Santa Barbara Research Center

Raytheon Company

Kenneth Kosai

George R Chapman

James A Finch

Scott M Taylor

Michael D Jack

David R Rhiger

Jerry A Wilson

Bonnie A Baumgratz

Joan K Chia

Chao Huang

Ken J Ando

A photodetector () includes a substrate () having a surface; a first layer () of semiconductor material that is disposed above the surface, the first layer containing a first dopant at a first concentration for having a first type of electrical conductivity; and a second layer () of semiconductor material overlying the first layer. The second layer contains a second dopant at a second concentration for having a second type of electrical conductivity and forms a first p-n junction () with the first layer. The second layer is compositionally graded through at least a portion of a thickness thereof from wider bandgap semiconductor material to narrower bandgap in a direction away from the p-n junction. The compositional grading can be done in a substantially linear fashion, or in a substantially non-linear fashion, e.g., in a stepped manner. Preferably the first dopant concentration is at least an order of magnitude greater than the second concentration, and more preferably is at least two orders of magnitude greater. When the first p-n junction is reverse biased, a depletion region () exists substantially only within the second layer, and varying the magnitude of the reverse bias shifts the wavelength at which a maximum spectral sensitivity or responsiveness is obtained. At least one electrical contact is provided for coupling the second layer to a source () of variable bias voltage for reverse biasing the p-n junction. As the magnitude of the bias voltage is changed a wavelength of electromagnetic radiation to which the photodetector is responsive is thus changed. An alternating current signal can be superimposed on the reverse DC bias voltage and a synchronous detection technique used to detect photons corresponding to a certain bandgap energy.

Photodiode having voltage tunable spectral response

A photodetector ( ) includes a substrate ( ) having a surface; a first layer ( ) of semiconductor material that is disposed above the surface, the first layer containing a first dopant at a first concentration for having a first type of electrical conductivity; and a second layer ( ) of semiconductor material overlying the first layer. The second layer contains a second dopant at a second concentration for having a second type of electrical conductivity and forms a first p-n junction ( ) with the first layer. The second layer is compositionally graded through at least a portion of a thickness thereof from wider bandgap semiconductor material to narrower bandgap in a direction away from the p-n junction. The compositional grading can be done in a substantially linear fashion, or in a substantially non-linear fashion, e.g., in a stepped manner. Preferably the first dopant concentration is at least an order of magnitude greater than the second concentration, and more preferably is at least two orders of magnitude greater. When the first p-n junction is reverse biased, a depletion region ( ) exists substantially only within the second layer, and varying the magnitude of the reverse bias shifts the wavelength at which a maximum spectral sensitivity or responsiveness is obtained. At least one electrical contact is provided for coupling the second layer to a source ( ) of variable bias voltage for reverse biasing the p-n junction. As the magnitude of the bias voltage is changed a wavelength of electromagnetic radiation to which the photodetector is responsive is thus changed. An alternating current signal can be superimposed on the reverse DC bias voltage and a synchronous detection technique used to detect photons corresponding to a certain bandgap energy.

An array (41) is comprised of a plurality of radiation detectors (10, 10') each of which includes a first photoresponsive diode (D1) having an anode and a cathode that is coupled to an anode of a second photoresponsive diode (D2). The first photoresponsive diode responds to electromagnetic radiation within a first band of wavelengths and the second photoresponsive diode responds to electromagnetic radiation within a second band of wavelengths. Each radiation detector further includes a first electrical contact (26) that is conductively coupled to the anode of the first photoresponsive diode; a second electrical contact (28) that is conductively coupled to the cathode of the first photoresponsive diode and to the anode of the second photoresponsive diode; and a third electrical contact (30) that is conductively coupled to a cathode of each second photoresponsive diode of the array. The electrical contacts are coupled during operation to respective bias potentials. The first electrical contact conducts a first electrical current induced by electromagnetic radiation within the first predetermined band of wavelengths, and the second electrical contact conducts a second electrical current induced by electromagnetic radiation within the second predetermined band of wavelengths less an electrical current induced by electromagnetic radiation within the first predetermined band of wavelengths.

Simultaneous two-wavelength p-n-p-n Infrared detector

An imaging device (10, 10') has a plurality of unit cells (11) that contribute to forming an image of a scene. The imaging device includes a layer of wide bandgap semiconductor (18) material (e.g., silicon) having photogate charge-mode readout circuitry (20, 22, 24), such as CCD or CMOS circuitry, disposed upon a first surface of the layer. In one embodiment a second, opposing surface of the layer is bonded at a heterojunction interface or atomic bonding layer (16) to a surface of a layer of narrower bandgap semiconductor material (e.g., InGaAs or HgCdTe), that is selected for absorbing electromagnetic radiation having wavelengths longer than about one micrometer (i.e., the NIR or longer) and for generating charge carriers. The generated charge carriers are transported across the heterojunction interface for collection by the photogate charge-mode readout circuitry. The layer of narrower bandgap material may be disposed upon a surface of a transparent substrate, and also may be differentiated into a plurality of mesa structures (14a). In further embodiments the absorbing layer may have an equivalent or a wider bandgap than the layer having the readout circuitry.

