Infrared detector using a resonant optical cavity for enhanced absorption
First Claim
1. A photodetector for detecting optical radiation in a band centered about a predetermined wavelength, comprising:
- a. an optical cavity having a metallic reflector at a first end thereof and being open to receive optical radiation at a second, opposite end thereof, the total optical distance between the first and second ends of the cavity being an odd multiple of one-quarter of said predetermined wavelength, such that when the first end of the cavity is optically irradiated with energy within said band by a source outside the cavity, optical standing waves are produced in the cavity with the optical field intensity of such standing waves varying with distance from the reflector and having at least one peak of intensity within the cavity;
b. a layer of semiconductor material, termed the "active layer", which is optically absorptive at said predetermined wavelength and which is disposed within the cavity at a location including a region of peak optical intensity; and
c. first and second electrodes electrically coupled to the active layer for connecting the detector to apparatus for sensing changes in the detector resulting from the incidence on the open end of the cavity of radiation in said band.
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Abstract
A photodetector for detecting optical irradiation at a predetermined wavelength is provided with an integral, resonant optical cavity by forming a plurality of layers of material on a metallic reflector backing, the total optical thickness of those layers being an odd multiple of one-quarter of the predetermined wavelength. One of those layers is an active (i.e. optically-absorptive) semiconductor material. When the materials are deposited, that absorbing layer is formed at a level in the cavity including a region of peak optical field. As a result of the enhanced absorption provided by the resonant structure, the active layer may be very thin (i.e., less than one-tenth of a wavelength thick), yielding many beneficial results.
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Citations
10 Claims
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1. A photodetector for detecting optical radiation in a band centered about a predetermined wavelength, comprising:
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a. an optical cavity having a metallic reflector at a first end thereof and being open to receive optical radiation at a second, opposite end thereof, the total optical distance between the first and second ends of the cavity being an odd multiple of one-quarter of said predetermined wavelength, such that when the first end of the cavity is optically irradiated with energy within said band by a source outside the cavity, optical standing waves are produced in the cavity with the optical field intensity of such standing waves varying with distance from the reflector and having at least one peak of intensity within the cavity; b. a layer of semiconductor material, termed the "active layer", which is optically absorptive at said predetermined wavelength and which is disposed within the cavity at a location including a region of peak optical intensity; and c. first and second electrodes electrically coupled to the active layer for connecting the detector to apparatus for sensing changes in the detector resulting from the incidence on the open end of the cavity of radiation in said band. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification