectral model for the electronic contribution to the dielectric function was evaluated for determination of electron concentration from the bulk coupled mode spectra. The electron concentrations were determined from the Raman spectra by minimizing the sum of the squared residuals between a measured and a simulated spectrum as a function of Fermi energy and a plasmon damping parameter. The electron concentrations determined from the fits to the Raman spectra were compared to the electron concentrations determined from single magnetic field Hall effect measurements that were corrected to account for carriers in two conduction band minima. The electron concentrations determined using the two methods differed from -16 percent at low doping levels to +24 percent at high doping levels. In general, compared to the electron concentrations determined from the corrected Hall effect measurements, the electron concentrations determined from the Raman spectra were lower for epilayers with lower Hall effect electron concentrations and higher for epilayers with higher Hall effect electron concentrations. The deviations between the results obtained with the two methods were attributed to the impact of uncertainties in GaSb materials properties on the accuracy of the correction to the single field Hall effect measurements and to the limitations of the spectral model employed.