Ellipsometric study of metal-organic chemically vapor deposited III–V semiconductor structures

Metal-organic chemical vapor deposition was used to grow epitaxial layers of AlGaAs, GaAs and InGaAs on semi-insulating GaAs substrates. The ternary composition of the thick layers was determined by double-crystal X-ray diffraction (DCXRD). Variable angle spectroscopic ellipsometry was used to characterize several types of structures including relaxed single-component thick films and strained lattice multilayer structures. The thick film characterization included ternary alloy composition as determined by a numerical algorithm and interface quality. The results for the alloy composition were equal to the DCXRD results, to within the experimental errors except for the top layer of a thick AlGaAs film. The strained layer multistructures were analyzed for all layer thicknesses and alloy compositions. For most layers, the thickness was equal to the nominal values, to within the experimental errors. However, in all three In_0.3Ga_0.7As samples, the indium concentration estimated from the relaxed layer's InGaAs algorithm was around 21%, i.e. much lower than the nominal value. This result indicates a shift in the critical points of the dielectric function, owing to strain effects.