Texas Instruments Corporation

Drs Sensors & Targeting Systems, Inc.

Drs Network & Imaging Systems, LLC

Drs Rsta, Inc.

Michael A Kinch

Richard A Chapman

Jeffrey Don Beck

Christopher A Schaake

Jaroslav Hynecek

John H Tregilgas

Dennis D Buss

Arturo Simmons

Herbert F Schaake

Roland J Koestner

Richard A Schiebel

Pradip Mitra

Chang-Feng Wan

Adam J Lewis, Jr

C Grady Roberts

Disclosed are minority carrier based mercury-cadmium telluride (HgCdTe) infrared detectors and arrays, and methods of making, are disclosed. The constructions provided by the invention enable the detectors to be used at higher temperatures, and/or be implemented on less expensive semiconductor substrates to lower manufacturing costs. An exemplary embodiment a substrate, a bottom contact layer disposed on the substrate, a first mercury-cadmium telluride layer having a first bandgap energy value disposed on the bottom contact layer, a second mercury-cadmium telluride layer having a second bandgap energy value that is greater than the first bandgap energy value disposed on the first mercury-cadmium telluride layer, and a collector layer disposed on the second mercury-cadmium telluride layer, wherein the first and second mercury-cadmium telluride layers are each doped with an n-type dopant.

Minority carrier based HgCdTe infrared detectors and arrays

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

A photodiode for detection of preferably infrared radiation capable of detecting two different wavelengths wherein photons are absorbed in one region and detected in another. In one example embodiment, an absorbing P region is abutted with an N region of lower doping such that the depletion region is substantially (preferably completely) confined to the N region. The N region is also chosen with a larger bandgap than the P region, with compositional grading of a region of the N region near the P region. This compositional grading mitigates the potential barrier between the respective bandgaps. Under first voltage conditions a potential barrier prevents minority carriers from moving from the P region to the N region, but photons of energy large enough to generate minority carriers within the N region are detected. Under reverse bias, the barrier is substantially reduced or disappears, allowing charge carriers to move from the absorbing P region into the N region (and beyond) where they are detected. Thus, under reverse bias, both wavelengths of energy can be detected, and separated by differencing the output.

Separate absorption and detection diode for two-color operation

A photodiode for detection of preferably infrared radiation wherein photons are absorbed in one region and detected in another. In one example embodiment, an absorbing P region is abutted with an N region of lower doping such that the depletion region is substantially (preferably completely) confined to the N region. The N region is also chosen with a larger bandgap than the P region, with compositional grading of a region of the N region near the P region. This compositional grading mitigates the barrier between the respective bandgaps. Under reverse bias, the barrier is substantially reduced or disappears, allowing charge carriers to move from the absorbing P region into the N region (and beyond) where they are detected. The N region bandgap is chosen to be large enough that the dark current is limited by thermal generation from the field-free p-type absorbing volume, and also large enough to eliminate tunnel currents in the wide gap region of the diode.

Separate absorption and detection diode

A photodiode for detection of preferably very long wavelength infrared radiation wherein low energy photons are absorbed in one region and detected in another. In one example embodiment, an absorbing P region is abutted with an N region of lower doping such that the depletion region is substantially (preferably completely) confined to the N region. The N region is also chosen with a larger bandgap than the P region, with compositional grading of a region of the N region near the P region. This compositional grading mitigates the barrier between the respective bandgaps. Under reverse bias, the barrier is substantially reduced or disappears, allowing charge carriers to move from the absorbing P region into the N region (and beyond) where they are detected. The N region bandgap is chosen to be large enough that the dark current is limited by thermal generation from the field-free p-type absorbing volume, and also large enough to eliminate tunnel currents in the wide bandgap region of the diode.

Separate absorption and detection diode for VLWIR

Group II-VI thin film transistors, a method of making same and a monolithic device containing a detector array as well as transistors coupled thereto wherein, according to a first embodiment, there is provided a group II-VI insulating substrate, a doped layer of a group II-VI semiconductor material disposed over the substrate, an insulating gate region disposed over the doped layer, a pair of spaced contacts on the doped layer providing source and drain contacts, a gate contact disposed over the insulating gate region, an insulating layer disposed over exposed regions of the substrate, doped layer, insulating gate region and contacts and metallization disposed on the insulating layer and extending through the insulating layer to the contacts. The thickness of the doped layer is less than the maximum depletion region thickness thereof. In accordance with a second embodiment, there is provided a group II-VI insulating substrate, a first conductive doped group II-VI semiconductor layer disposed over the substrate, a second doped group II-VI layer disposed over the first layer and forming a Schottky barrier therewith, an insulating layer disposed over exposed regions of the substrate, first doped layer and second doped layer and metallization disposed on the insulating layer and extending through the insulating layer to spaced regions on the first layer to form source and drain contacts thereto and to the second layer to form a gate contact thereto. The thickness of said first layer is less than the maximum depth of the depletion region formed by the junction of the first and second layers.

HGCDTE thin film transistor

Method of making a HgCdTe thin film transistor

Photocapacitive detectors with varying bandgap Hg.sub.1-x Cd.sub.x Te (604) for two color detection and one color detection with increased potential well capacity. Preferred embodiments include a transparent insulated gate (608) on a top layer (632) of Hg.sub.0.8 Cd.sub.0.2 Te over a lower layer (634) of Hg.sub.0.83 Cd.sub.0.27 Te for detection of two infrared colors by varying gate potential to either confine the potential well to the top layer or to extend the potential well to both layers. Also, methods of compositionally grading the Hg.sub.1-x Cd.sub.x Te by fluid transport plus diffusion.

Infrared detector and method

The disclosure relates to oxide-semiconductor interfaces which are grown with varying amounts of fixed positive (or negative) charge. The invention utilizes these different values to form a channel stop for a charge transfer device. For HgCdTe two different oxides are used, namely, those produced by wet anodization (having large values of fixed positive charge) and plasma oxidation (having low values of fixed charge). The voltage range of operation of the active gate is determined by the difference in fixed positive charge for these regions and the insulator thicknesses.

Dual oxide channel stop for semiconductor devices

The disclosure relates to a stepped insulator process for HgCdTe infared focal plane devices, the insulator being a combination of two insulator materials, ZnS and SiO, which differ in dielectric constant and chemical reactivity. The structure is patterned on HgCdTe which has an accumulated surface region. The resulting configuration significantly reduces pin hole short circuits introduced during via etching and improves the operating range (channel stopping action) for a given step height over that of ZnS alone.

Mercury cadmium telluride infrared focal plane devices having step

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 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.

Method of producing homogeneously doped HgCdTe which contains a fast

A monolithic charge-coupled infrared imaging device (CCIRID) is fabricated on N-type HgCdTe. A native oxide layer on the semiconductor is used, in combination with ZnS to provide first level insulation. An opaque field plate over first level insulation is provided for signal channel definition. Second level insulation (ZnS) is substantially thicker than the first level, and is provided with a stepped or sloped geometry under the first level gates. Input and output diodes are provided with MIS guard rings to increase breakdown voltages.

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Dallas, TX, United States of America

Michael A Kinch