Room temperature, low-light-level visible imager
First Claim
1. A high-sensitivity photodetector for detecting radiation in the visible or shorter wavelength regions of the spectrum, suitable for room-temperature operation, comprising:
- a compound semiconductor photodiode which generates a detector current in response to incident photons, said photodiode biased below its avalanche breakdown threshold, comprising III-V elemental components and having a bandgap with transition energy higher than the energy of infrared photons;
a high trans-impedance interface circuit, arranged to receive a signal from said photodiode junction and amplify said signal, wherein said photodiode junction is integrated on a first substrate and said interface circuit is on a second substrate.
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Abstract
A photodetector sensitive to visible and shorter wavelengths is capable of single photon sensitivity at room temperatures and video frame rates. It includes (a) a compound semiconductor photodiode, biased below its avalanche breakdown threshold, comprising III-V elemental components and having a bandgap with transition energy higher than the energy of infrared photons; and (b) a high trans-impedance interface circuit, arranged to receive a signal from the photodiode junction and to amplify said signal. Preferably, the photodiode junction is integrated in a first microstructure on a first substrate, and its interface circuit in a second microstructure on a second substrate. Both microstructures are then joined in a laminar, sandwich-like structure and communicate via electrically conducting contacts.
58 Citations
28 Claims
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1. A high-sensitivity photodetector for detecting radiation in the visible or shorter wavelength regions of the spectrum, suitable for room-temperature operation, comprising:
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a compound semiconductor photodiode which generates a detector current in response to incident photons, said photodiode biased below its avalanche breakdown threshold, comprising III-V elemental components and having a bandgap with transition energy higher than the energy of infrared photons;
a high trans-impedance interface circuit, arranged to receive a signal from said photodiode junction and amplify said signal, wherein said photodiode junction is integrated on a first substrate and said interface circuit is on a second substrate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
and wherein said first and second microstructures communicate via electrically conducting contacts. -
3. The photodetector of claim 2, wherein electrically conducting contacts comprise indium.
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4. The photodetector of claim 3, wherein said interface circuit comprises:
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a load FET, having a source arranged to receive a small signal from said photodiode; and
an amplifier that is connected in a negative feedback loop around said load FET'"'"'s gate-to-source voltage.
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5. The photodetector of claim 4, wherein said interface circuit further comprises:
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a sampling circuit that samples the output of said amplifier, said sampling circuit comprising;
a capacitor that integrates the amplifier output;
an access switch which is clocked at a sampling frequency to read said output; and
a reset switch to discharge said capacitor after said voltage is read.
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6. The photodetector of claim 1, wherein said bandgap is at least 1.77 electron volts.
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7. The photodetector of claim 1, wherein said bandgap is at least 1.98 electron volts.
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8. The photodetector of claim 1, wherein said bandgap is at least 2.07 electron volts.
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9. The photodetector of claim 1, wherein said bandgap is at least 2.25 electron volts.
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10. The photodetector of claim 1, wherein said photodiode comprises:
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a detector layer comprising aluminum gallium arsenide; and
a substrate layer comprising gallium arsenide.
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11. The photodetector of claim 1, wherein said photodiode comprises:
a detector layer comprising aluminum indium gallium arsenide, and a substrate layer comprising indium phosphide.
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12. The photodetector of claim 1, wherein said photodiode comprises:
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a detector layer comprising gallium phosphide; and
a substrate layer comprising indium phosphide.
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13. The photodetector of claim 1, wherein said photodiode comprises:
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a detector layer comprising indium gallium nitride; and
a substrate layer comprising sapphire.
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14. An imaging array for use at room temperatures to detect images from low-level visible, ultraviolet or shorter illumination, suitable for use at video frame rates, comprising:
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a plurality of addressable photodetecting cells, each said cell comprising;
a compound semiconductor photodiode which generates a detector current in response to incident photons, said photodiode biased below its avalanche breakdown threshold, comprising III-V elemental components and having a bandgap with transition energy higher than the energy of infrared photons;
a high trans-impedance interface circuit, arranged to receive a signal from said photodiode junction and amplify said signal, wherein said photodiode is integrated on a first substrate and said interface circuit is on a second substrate. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
and wherein said first and second microstructures communicate via electrically conducting contacts. -
16. The imaging array of claim 14, wherein said electrically conducting contacts comprise indium.
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17. The imaging array of claim 14, wherein said interface circuit comprises:
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a load FET, having a source arranged to receive a small signal from said photodiode; and
an amplifier that is connected in a negative feedback loop around said load FET'"'"'s gate-to-source voltage.
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18. The imaging array of claim 14, wherein said interface circuit further comprises:
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a sampling circuit that samples the output of said amplifier, said sampling circuit comprising;
a capacitor that integrates the amplifier output;
an access switch which is clocked at a sampling frequency to read said output; and
a reset switch that is clocked at said sampling frequency to discharge said capacitor after said voltage is read.
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19. The imaging array of claim 14, wherein said bandgap is at least 1.77 electron volts.
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20. The imaging array of claim 14, wherein said bandgap is at least 1.98 electron volts.
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21. The imaging array of claim 14, wherein said bandgap is at least 2.07 electron volts.
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22. The imaging array of claim 14, wherein said bandgap is at least 2.25 electron volts.
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23. The imaging array of claim 14, wherein said photodiode comprises:
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a detector layer comprising aluminum gallium arsenide; and
a substrate layer comprising gallium arsenide.
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24. The imaging array of claim 14, wherein said photodiode comprises:
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a detector layer comprising aluminum indium gallium arsenide, and a substrate layer comprising indium phosphide.
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25. The imaging array of claim 14, wherein said photodiode comprises:
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a detector layer comprising gallium phosphide; and
a substrate layer comprising indium phosphide.
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26. The imaging array of claim 14, wherein said photodiode comprises:
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a detector layer comprising indium gallium nitride; and
a substrate layer comprising sapphire.
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27. The imaging array of claim 14, wherein the respective interface circuits of said cells have variable gain.
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28. The imaging array of claim 27, wherein the gain of said respective interface circuits is variably set in a manner complementary to a non-uniformity in a response of respective photodiodes of said cells.
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Specification