Abstract:
In turn-off semiconductor components such as GTO thyristors, the semiconductor body can be locally overheated and destroyed as a consequence of inhomogeneities. The anode-side emitter is therefore doped with additional substances that locally compensate the emitter doping above the operating temperature and locally reduce the current amplification factor of the anode-side transistor structure. An increased turn-off current is thus achieved.

Description:
BACKGROUND OF THE INVENTION 
     The invention is directed to a turn-off semiconductor component having a semiconductor body with at least one first emitter zone of first conductivity type, at least one base zone of second conductivity type adjacent to the first emitter zone, an inner zone of the first conductivity type adjacent to the base zone, and at least one second emitter zone of the second conductivity type adjacent to the inner zone and that has a given doping concentration of first substances. 
     When turning semiconductor components of the recited type off, such as, for example, GTO thyristors or IGBTs, regions having increased current density, what are referred to as current lines or filaments, can occur due to inhomogeneities. When the current density becomes extremely high, the semiconductor body can be destroyed by overheating. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to improve a turn-off semiconductor component of said type such that the inhomogeneities present in the semiconductor body do not cause any locally significantly increased current density upon turn-off. 
     This object is achieved in that at least the second emitter zone is doped with additional substances that act as dopants of the first conductivity type above the operating temperature of the semiconductor component. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing FIGURE represents a section through a semiconductor body of a GTO thyristor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The semiconductor body of the GTO thyristor of the drawing FIGURE has an inner zone 1 of the first conductivity type. A base zone 2 of the second conductivity type adjoins the inner zone 1. First emitter zones 3 that are of the same conductivity type as the inner zone, but which are significantly more highly doped than it adjoin the base zone 2. A second emitter zone 4, which is again of the second conductivity type, lies at the side opposite the base zone 2. The second emitter zone 4 is punctured by short-circuit zones 5 that have the same conductivity type as the inner zone 1, but have a higher doping than it. The short-circuit zones 5 usually have a greater depth than the second emitter zone 4. 
     The first emitter zones 3 are connected to emitter electrodes 6 that are connected parallel to one another. The second emitter zones and the short-circuit zones 5 are connected to an electrode 8. The base zone 2 is contacted to a control electrode 7. It is connected to a control terminal G. In a GTO thyristor, the zone sequence from the first emitter zones 3 up to the second emitter zone 4 is usually npnp. The electrodes 6 thus form the cathode terminal K and the electrode 8 forms the anode terminal A. 
     When such a GTO thyristor is turned off proceeding from the conductive condition, current lines or filaments where the current density is locally substantially higher than in the rest of the semiconductor body can form due to the initially cited, unavoidable inhomogeneities in the semiconductor body. The current density can become so high therein that the semiconductor body melts. In order to avoid these current lines or filaments, at least the second emitter 4 is then doped with additional substances in addition to the standard dopants of the second conductivity type such as, for example, boron. These dopants are selected such that they act as dopants of the first conductivity type above the operating temperature, i.e. at 300° C. and above, whereas they are electrically active to only a relatively slight extent at the normal operating temperature. For the standard case where the second emitter zone is p-doped, these additional substances must thus have donor properties at 300° C. Molybdenum, niobium, cesium or barium, for example, come into consideration as additional substances having such donor properties. In that case wherein the opposite zone sequence is present and the second emitter 4 is n-doped, the additional substances must have acceptor properties above the operating temperature. Cadmium, zinc, gold, or nickel, fix example, are substances suitable therefor. 
     What these substances have in common is that, dependent on the doping concentration of the first substances, they partially or entirely compensate the doping of the emitter zone 4 above the operating temperature, i.e. at about 300° C. and above. For a complete compensation of the first dopants present in the second emitter zone 4, the doping concentration of the additional substances should be as high as that of the first substances. 
     The additional substances thus have a compensating effect when the current lines or filaments form and the temperature therein rises. The emitter efficiency of the sub-transistor of the anode side composed of the zones 2, 1 and 4 is therefore locally reduced in the current lines. The reduction of the current amplification factor corresponds to a reduction of the current flowing in these lines or filaments upon turn-off, so that the turn-off current becomes more uniform overall. 
     The additional substances, however, can also be introduced beyond the second emitter into the adjoining region of the inner zone 1. However, they should not be introduced more deeply than the depth of the short-circuits 5, i.e., for example, down to a depth that is illustrated by the broken line 9. Given a temperature elevation in the lines or filaments, the additional substances act like an increase in the doping in the region of the inner zone 1 adjoining the second emitter zone 4. Since the current amplification is dependent on the ratio of the dopant concentration at both sides of the pn-junction, boosting the dopant concentration in the region of the inner zone 1 and lowering the effective dopant concentration in the zone 4 effects an overall reduction of the current amplification factor within the current lines or filaments. As a result thereof, the current amplification factor of the anode side in the current lines or filaments can be reduced to zero. The lines or filaments thus disappear, the temperature drops, and the current amplification factor of the anode side can rise again until an equilibrium is established. A significantly more uniform turn-off current then flows to the control electrode 7 in this condition. 
     The remaining region of the inner zone 1, the base zone 2 and the first emitter zone 3 remain free of additional substances. A doping of the short-circuit zones 5 with the additional substances does not deteriorate their effect. 
     Although various minor changes and modifications might be proposed by those skilled in the art, it will be understood that I wish to include within the claims of the patent warranted hereon all such changes and modifications as reasonably come within my contribution to the art.