A novel method was proposed for the improvement of the uniformity of EL2 distributions in liquid-encapsulated vertical Bridgman material. This so-called growth-furnace annealing method involved the control of the thermal history of the crystal by using various procedures. Firstly, the crystal was maintained at temperatures above 1100C during growth in order to prevent any excess As which was incorporated into the crystal from precipitating at dislocations and producing a non-uniform distribution of interstitials which could be a source of EL2. When growth was finished, the crystal was cooled to room temperature via annealing in order to generate EL2. This was done while maintaining the temperature distribution uniform over the entire crystal. These procedures made it possible to impart an identical annealing treatment to the whole crystal as well as generating EL2 within a uniform concentration of As interstitials. This resulted in a uniform distribution of EL2 throughout the whole crystal. It was demonstrated that the resultant microscopic uniformity of EL2 was superior to that which was obtained by using so-called post-growth annealing.

H.Nakanishi, H.Kohda: Journal of Crystal Growth, 1995, 155[3-4], 171-8