Methodological and instrumental problems in high-precision in situ ellipsometry diagnostics of the mercury cadmium telluride layer composition in molecular beam epitaxy

Problems of high-precision in situ ellipsometry diagnostics of the composition of a mercury cadmium telluride (MCT) solid solution in the process of its growth using the molecular beam epitaxy are considered. The required precision was estimated for ellipsometry measurements aimed at determining the MCT composition with a permissible dispersion of ±0.003 mole fraction of CdTe. It has been revealed that for ellipsometers based on the static photometric scheme the instability of measurements is mainly caused by a random change in the directivity of the laser radiation. In combination with polarization nonuniformity over the area of the optical-section elements, this results in continuous drift of measured ellipsometric parameters. Based on these investigations, a high-stability laser ellipsometer has been designed. When used to monitor the in situ MCT layer growth by the molecular beam epitaxy, it allowed a decrease in the dispersion of the MCT composition by an order of magnitude from experiment to experiment and its precision to be maintained at a level of ±0.003 mole fractions of CdTe.