Infrared photodetectors

1. An infrared photodetector comprising:

a p-type and highly doped silicon substrate;

a metal structure disposed on the silicon substrate,

wherein the metal structure is a grating structure;

a first electric contact to the silicon substrate; and

a second electric contact to the metal structure.

2. The infrared photodetector according to claim 1 , wherein

the metal structure has an optical resonance in an infrared spectral region,

the doping density of the silicon substrate is high enough such that the resistivity of the silicon substrate changes due to free-carrier absorption in the silicon substrate.

3. The infrared photodetector according to claim 1 , wherein the crystal orientation of the silicon substrate is <100>.

4. The infrared photodetector according to claim 1 , wherein the resistivity of the silicon substrate is equal or greater than 0.001 and equal or less than 0.1 Ω·cm.

5. The infrared photodetector according to claim 1 , wherein the resistivity of the silicon substrate is equal or greater than 0.005 and equal or less than 0.05 Ω·cm.

6. The infrared photodetector according to claim 1 , wherein the resistivity of the silicon substrate is equal or greater than 0.01 and equal or less than 0.02 Ω·cm.

7. The infrared photodetector according to claim 1 , wherein the metal structure is aluminum.

8. The infrared photodetector according to claim 1 , wherein the metal structure comprises a gold layer disposed on a titanium layer.

9. The infrared photodetector according to claim 1 , wherein the metal structure is disposed directly on the silicon substrate and that creates an ohmic contact with the silicon substrate.

10. The infrared photodetector according to claim 1 , further comprising:

a power source that is connected to the first and second electrical contacts;

an infrared light source that emits light on the metal structure; and

a polarizer that polarizes light emitted from the light source.

11. The infrared photodetector according to claim 10 , further comprising optical elements that focus the emitted light on the metal structure.

12. An infrared spectrometer comprising:

a plurality of the infrared photodetectors according to claim 1 ; and

an infrared light source.

13. The infrared spectrometer according to claim 12 , further comprising optical elements that focus infrared light of the light source on the infrared photodetectors.

14. A method of measuring an absorbance spectrum of a material, the method comprising:

emitting infrared light on a plurality of infrared photodetectors such that the infrared light transmits through the material before reaching the infrared photodetectors;

measuring an electrical signal of each of the infrared photodetectors generated in response to absorption of the infrared light by the infrared photodetectors; and

calculating the absorption spectrum of the material based on the electrical signals of the infrared photodetectors and responsivities of the infrared photodetectors,

wherein the responsivity of each of the photodetectors is an electrical signal spectrum of the infrared photodetector divided by an infrared light spectrum that is received by the infrared detector and results into generating the electrical signal spectrum,

wherein each infrared photodetector comprises a metal structure disposed on a silicon substrate, and

wherein the metal structure is a grating structure.