Silicon-based photodetectors with expanded bandwidth
A hot carrier photodetector has been developed that absorbs approximately 80% of broadband infrared radiation by using a planar nanoscale back metal contact to silicon. Based on the principles of the hot carriers generation in ultrathin metal films, silicon-based CMOS image sensors are developed which operate in the IR diapason. The device uses absorption in an ultrathin metallic nanostructure to generate therein a non-equilibrium electron distribution which subsequently is injected into the silicon material via a Schottky contact at the Si body, thus generating a photoresponse to an incident IR radiation. A pixeled array including interconnected hot carriers metallic nanostructured cell(s) and traditional RGB elements is envisioned to enable RGB-IR imaging from a single silicon based wafer.
1. Si-based photodetecting system operating in a bandwidth expanded into Infrared (IR) diapason, comprising:
at least one IR photodetecting cell manufactured with:
a Si (silicon) substrate having a first surface and a second surface opposite to said first surface, wherein said silicon has a Si energy bandgap;
a Schottky contact formed on said second surface of said Si substrate, said Schottky contact including a thin conductive film having a nanometer scale thickness h and formed in substantially contiguous contact with said second surface of said Si substrate, thereby creating an energetic barrier having a height qΦ B between said Si substrate and said thin conductive film; and
an anti-reflection coating formed on said first surface of said Si substrate, and an ohmic contact formed on at least a portion of said first surface of said Si substrate;
wherein, upon illumination of said first surface of said Si substrate with a radiation having an in air wavelength κ 0 and having photons energy below said Si energy bandgap, said radiation passes through said Si substrate in a direction towards said second surface thereof, is absorbed in said thin conductive film of said Schottky contact, and excites hot carriers having an excitation energy exceeding said barrier height qΦ B , and wherein said hot carriers are injected in said Si substrate through said barrier, thus creating a photoresponse to said incident radiation.
2. The Si-based photodetecting system of claim 1 , further including at least first and second electrical connections, each coupled to a respective one of said ohmic contact and said thin conducting film, wherein said photoresponse is obtained between said first and second electrical connections.
3. The Si-based photodetecting system of claim 1 , wherein said thin conducting film has a refractive index m=n+ik, wherein n≈κ>>0, and wherein n and k are real and imaginary parts of the refractive index m, respectively.
4. The Si-based photodetecting system of claim 1 , wherein said thin conducting film is formed from a material including at least one of Pt, Fe, Cr, Ti, Cu, Al, Ni, Au, and alloys thereof.
5. The Si-based photodetecting system of claim 1 , wherein said anti-reflection coating is formed from a dielectric material having a refractive index smaller than a refractive index of Si.
6. The Si-based photodetecting system of claim 1 , wherein said thickness h of said thin film is shorter than said wavelength λ 0 of said incident radiation, h<<λ 0 /2π.
7. The Si-based photodetecting system of claim 1 , wherein said thickness h of said thin conductive film falls in a nanometer range.
8. The Si-based phoodetecting system of claim 1 , wherein the wavelength λ 0 of the incident radiation falls in the IR diapason, said wavelength λ 0 exceeding 1.1 μm.
9. The Si-based photodetecting system of claim 1 , wherein said Schottky contact barrier height qΦ B is tuned to control said photoresponse.
10. The Si-based photodetecting system of claim 9 , wherein said Schottky contact barrier height qΦ B is reduced by heavily doping said Si substrate in proximity to said thin conductive film.
11. The Si-based photodetecting system of claim 9 , wherein said Schottky contact barrier height qΦ B is tuned by applying an external bias voltage thereto.
12. The Si-based photodetecting system of claim 1 , wherein said Si substrate is an n-type Si.
13. The Si-based photodetecting system of claim 1 , wherein said photodetecting system includes a Si-based Complementary Metal-Oxide-Semiconductor (CMOS) image sensor formed with at least one said IR photodetecting cell.
14. The Si-based photodetecting system of claim 13 , wherein said Si-based CMOS image sensor includes a CMOS chip incorporating said at least one IR photodetecting cell and red-green-blue (RGB) elements operatively interconnected therebetween in a pixel array.
15. The Si-based photodetecting system of claim 1 , wherein said at least one of said second surface of said Si substrate and said thin conducting film in said at least one IR photodetecting cell is patterned to form a periodical nanostructure, including at least one of conducting microwires, microcones, metallic grating, metallic nanodisk array, 3-D nanostructures, and combinations thereof, said periodical nanostructure including said thin conductive film.
16. The Si-based photodetecting system of claim 1 , wherein said second surface of said Si substrate is substantially flat, and wherein said thin conductive film is an unpatterned film.