Patent ID: 7255740

Claim:
A method for making a low-stress or stress-poor single crystal with a hexagonal crystal structure, which has a crystallographic c-axis perpendicular to a [0001] surface, from a melt of a crystal raw material, said method comprising the steps of: a) dipping a single crystal in said melt so that a solid-liquid phase boundary is formed while keeping the single crystal at a temperature below a melting point of the crystal raw material; b) withdrawing said single crystal from the melt by drawing upward with an upwardly directed drawing motion along the crystallographic c-axis so that a temperature gradient of at least 30 K/cm is present in the single crystal within 1 cm of the solid-liquid phase boundary in order to grow the single crystal with the hexagonal crystal structure with the crystallographic c-axis; and then c) subjecting the single crystal produced in step b) to a tempering treatment.