Semiconductor device for generating an electron beam and method of manufacturing same

A semiconductor device for generating an electron beam by avalanche multiplication across a reverse biased P-N junction, comprising:

• a semiconductor body having a surface, said body comprising:
• a surface-adjoining N-type conductivity region;
• and
• a P-type conductivity region adjoining the N-type region, said P-type and
• N-type regions forming a P-N junction therebetween, said P-N junction having at least a portion which (a) is substantially parallel to the surface of the semiconductor body and (b) has a lower breakdown voltage than at other portions of the junction;
• an electrically insulating layer on the surface of the semiconductor body, said layer having an aperture therethrough over at least the portion of the P-N junction which is parallel to the surface and which has a lower breakdown voltage;
• and
• an accelerating electrode provided on the insulating layer at the edge of the aperture;
• wherein the portion of the P-N junction having a lower breakdown voltage is separated from the surface of the semiconductor body by the N-type region, said N-type region having a thickness and dopant concentration such that at the breakdown voltage a depletion region around the reduced breakdown voltage portion of the P-N junction is separated from the surface by a nondepleted surface layer which is sufficiently thin to pass the generated electrons.