Per-pixel performance improvement for combined visible and infrared image sensor arrays
A per-pixel performance improvement is described for combined image sensor arrays that measure infrared and visible light. One embodiment is a method that includes forming an array of photodetectors on a silicon substrate, treating a subset of the photodetectors to improve sensitivity to infrared light, and finishing the photodetector array to form an image sensor.
1. An image sensor comprising:
a silicon substrate;
a first set of photodetectors on the silicon substrate that have impurities that improve sensitivity to infrared light;
a second set of photodetector on the silicon substrate, that do not have the impurities; and
an optical system to direct visible and infrared light to the first and the second sets of photodetectors.
2. The image sensor of claim 1 , wherein the impurities comprise at least one of sulfur, selenium, and tellurium.
3. The image sensor of claim 1 , wherein the impurities are trapped in the silicon matrix of photodetectors of the first array of photodetectors.
4. The image sensor of claim 1 , wherein the array is formed on a back side of the silicon substrate.
5. The image sensor of claim 4 , further comprising circuit layers on a front side of the silicon substrate opposite the circuit layers.
6. The image sensor of claim 1 , further comprising:
a plurality of infrared light color filters one over each photodetector of the first set of photodetectors; and
a plurality of visible light color filters one over each photodetector of the second set of photodetectors.
7. The image sensor of claim 6 , wherein the visible light color filters are in a repeating pattern over the array.
8. A portable computing system comprising:
a processor;
a communications chip coupled to the processor to send and receive images; and
an image sensor coupled to the processor having a silicon substrate, a first set of photodetectors on the silicon substrate that have impurities that improve sensitivity to infrared light a second set of photodetector on the silicon substrate, that do not have the impurities, and an optical system to direct visible and infrared light to the first and the second sets of photodetectors.
9. The system of claim 8 , wherein the first set of photodetectors is doped with the impurities.
10. The system of claim 8 , wherein the first set of photodetectors has a reduced effective silicon band gap as compared to the second set of photodetectors.
11. The system of claim 8 , wherein the first set of photodetectors is distributed across the sensor in a repeating pattern with the second set of photodetectors.