Photodetector focal plane arrays with enhanced detection capability
A photodetector focal plane array (FPA) with enhanced detection capability and reduced thermal current is provided. The FPA includes light-concentrating dielectric structures in a form of arrays of elements with three-dimensional geometrical shapes. The elements have tapered sidewalls that taper inwardly toward a surface portion with a reduced width. A photodetector is joined to the portion with a reduced width. A metallic layer is disposed over the tapered sidewalls of the elements and the portion of the surface of the elements with a reduced width. The metallic layer provides mirror reflection properties to concentrate electromagnetic fields towards the detectors. The photodetector focal plane array may be used for infrared (IR) imaging applications in mid-wave IR (MWIR) and long-wave IR (LWIR) cameras as night vision and thermal imaging devices.
1 . A photodetector focal plane array (FPA) comprising:
a) photodetectors that are photosensitive in the IR region of the electromagnetic spectrum;
b) light-concentrating dielectric structures in a form of arrays comprising elements with three-dimensional geometrical shapes, wherein the elements have a first surface, a second surface, and tapered sidewalls that taper inwardly to a portion of said second surface that has a reduced width, wherein a detector is joined to the portion that has a reduced width; and
c) a metallic layer that is disposed over the tapered sidewalls of the elements and the portion of the surface of the elements that has a reduced width and the detector, wherein the metallic layer provides mirror reflection properties to concentrate electromagnetic fields towards the detectors.
2 . The photodetector focal plane array (FPA) of claim 1 wherein the photodetector is photosensitive in at least one of the MWIR or LWIR regions of the electromagnetic spectrum.
3 . The photodetector focal plane array (FPA) of claim 1 wherein the detector is selected from the group consisting of: metal/silicide Schottky barrier photodetectors in the case of all-silicon structures, photoconductive mercury cadmium telluride (MTC), PbSe, InSb or other semiconductor thin films, quantum dot or superlattice type II detector structures.
4 . The photodetector focal plane array (FPA) of claim 1 wherein the elements with three-dimensional geometrical shapes are selected from the group consisting of: micropyramids, microcones, microspheres, microcubes, or microvoids.
5 . The photodetector focal plane array (FPA) of claim 1 wherein the elements with three-dimensional geometrical shapes are integrated with wafers containing layers with different index of refraction such for example as silicon-on-insulator (SOI) to provide additional resonant enhancement of the power absorbed by the detectors.
6 . The photodetector focal plane array (FPA) of claim 1 further comprising:
d) surface dielectric quarter-wavelength layers, wherein a first surface dielectric quarter-wavelength layer is disposed over the first surface of the elements, and a second surface dielectric quarter-wavelength layer is disposed over the second surface of the elements, wherein said second surface dielectric quarter-wavelength layer is positioned between the metallic layer and the second surface of the elements.
7 . The photodetector focal plane array (FPA) of claim 6 wherein the surface dielectric quarter-wavelength layers comprise silica layers.
8 . An imaging system comprising the photodetector focal plane array (FPA) of claim 1 that further comprises a readout integrated circuit (ROIC) electrically connected to individual photodetectors to provide a pixel-by-pixel image acquisition.
9 . A method for concentrating IR radiation in a dielectric structure, said method comprising:
1) providing a photodetector focal plane array (FPA) comprising:
a) photodetectors that are photosensitive in the IR region of the electromagnetic spectrum;
b) light-concentrating dielectric structures in a form of arrays comprising elements with three-dimensional geometrical shapes, wherein the elements have a first surface, a second surface, and tapered sidewalls that taper inwardly to a portion of said second surface that has a reduced width, wherein a photodetector is joined to the portion that has a reduced width; and
c) a metallic layer that is disposed over the tapered sidewalls of the elements and the portion of the surface of the elements that has a reduced width, wherein the metallic layer provides mirror reflection properties to concentrate electromagnetic fields towards the detectors; and
2) directing radiation into the interior of the tapered structure wherein at least some of the radiation reflects off at least one of the surfaces of the tapered side walls toward another surface of the tapered side walls.