Standards for space charge characterization techniques

The mirror method and cathodoluminescence (CL) experiments have been used to analyse the charge trapping abilities of sapphires from two manufacturers, Rubis RSA and PI-KEM, annealed at 1000°C, 1500°C and 1700°C. The results suggest that the charging of samples annealed at 1000°C is due to defects (mainly dislocations) induced by machining and polishing, and that trap annihilations of samples annealed at 1500°C and 1700°C stem from the “selective migrations” of impurities and point defects to the available sinks, i.e. native dislocations and surfaces. The behaviour of the CL spectra at high annealing temperature confirms that the trapping ability is closely linked to material restructuring and defect evolutions. The analysis of the results reveals that the SEM mirror method in conjunction with CL can differentiate the charge trapping characteristics of sapphires from different origins. Therefore, it is felt that the two methods provide a framework for setting up standards applicable to space charge characterization and breakdown