Westinghouse Electric Corporation

Krishan S Tarneja

John Bartko

Joseph E Johnson

Chang K Chu

Earl S Schlegel

Patrick E Felice

A method of reducing the reverse recovery charge of thyristors without substantially increasing forward voltage drop by first determining the depth of the anode PN junction from a major surface adjoining a cathode emitter region. The depth of maximum defect generation in thyristor on irradiation through the major surface with a given radiation source radiating particles with molecular weight greater than one, preferably proton or alpha particles, and adjusting the energy level at the major surface of the thyristor from the radiation source to provide the depth of maximum defect generation adjacent the anode PN junction and preferably in the anode base region within 20 micrometers of the anode PN junction or in the anode emitter region within 15 micrometers of the anode PN junction. Thereafter the thyristor is irradiated through said major surface with the adjusted energy level from the radiation source to a given dosage to reduce the reverse recovery stored charge of the thyristor without substantially increasing the forward voltage drop.

Reducing the reverse recovery charge of thyristors by nuclear irradiation

The switching time of certain semiconductor devices is decreased while maintaining other electrical characteristics of the devices by irradiating them with a neutron radiation source of greater than 1.0 Mev. to a dosage between 1.times.10.sup.11 and 1.times.10.sup.15 neutrons per square centimeter. The irradiation is preferably to a dosage between 1.times.10.sup.1 and 1.times.10.sup.14 neutrons per square centimeter and preferably has substantial energy greater than 14 Mev. The devices are also annealed during and/or subsequent to the irradiation at a temperature higher than the highest specified temperature and preferably at least 50.degree. C. higher than the highest specified temperature.

Reducing the switching time of semiconductor devices by neutron

The recovery charge of power diodes and thyristors is tailored and matched by irradiation through a major surface of the semiconductor body with a given radiation source, preferably of electron radiation, to a dosage corresponding to between about 1 .times. 10.sup.12 and 8 .times. 10.sup.12 electrons per centimeter square with 2 MeV electron radiation. Preferably, the recovery charge of each device of a group of a type of diode or thyristor is first measured, and the group divided into subgroups according to the measured recovery charge of each device. The devices of at least one subgroup is then irradiated with said given radiation source to dosages corresponding to between about 1 .times. 10.sup.12 and 8 .times. 10.sup.12 electrons per centimeter square with 2 MeV electron radiation, and the recovery charge of each irradiated device is again measured to determine the incremental change of recovery charge as a function of irradiation dosage. A recovery charge of another device of said type of diode or thyristor is then measured, and the device irradiated with said radiation source to a determined dosage corresponding to a desired incremental change in recovery charge to tailor the recovery charge of said device to a desired value.

Tailoring of recovery charge in power diodes and thyristors by

Diodes of a particular type are fine tuned with irradiation to optimize the reverse recovery time while minimizing forward voltage drop and providing more uniform electrical characteristics. The initial and desired minority carrier lifetimes in the anode region of the type are determined as a function of forward voltage drop and reverse recovery time, and the minority carrier radiation damage factor is determined for a desired type of diode and radiation source. The radiation dosage to achieve the desired carrier lifetime with the radiation source is thereafter determined from the function 1/.tau. = 1/.tau..sub.o + K.phi., where .tau. is the desired minority carrier lifetime, .tau..sub.o is the initial minority carrier lifetime, K is the determined minority carrier radiation damage factor and .phi. is the radiation dosage. A major surface and preferably the major surface adjoining the anode region of the diodes is then irradiated with the radiation source to the determined radiation dosage. Preferably, the radiation dosage is between about 1 .times. 10.sup.12 and 5 .times. 10.sup.13 e/cm.sup.2, with electron radiation of intensity between 1 and 3 Mev.

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Pittsburgh, PA, United States of America

Krishan S Tarneja