Autodoping of Silicon Films Grown Epitaxially on Sapphire

Doping by the substrate of silicon films grown epitaxially on sapphire has been measured. Spectroscopic analysis of the silicon films has shown that aluminum is the major impurity. In films grown with further processing below 1200°C introduces no additional doping from the substrate. The doping of the films by the sapphire becomes significant above 1250°C with the sapphire acting as a source of aluminum. The total number of aluminum atoms entering the silicon films is of the order of 1–2.10 15 resulting in a concentration of 2.10 18 /cc in the silicon film. The mechanism responsible for the liberation of the aluminum from the sapphire has not been determined. A qualitative description of the changes in crystal structure on heat‐treatment is given.