SiGe heteroepitaxial structures evaporated in ultra-high vacuum

Polycrystallinity, cracking, fragment boundaries, mechanical stress, dislocations and stacking faults were investigated in epitaxial SiGe structures of abrupt junction, prepared by UHV evaporation. The structural properties were studied as a function of the condensation temperature, the thickness of the grown layer and the cooling rate. The methods used were: microscopic and Laue patterns, surface reflection X-ray topographical studies, and radius of curvature measurements. It was found that from the point of view of the cracking the condensation temperature plays hardly any role between 880 ° and 500 °C, nor does the layer thickness between 2 and 20 micro m; it is the thermal expansion effect which is decisive. Under our experimental conditions, in samples cooled down from the condensation temperature to 300 °C at a rate not greater than 10 °C/min the cracking effect decreased to a minimal value. The true stress of SiGe structures grown and cooled under suitably chosen conditions was found to be about 1.5 × 10⁹ dyn/cm² and was independent of the preparation conditions. The polycrystallinity of the Ge layers was affected by the condensation temperature and by the surface purity of the Si single-crystal substrate.