Non-stoichiometry in (001) low temperature GaAs by Raman spectroscopy

Using the optical phonons as an internal probe, the change in the dielectric permittivity has been analysed by Raman scattering in GaAs grown by MBE at low temperature (LT-GaAs). The screening effect is discussed in terms of a solid solution whereas the strain one is treated in the perfect adhesion hypothesis. Experimentally, the strain and the screening effects have been discriminated by using various scattering geometries. As the LT-layers with large non-stoichiometry have a poor thermal conductivity, it is shown that local heating considerably affects the experimental data. This can be avoided by surface convective exchange then leading to perfect agreement between the recorded phonon frequency shift and the expected ones. As a consequence, this sustains a new method for a quantitative determination of the As excess in LT-layers.