Experience with Neutron Transmutation Doped Silicon in the Production of High Power Thyristors

Abstract

High power thyristors have been processed, using NTD silicon ingots preannealed at 800°C and 1,200°C. Annealing at these temperatures produces different lifetime distributions as measured before processing into thyristors using a light-spot method and liquid rectifying contacts. The material annealed at 1,200°C shows lifetime variations which reflect the spiral patterns arising during the growth of the crystal. These lifetime variations were not eliminated by the processing but remained in fully-processed thyristors. The effect of these lifetime variations was to increase the leakage current in the thyristors at temperatures above room temperature. A deep level possibly responsible for this effect was detected by the DLTS method. Some methods are described which were found to be successful in diminishing these lifetime variations. Material annealed at 800°C did not exhibit these lifetime variations.