Santa Barbara Research Center

Lockheed Martin Corporation

Raytheon Company

Hughes Aircraft Company

Charles A Cockrum

Eric Frank Schulte

Jeffrey Winfield Scott

Ernie J Caine

Colin E Jones

David R Rhiger

Joseph P Rosbeck

Francis I Gesswein

Wallace Y Kunimoto

Jeffrey Brian Barton

Joan K Chia

Peter R Bratt

Owen K Wu

James F Kreider

A method of making a two-dimensional detector array (and of such an array) comprising, for each of a plurality of rows and a plurality of columns of individual detectors, forming an n-doped semiconductor photo absorbing layer, forming a bather layer comprising one or more of AlSb, AlAsSb, AlGaAsSb, AlPSb, AlGaPSb, and HgZnTe, and forming an n-doped semiconductor contact area.

Sub-pixel nBn detector

A method of making a two-dimensional detector array (and of such an array) comprising, for each of a plurality of rows and a plurality of columns of individual detectors, forming an n-doped semiconductor photo absorbing layer, forming a barrier layer comprising one or more of AlSb, AlAsSb, AlGaAsSb, AlSb, AlGaPSb, and HgZnTe, and forming an n-doped semiconductor contact area.

Sub-pixel NBN detector

A method of making a two-dimensional detector array (and of such an array) comprising, for each of a plurality of rows and a plurality of columns of individual detectors, forming an n-doped semiconductor photo absorbing layer, forming a barrier layer comprising one or more of AlSb, AlAsSb, AlGaAsSb, AlPSb, AlGaPSb, and HgZnTe, and forming an n-doped semiconductor contact area.

An array 1 of photodiodes 2 is comprised of a Group II-VI material, such as HgCdTe, which may be selectively doped to form a plurality of diode junctions. Array 1 is comprised of a plurality of photodiodes 2 which are disposed in a regular, two dimensional array. Incident IR radiation, which may be long wavelength, medium wavelength or short wavelength (LWIR, MWIR or SWIR) radiation, is incident upon a surface of the array 1. The array 1 comprises a radiation absorbing base layer 3 of Hg.sub.1-x Cd.sub.x Te semiconducting material, the value of x determining the responsivity of the array to either LWIR, MWIR or SWIR. Each of the photodiodes 2 is defined by a mesa structure, or cap layer 3; or the array 1 of photodiodes 2 may be a planar structure. Each of the photodiodes 2 is provided with an area of contact metallization 4 upon a top surface thereof, the metallization serving to electrically couple an underlying photodiode to a readout device. The upper surface of the array 1 is provided with, in accordance with the invention, a passivation layer 5 comprised of an epitaxial layer of Group II-VI material which forms a heterostructure with the underlying Group II-VI material and which has a wider bandgap than the underlying Hg(.sub.1-x)Cd.sub.x Te, thereby beneficially repelling both holes and electrons from the diode junctions.

Epitaxial passivation of group II-VI infrared photodetectors

A Group II-VI IR photodiode 10 has a passivation layer 16 overlying at least exposed surfaces of the p-n diode junction 15, the passivation layer being a compositionally graded layer comprised of Group II atoms diffused into a surface of the p-n diode junction. The passivation layer has a wider energy bandgap than the underlying diode material thereby repelling both holes and electrons away from the surface of the diode and resulting in improved diode operating characteristics. A cation substitution method of the invention includes the steps of preparing a surface to be passivated, such as by depleting an upper surface region of Group II atoms; depositing a layer comprised of a Group II material over the depleted surface region; and annealing the deposited layer and underlying Group II-VI material such that atoms of the deposited Group II layer diffuse into the underlying depleted surface region and fill cation vacancy sites within the depleted surface region. The resulting passivation layer is a compositionally graded layer having an energy bandgap which gradually decreases in value as a function of depth from the surface until the bandgap energy equals that of the underlying bulk material. The preparation of the surface may also be accomplished by providing a body of Group II-VI material which has a substantially stoichiometric composition.

Graded layer passivation of group II-VI infrared photodetectors

A photoresponsive device (10) includes a body comprised of semiconductor material comprised of elements selected from Group IIB-VIA; and at least one electrically conductive contact pad (20) formed over a surface of the semiconductor material. The at least one electrically conductive contact pad is comprised of metal nitride, such as MoN, and serves as a diffusion barrier between an Indium bump (22a, 22b) and the underlying semiconductor material. A passivation layer (18), such as a layer of wider bandgap CdTe, can be formed to overlie the surface of said semiconductor material. A p-n junction is contained within a mesa structure (10a) that comprises a portion of an n-type base layer (14) and a p-type cap layer (16). A first contact pad is disposed over the cap layer and a second contact pad is disposed over the base layer. The device further includes a first layer (24a) comprised of Au that is disposed between a bottom surface of the first contact pad and the cap layer; a second layer (24b) comprised of Cr that is disposed between a bottom surface of the second contact pad and the base layer; and a third layer (26) comprised of nickel that is disposed upon a top surface of the first and second contact pads. A first In bump (22a) is disposed upon the third layer over the first contact pad and a second indium bump (22b) disposed upon the third layer over the second contact pad. The metal nitride is applied, preferably, by a reactive sputtering technique.

Contact metal diffusion barrier for semiconductor devices

A compositionally graded HgCdTe radiation detector (10) is constructed to have a high purity 'denuded zone' (Region 2) that is formed adjacent to a radiation absorbing region (Region 1). The compositional grading results in an internally generated electric field that is orthogonally disposed with respect to an externally generated electric field applied between contacts (16, 18). The internally generated electric field has the effect of injecting photogenerated minority charge carriers into the denuded zone, thereby reducing recombination with photogenerated majority charge carriers and increasing carrier lifetime. The detector further includes a wider bandgap surface passivation region (Region 3) that functions to trap, or 'getter', impurities from the denuded zone and also to reduce surface recombination effects.

