Comprehensive study of (Al)GaAs Si-doping using reflectance anisotropy spectroscopy in metal-organic vapour-phase epitaxy

The n-type doping of (Al)GaAs grown on GaAs using silicon (Si) was studied in metal-organic vapour-phase epitaxy using reflectance anisotropy spectroscopy. The reflectance anisotropy (RA) of GaAs was measured on undoped layers and on layers with increasing Si n-type doping concentrations up to 1 x 1020 cm-3. It was found that the RA still changes even though the carrier concentration stays constant and only the Si concentration in the crystal lattice is increasing at values above 5 x 1018 cm-3. The doping dependence of the RA of AlxGa1-xAs layers up to aluminium concentrations of x = 0.7 is similar to the GaAs case with an increasing amplitude while for highly doped AlAs it is slightly different. While the broad peak in the RA spectra around 3.9 eV of Si-doped GaAs and AlxGa1-xAs up to x = 0.7 shows a steady decrease with increasing doping concentration the RA of AlAs in this spectral region shows a shift of the peak towards lower photon energies and an increase in amplitude for doping concentrations above 2 x 1018 cm-3. Finally, the temperature dependence was studied for Al0.5Ga0.5As showing that the influence of the doping on the RA spectra is decreasing with increasing temperature