Texas Instruments Corporation

Drs Network & Imaging Systems, LLC

Drs Rsta, Inc.

Drs Sensors & Targeting Systems, Inc.

Jeffrey Don Beck

Pradip Mitra

John H Tregilgas

Michael A Kinch

Herbert F Schaake

Mark R Skokan

Chang-Feng Wan

A radiation detector is provided that includes a photodiode having a radiation absorber with a graded multilayer structure. Each layer of the absorber is formed from a semiconductor material, such as HgCdTe. A first of the layers is formed to have a first predetermined wavelength cutoff. A second of the layers is disposed over the first layer and beneath the first surface of the absorber through which radiation is received. The second layer has a graded composition structure of the semiconductor material such that the wavelength cutoff of the second layer varies from a second predetermined wavelength cutoff to the first predetermined wavelength cutoff such that the second layer has a progressively smaller bandgap than the first bandgap of the first layer. The graded multilayer radiation absorber structure enables carriers to flow toward a conductor that is used for measuring the radiation being sensed by the radiation absorber.

Radiation detector having a bandgap engineered absorber

An avalanche photodiode is operated in avalanche mode at a selected reverse bias that achieves high gain and a reduced gain normalized dark current.

Method of operating an avalanche photodiode for reducing gain normalized dark current

The disclosure relates to a method for reducing impurity concentration in mercury cadmium telluride alloys wherein impurities are attracted to a region saturated with second phase tellurium during annealing in a saturated mercury atmosphere where the second phase tellurium and the impurities attracted thereto can be removed by polishing, etching, grinding, or the like.

Impurity reduction technique for mercury cadmium telluride

The disclosure relates to a method for removing the unwanted impurities from an HgCdTe alloy which consists of the steps of depositing a thin film on the order of from about 1 to about 100 microns in thickness of tellurium onto the backside of a mercury cadmium telluride bar to insure the presence of a substantial amount of excess tellurium on the backside of the alloy bar and allow the gettering mechanism to work. A protective film to shield the tellurium film from mercury ambient atmosphere is then optionally placed over the tellurium film. The protective film can be formed of a silicon oxide such as SiO and is preferably in the range of about 1000 angstroms to 10 microns or more in thickness. The bar with the tellurium and protective film thereon is then annealed at a temperature of less than 450.degree. C., preferably about 280.degree. C., for a period of from about one day to about four weeks in a saturated mercury atmosphere to allow the impurities in the alloy to diffuse to the backside thereof and into the tellurium layer. The bulk of the impurities will travel into the tellurium layer within a matter of several days at the preferred temperature noted hereinabove. The tellurium layer and protective film are then removed such as by grinding, etching or other appropriate method to remove the impurities from the alloy bar.

Gettering method for mercury cadmium telluride

The disclosure relates to a method for making extrinsically doped HgCdTe alloys containing Cu, Ag, or Au or other dopant impurity whereby the excess tellurium in the core is annihilated (stoichiometrically compensated by excess in-diffusing Hg) and the dopant impurities are then permitted to randomly move through the slab to provide for homogeneity thereof. A post-annealing step of much greater than normal temperature-time length than was provided in the prior art is used. A standard post-annealing step in a saturated mercury vapor atomosphere leaves second phase tellurium (and gettered impurities) at the center of the slab, and longer term post-annealing negates this situation by annihilating the second phase tellurium in the slab and thus permitting the impurities to randomly travel by solid state diffusion throughout the slab to ultimately be distributed therein in a homogeneous manner. The additional time required for the post-annealing step following the normal prior art post-annealing step varies based upon slice or slab thickness, the metal-Te stoichiometry, and second post-annealing step temperature and, in general, will be longer but in the same range as that used in the prior post-annealing stage. Following annihilation of the second phase tellurium from the core, the impurity is homogenized in the slab by further annealing for from about one hour to about 20 weeks at a temperature under 300.degree. C., preferably 280.degree. C., by solid state diffusion.

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Plano, TX, United States of America

Jeffrey Don Beck