Denuded zone field effect photoconductive detector

A photoresponsive device wherein the device includes semiconductor material, such as a cap region (14a), comprised of elements selected from Group IIB-VIA. A molybdenum contact pad (16) is formed upon a surface of the cap region, and a molybdenum ground contact pad is formed on a surface of a base region (12). A wide bandgap semiconductor passivation layer (20) overlies the surface of the cap region and also partially overlies the molybdenum contact pad. A dielectric layer (22) overlies the passivation layer, and an indium bump (24) is formed upon the molybdenum contact pad. The dielectric layer is in intimate contact with side surfaces of the indium bump such that no portion of the molybdenum contact pad can be physically contacted from a top surface of the dielectric layer. This method eliminates the possibility of unwanted chemical reactions occurring between the In and the underlying contact pad metal. The method also deposits the contact metal before the deposition of the passivation and before a high temperature anneal, with windows to the contact being opened after the anneal so as to reduce localized stresses at the edges of the windows.

Bake-stable HgCdTe photodetector with II-VI passivation layer

A photoresponsive device and a method of fabricating same, wherein the device includes semiconductor material, such as a cap region (14a), comprised of elements selected from Group IIB-VIA. A molybdenum contact pad (16) is formed upon a surface of the cap region, and a molybdenum ground contact pad is formed on a surface of a base region (12). A wide bandgap semiconductor passivation layer (20) overlies the surface of cap region and also partially overlies the molybdenum contact pad. A dielectric layer (22) overlies the passivation layer, and an indium bump (24) is formed upon the molybdenum contact pad. The indium bump extends upwardly from the molybdenum contact pad and through the dielectric layer. The dielectric layer is in intimate contact with side surfaces of the indium bump such that no portion of the molybdenum contact pad can be physically contacted from a top surface of the dielectric layer. The method eliminates the possibility of unwanted chemical reactions occurring between the In and the underlying contact pad metal. The method also deposits the contact metal before the deposition of the passivation and before a high temperature anneal, with windows to the contact being opened after the anneal so as to reduce localized stresses at the edges of the windows.

Bake-stable HgCdTe photodetector and method for fabricating same

An infrared detector assembly (12) of the type used in munitions and night vision systems having an improved focal plane platform (10) construction. In accordance with this invention, the thermally conductive focal plane platform (10) supports a detector array (26) and integrated readout chips (28). The focal plane platform (10) includes relatively thermally non-conductive inserts (38) disposed in cavities (36) positioned generally below each integrated read out chip (28). The inserts insulate the chips (28) during cryogenic cooling of detector array (26). Freeze-out of the chips (28) is thereby inhibited.

Infrared detector focal plane

An array of photovoltaic radiation detectors and a method of fabricating same. The array 10 includes a substrate 12 substantially transparent to radiation having wavelengths of interest and a radiation absorbing base layer 14 having a first surface 14a overlying a surface of the substrate for admitting incident radiation into the base layer. The base layer is comprised of a compositionally graded p-type Hg.sub.1-x Cd.sub.x Te material wherein x equals approximately 0.6 to approximately 0.8 at the first surface and equals less than approximately 0.4 at a second surface 14b. A cap layer 16 overlies the second surface of the radiation absorbing base layer, the cap layer also being compositionally graded. The cap layer has a bandgap that increases in width as a function of distance from the second surface of the base layer. The array further includes a plurality of regions 18 formed through the top surface of and substantially wholly within the wide bandgap cap layer, each of the regions forming a p-n junction 18a with the underlying material of the cap layer for collecting charge carriers. A plurality of channels 22 prevent lateral diffusion of charge carriers through the base layer.

Heterojunction photodiode array

An array of photodiodes is comprised of a Group II-VI material, such as HgCdTe, which is processed to form a plurality of diode junctions. The array is fabricated by a method which comprises a first step of providing a radiation absorbing base 12 of p-type Hg.sub.(1-x) Cd.sub.x Te material. Each of the photodiodes is fabricated by depositing a layer 18 of wider bandgap passivation material over the substrate, depositing a photomask layer 26 over the passivation layer and selectively removing the passivation layer through openings within the photomask layer. One method of removing the passivation layer 18 is by ion milling which also converts the underlying p-type substrate material to n-type material. The lattice damage caused by the ion milling extends laterally outward such that the n-type region 14, and associated p-n diode junction 16, is disposed beneath the passivation layer 18. Alternatively, the substrate material is converted to an opposite type of conductivity by depositing a layer of source material followed by a diffusion process.

Buried junction infrared photodetector process

Metallic contacts to compound semiconductor devices which employ a native oxide for passivation are provided. The metallic contacts of the invention comprise at least two metal layers: a first layer making non-rectifying contact with the semiconductor surface and providing a diffusion barrier and a second layer thereon comprising an easily oxidizable metal. A low resistivity metal layer may optionally be interposed between the two metal layers for improved conductivity. The metallic contact is formed prior to passivation. The diffusion barrier layer prevents diffusion of potentially deleterious materials into the semiconductor, while exposed portions of the oxidizable metal form an insulating oxide during anodic passivation in an electrolyte. The insulating oxide prevents disruption of the electric field distribution in the electrolyte, thereby eliminating passivating oxide and device non-uniformities commonly encountered in the formation of prior art metallic contacts and providing more uniform semiconductor oxide thickness.

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Goleta, CA, United States of America

Charles A Cockrum