THYRISTORS CREATED FROM HIGH PURITY FLOAT-ZONE SILICON FOR OPERATION AT GREATER THAN 5000 VOLTS

RECTIFIERS THAT CAN BLOCK 20 KV AND THYRISTORS THAT CAN BLOCK 10KV ARE NOT PRESENTLY AVAILABLE. SILICON SUBSTRATES FOR DEVICES WITH THIS CAPABILITY MUST BE OF EXTREMELY HIGH PURITY; THE RADIAL RESISTIVITY GRADIENT MUST BE UNIFORM TO WITHIN ONE OR TWO PERCENT AND FREE CARRIER GENERATION DUE TOTEMPERATURE MUST BE SUPPRESSED. THIS PROJECT ADDRESSES ALL THESE REQUIREMENTS. SINGLE CRYSTAL P-TYPE SILICON WITH RESISTIVITY OF 20,000 OHM-CM CAN BE PRODUCED. THIS SINGLE CRYSTAL SILICON WILL BE NEUTRON TRANSMUTATION DOPED AT THE UNIVERSITY OF MICHIGAN NUCLEAR REACTOR TO PRODUCE 500 OHM-CM N-TYPE SILICON WITH ONE OR TWO PERCENT RADIAL GRADIENT. THE UNIFORM RESISTIVITY RADIAL GRADIENT IS NECESSARY TO PREVENT DEVELOPMENT OF HOT SPOTS ON THE THYRISTOR THROUGH WHICH THE CURRENT WILL FLOW. MELT-DOWN OFTHE DEVICE WOULD RESULT IF HOT SPOTS WERE PRESENT. THE DEVICE DESIGN WILL ACCOMMODATE LOW TEMPERATURE (E.G., 77 K) OPERATION. AT THIS LOW TEMPERATURE, FREE CARRIER GENERATIONCAUSED BY HEAT WILL BE GREATLY DIMINISHED. THE IMPORTANT DESIGN CHARACTERISTICS WILL BE HIGH VOLTAGE BREAKDOWN AND TEMPERATURE STABILITY. THE OPERATING PARAMATERS WILL BE DEFINED IN THE TEMPERATURE RANGE 77-400 K.