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Measurements of reflectivity and Hall effect have been made on polycrystalline n-type samples of GaAs and alloys of the systems GaAs xSb1-x and Ga1-xAlxAs to find values of electron effective mass at the bottom of the conduction band m*00/m . The experimental data were obtained with a Baird monochromator which was modified to give double beam operation and extended wavelength range up to 30 mum, so that measurements of the free carrier reflectivity could be made on samples with low carrier concentration. The reflection coefficient R and hence the index of refraction eta were obtained from the experimental measurements. The variation of eta2 was plotted as a function of the square of the wavelength. For each sample, the graphical result (eta 2 vs lambda2) was found to be a straight line and it was extrapolated to zero wavelength to obtain the optical dielectric constant epsilon infinity. The slope of the line also was determined and used to obtain the value of effective mass at the bottom of the conduction band. For the systems GaAsxSb1-x the alloy compositions were determined by the X-ray powder photograph method. For the two alloy systems GaAsxSb1-x and Ga 1-xAlxAs, optical dielectric constant and effective mass values were measured from infrared reflectivity for the first time. The values of the effective masses were determined by the simultaneous solution of the integrals giving the statistical carrier concentration and the slope of the free carrier reflectivity under the condition of the general degeneracy, the lattice contribution to the slope being taken into account. Theoretical values of the effective masses in the (000) conduction band as a function of alloy composition were calculated for the alloy system GaAs xSb1-x using the disorder equation (73W) and Kane equation (57K) for the effective masses. The experimental results were found to be in better agreement with the disorder equation of the effective mass than with the Kane equation. Finally, to complete the outline of the project, it should be mentioned that the values of optical Fermi energy, dielectric constant, optical relaxation time, optical mobility and optical conductivity were calculated for 12 samples of the alloys GaAsxSb1-x and Ga1-xAl xAs.

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