Coaxial gamma ray detector and method therefor

A gamma-ray radiation detector comprising:

• a. a cylindrical body of high purity intrinsic germanium,
• b. a diffused region of electrical impurity material covering at least the cylindrical surface of said body and extending within said body,
• c. first means for making electrical contact with said diffused region,
• d. second means for making electrical contact with said body,
• e. first and second means adapted for connection to a voltage source for reverse biasing said detector thereby forming a depletion zone within a major portion of said body, and
• f. means for isolating said depletion zone from said second means thereby preventing runaway leaking currents during full depletion, high reverse bias operations.

A method for fabricating a solid state radiation detector from a semiconductor body having a lateral surface and first and second opposing planar surfaces, said detector possessing high sensitivity and being capable of withstanding high reverse bias voltage without exhibiting catastrophic, steady-state leakage current, comprising the steps of:

• a. forming a recess along the longitudinal axis of said semiconductor
• b. depositing an electrical impurity materialf selectively upon said lateral surface and said planar surfaces in a pattern defining an impurity-free region on said first planar surface exteriorally concentric and adjacent to said recess;
• c. diffusing said electrical impurity material into said semiconductor body to yield an outer impurity region corresponding in extent to the area of said depositing and in penetration to a thickness substantially less than the overall thickness of said body;
• d. forming an annular groove in said first planar surface exteriorly concentric of said recess in the space between said recess and said impurity region, the depth of said groove being at least equal to the thickness of said outer impurity region, said groove defining a shoulder of intrinsic semiconductor material intermediately concentric said recess and said groove;
• e. depositing a layer of electrically-conductive material at least upon the internal surface of said recess;
• and
• f. providing a first electrical contact to said outer impurity region and a second electrical contact adjacent said shoulder.

A method for detecting electromagnetic radiation emanating from a radiative source comprising the steps of:

• a. applying a reverse bias voltage across a solid state radiation detector formed from a semiconductor material having:
• i. a substantially thin impurity region selectively diffused within the surface of said semiconductor material in a pattern defining an impurity-free region;
• ii. a recess along the longitudinal axis of said detector;
• iii. an annular groove exteriorly concentric of said recess, said groove having an outer diameter coincident with the diameter of said impurity-free region, said groove further defining a shoulder of intrinsic semiconductor material intermediately concentric said recess and said groove;
• and,
• iv. a substantially thin layer of electrically-conductive material coated upon the internal surface of said recess;
• said reverse bias applied to electrical contact points, one of said contact points located on said electrical impurity region and another of said contact points located on said electrically-conductive material adjacent said shoulder;
• b. forming a depletion zone devoid of free electrical carriers within a region intermediate said electrical impurity region and said electrically-conductive material;
• c. allowing radiation from said source to impinge upon said detector whereby charge carriers are generated within said depletion zone thereby giving rise to an electrical signal;
• and,
• d. applying said electrical signal to analytical equipment to determine the characteristics of said radiative source.

A method of increasing the sensitivity of the active depletion zone during operation of a coaxial gamma ray detector without producing large runaway leakage currents comprising the steps of:

• forming a first electrical contact with an inner metallic layer at a region removed from the detector active depletion zone,
• forming a second electrical contact with an outer impurity zone;
• and
• applying a reverse bias voltage between said first and second contacts.