Process for the formation of single crystals from the gas phase

Claim 1

In a process for the formation of single crystals from the gas phase wherein source gases are formed in a vessel from solid starting materials and the source gases are conducted to a walled growth chamber provided for the formation of a single crystal, said chamber being heated to a temperature to maintain said source gases in the gaseous phase and wherein the single crystal which is growing on a surface within said growth chamber is exposed to a static temperature gradient between the exposed crystal surface and the surroundings within the growth chamber, wherein the improvement comprises: heating the walls of the growth chamber to a temperature required to maintain said source gases in a gaseous phase until the formation of nuclei of the single crystal is accomplished on a cooled growth surface in the growth chamber, and subsequent to the formation of the nuclei, cooling the walls of the growth chamber to provide a temperature gradient effective to cause the entire exposed surface of the crystal to be warmer than its surroundings, said exposed surface being within the metastable range of supersaturation.