Asymmetrical thyristor with highly doped anode base layer region for optimized blocking and forward voltages

Claim 1

An asymmetrical thyristor comprising: at least four zones of alternately opposite conductivity type including a relatively high doped outer P emitter zone, a relatively lightly doped N base zone, a relatively lightly doped P base zone and a relatively highly doped N emitter zone layered one on top of the other, said P emitter and N emitter zones contacting respective main electrodes, and said N emitter zone having a recess through which said P base zone extends to contact a control electrode; said N base zone having a partial region adjacent the P emitter zone, said partial region having a doping concentration (C) which is higher than that of remaining regions in the N base zone and which decreases from a higher value (C max ) to a lower value (C min ) in a direction towards the P emitter zone perpendicular to the four zones; wherein with a predetermined maximum forward blocking voltage applied to the main electrodes there is formed a blocking layer in said N base zone and a neutral zone W n extending from the edge of the blocking layer in the N base zone into the P emitter zone to a location X 4 where the doping concentration of the P emitter zone reaches 1·X10 18 cm -3 ; said doping concentration (C) having the value C min at a location X 3 which is at least 30 percent of the width of the neutral zone W n away from the edge of the blocking layer; and the width of the neutral zone (W n ) being in the range between 1·10 -3 cm and 8·10 -3 cm and having a value which is calculated in accordance with ##EQU3## wherein τ R refers to the mean recombination life span of the minority charge carriers in the partial region, τ G refers to the mean generation life span of the minority charge carriers in the blocking layer having a width W S and F is defined by ##EQU4## which is the integral across the doping concentration (C) from the edge of the blocking layer in the inner N doped zone at X 2 to the location X 3 at which the doping concentration (C) reaches the value C min in the partial region and which is standardized to the integral across a constant doping concentration on the level of C max between the same limits.