Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
1999-03-26
2001-01-30
Hardy, David (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S021000, C250S338400, C250S339030, C250S370140
Reexamination Certificate
active
06180990
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention pertains in general to radiation detectors, such as for infrared radiation, and in particular to such detectors, and systems which include such detectors, used for the simultaneous detection of multiple bands of radiation.
BACKGROUND OF THE INVENTION
The term “hyperspectral imaging” refers to the concurrent collection of radiation for multiple, adjacent spectral radiation bands to detect a target, which may be subpixel in size. The collection of radiation with different wavelengths at one time can provide greater information about whatever is present within the field of view, in particular it can make possible the detection of subpixel targets when the data is processed with appropriate algorithms. This is also referred to as the ability to image a scene in many spectral colors simultaneously. Hyperspectral detectors are frequently designed to operate in the infrared range of radiation. Such detectors have been designed to collect several hundred adjacent bands of radiation at one time.
The wide bandwidth radiation is collected by detectors which are sensitive to each of the bands of radiation. One method of separating the radiation by wavelength is by use of a prism. A further method of separation is accomplished by use of a diffraction grating.
Second generation photovoltaic mercury cadmium telluride (MCT) is difficult to manufacture in large two-dimensional arrays. In general it has poor uniformity, an excess of outages, and does not maintain the gain and offset calibration required for a hyperspectral detector system. As a result, it does not meet the requirements for a longwave infrared (LWIR) long range standoff targeting/surveillance system. Quantum Well Infrared Photodetectors (QWIPS) have an external Quantum Efficiency (QE) of approximately four percent (4%). This is a product of the internal quantum efficiency and the photoconductive gain. This value of QE is generally insufficient for a targeting/surveillance system which would operate at a range of up to approximately fifty (50) nautical miles.
An enhanced quantum well infrared photodetector is described in U.S. Pat. No. 5,539,206. This patent describes an infrared detector which includes a plurality of detector pixels, each of which comprises a plurality of elongate quantum well infrared radiation absorbing photoconductor elements. This photodetector, however, receives only one band of infrared radiation at one time.
The detectors which collect the desired radiation must be manufactured to be particularly sensitive for each of the desired radiation bands of interest. Such detectors are therefore complex and difficult to manufacture at a reasonable cost. The present invention is directed to an improved hyperspectral detector and system which can provide improved targeting and surveillance at long ranges, such as
50
nautical miles.
SUMMARY OF THE INVENTION
A selected embodiment of the present invention is a hyperspectral quantum well infrared radiation photodetector which includes an array of detectors, the array having an X-dimension (rows) and a Y-dimension (columns), wherein the detectors in each row have a common wavelength band of infrared radiation response and the detectors in each column have multiple wavelength bands of infrared radiation response. Each detector comprises a plurality of elongate, multiple quantum well infrared radiation absorbing elements, each element has a width dimension and, the center-to-center position of adjacent elements are separated by a pitch dimension. Each of the elements has first and second opposite longitudinal surfaces. The detectors in each of the columns have multiple width dimensions and multiple pitch dimensions to produce detectors having the multiple wavelength bands of infrared radiation response and the detectors in each of the rows have common width and pitch dimensions to produce a common wavelength band of infrared radiation response. The multiple quantum infrared elements comprise a diffraction grating for the infrared radiation. The first contact for each detector includes a plurality of planar electrically interconnected strips respectively in contact with and extending along the first surfaces of the multiple quantum well elements. A second contact for each detector is electrically connected to the second surfaces of the multiple quantum well elements. The first contact and the second contact for each detector are positioned on opposite longitudinal sides of each of the multiple quantum well elements to provide current flow through the elements in a direction substantially transversed to the axis of the elements. A planar reflector for the infrared radiation is positioned on an opposite side of the second contact from the multiple quantum well elements. The combined diffraction grating structure with the planar reflector and contact layers form a resonant optical cavity which captures the infrared radiation with the designated bandwidth.
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Claiborne Lewis T.
Gorin Brian Allen
Lewis, Jr. Henry Garton
Hardy David
Lockheed Martin Corporation
Sadacca Stephen S.
Sidley & Austin
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