Electron-phonon interactions in n-type In0.53Ga0.47As and In0.52Al0.48As studied by inelastic light scattering.

Abstract

Room-temperature Raman spectroscopy was used to characterize n-type-doped ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As and ${\mathrm{In}}_{0.52}$${\mathrm{Al}}_{0.48}$As layers by observing coupled longitudinal-optical (LO) -phonon-plasmon mode spectra as a function of carrier density. Carrier densities determined from the high-frequency ${\mathit{L}}_{+}$ coupled mode shift in the Raman spectra were compared to carrier densities determined from electrochemical capacitance-voltage profiling measurements. In ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As with carrier densities n\ensuremath{\le}8\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ accurate determination of carrier densities from the Raman spectra was hindered by Landau damping and small ${\mathit{L}}_{+}$ mode dispersion. Better agreement between the two techniques was observed in ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As and ${\mathrm{In}}_{0.52}$${\mathrm{Al}}_{0.48}$As for carrier densities of about 8\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ and higher, doping levels at which Landau damping is less pronounced. Surface band bending was evaluated from changes in Raman intensity as a function of carrier density of dipole-allowed LO-phonon modes originating in the surface space-charge region. Values for the surface built-in potential determined from the Raman spectra were found to be smaller than those obtained from electrical measurements. The discrepancy is attributed to screening of the surface dipole by photogenerated carriers.