Low light level imager with extended wavelength response employing

A solid state array has a plurality of radiation detector unit cells, wherein each unit cell includes a bias-selectable two color photodetector in combination with either a second bias-selectable two color detector (10, 11) or a single photodetector (10', 11'). Each unit cell is thus capable of simultaneously outputting charge carriers resulting from the absorption of electromagnetic radiation within two spectral bands that are selected from one of four spectral bands and three spectral bands.

Three band and four band multispectral structures having two

A radiation detector (1) unit cell (10) includes an n-p+ LWIR photodiode that is vertically integrated with a p+-n MWIR photodiode in a n-p+-n structure. Electrical contact is made separately to each of these layers in order to simultaneously detect both the LWIR and MWIR bands. The electrical contact is made via indium bump interconnections (23, 25, 27) enabling the unit cell to be subsequently hybridized with a topside mounted electronic readout integrated circuit (30). The n-p+-n structure in a given pixel of an array of radiation detector pixels is electrically isolated from all neighboring pixels by a trench (28) that is etched into an underlying substrate (12). To compensate for a reduction in the optically sensitive area due to the placement of the electrical contacts and the presence of the pixel isolation trench, a microlens (34) may be provided within, upon, or adjacent to the backside, radiation receiving surface of the substrate in registration with the unit cell.

Integrated LPE-grown structure for simultaneous detection of infrared

A dual-band HgCdTe radiation detector (10) includes a four layer n-p.sup.+ -p-n.sup.+ structure, grown by LPE, upon a substrate (12). The four layers are, from a bottom layer next to the substrate to the surface: (a) a MWIR radiation responsive n-type absorbing layer (14); (b) a p.sup.+ cap layer (16); (c) a LWIR radiation responsive p-type layer (18); and (d) an n+ top layer (20). The n.sup.+ top layer has a compositional profile that is similar to the p-type cap layer. Operation of this structure involves biasing the top layer positive with respect to the bottom layer, which results in the collection of LWIR-generated electrons in the p-type layer. Biasing the top layer negative with respect to the bottom layer results in MWIR-generated holes being collected by the bottom n-p+ junction. In this mode, however, the detector structure rejects collection of LWIR-generated electrons because a compositional profile of the two p-type layers prevents the electrons from drifting to the bottom n-p+ junction and being collected.

Dual-band infrared radiation detector optimized for fabrication in

An uncooled thermal detector (10) includes a MIS capacitor (12) that is suspended from a material (26, 26a) having a low thermal conductivity. The MIS capacitor includes a doped semiconductor body portion (14) having a gate dielectric (20), a gate electrode (22), and a second electrode (24) disposed over a surface thereof. In operation, the capacitance of the MIS capacitor at a frequency near a high-frequency/low-frequency transition is measured or sensed. As the temperature of the MIS capacitor increases, the sensed capacitance increases because minority carriers are able to respond faster to a modulating gate voltage. Similarly, if the temperature decreases, the sensed capacitance decreases, because the minority carriers respond more slowly. A high thermal coefficient of capacitance (&gt; 20%/K) is achieved at all gate bias values for which the MIS capacitor is in inversion. By a suitable choice of doping level and the introduction of a deep level (24) to control the minority-carrier lifetime, the transition frequency may be tailored to a desired operating frequency at a given temperature. A method for fabricating the uncooled detector, and an array of same, within a Si film (2) of an SOI wafer (1) is also disclosed.

Uncooled mis capacitor for infrared detection

A mercury-cadmium-telluride (HgCdTe) photoresponsive layer (14) having the composition Hg.sub.1-x Cd.sub.x Te is formed on a substrate (12) such that x increases from the surface (14a) of the photoresponsive layer (14) toward the substrate (12). This causes the bandgap in the photoresponsive layer (14) to increase from the surface (14a) toward the substrate (12), thereby urging minority carriers which are photogenerated in the photoresponsive layer (14) to move toward and be trapped at the surface (14a). Laterally spaced first and second ohmic contacts (16,18) are electrically connected to the photoresponsive layer (14) at a predetermined distance (z.sub.c) below the surface (14a) such that the photogenerated minority carriers trapped at the surface (14a) are urged away from the contacts (16,18) by the increasing bandgap. An electrically floating photoresponsive layer (24) of opposite conductivity type may be formed between the substrate (12) and the photoresponsive layer (14) to form a Heterojunction Interface Trap.

Photoresponsive device including composition grading and recessed

A MIS semiconductor device comprises a crystalline substrate having a first energy band gap and a crystalline passivation layer overlying a surface of the substrate. The passivation layer is comprised of a semiconductor material having a wider band gap than the semiconductor material of the substrate. In an illustrative embodiment of the invention a MIS semiconductor device comprises a mercury-cadmium-telluride (HgCdTe) substrate having a cadmium-telluride (CdTe) heterojunction formed thereon, the CdTe functioning as a layer of high-quality passivation. A metal gate insulator may be SiO.sub.2, low temperature CVD Si.sub.3 N.sub.4, or any other suitable insulator deposited at a relatively low temperature.

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Goleta, CA, United States of America

Kenneth Kosai