A NEW ELLIPSOMETRIC MODEL OF WET AND DRY-ETCHED GAAS-SURFACES

In this paper we describe the application of ellipsometry to study (100)GaAs surfaces. Investigations concern the surfaces after polishing, cleaning, wet and dry etching of GaAs substrates and the surfaces of liquid phase epitaxy- and molecular beam epitaxy-grown GaAs epilayers. A new model is proposed to interpret the ellipsometric data. It assumes the presence of a transitional layer characterized by spherical disturbances situated between the bulk GaAs and the native oxide layer: The ellipsometric parameters are analysed as a function of the size and density of the spherical disturbances and the transitional and native oxide layers. Different angles (70:75 degrees) of the incident light beam are used at a wavelength of 546.1 nm. A refractive index of 1.81 for the oxide film and (4.05 - i0.304) for the GaAs substrate an assumed. Our results show that the thickness of the native oxide layer changes from 11 Angstrom to 35 Angstrom depending on the surface treatment. The thickness of the transitional layer reaches the radius of the spherical disturbances. Their radius ranges from 10 Angstrom to 30 Angstrom, while the complex refractive index changes from (4.05 - i0.34) to (4.70 - i1.30).