Cross-talk suppression in Geiger-mode avalanche photodiodes
An avalanche photodiode detector is provided with a substrate including an array of avalanche photodiodes. An optical interface surface of the substrate is arranged for accepting external input radiation. There is provided at least one cross-talk blocking layer of material including apertures positioned to allow external input radiation to reach photodiodes and including material regions positioned for attenuating radiation in the substrate that is produced by photodiodes in the array. Alternatively at least one cross-talk blocking layer of material is disposed on the optical interface surface of the substrate to allow external input radiation to reach photodiodes and attenuate radiation in the substrate that is produced by photodiodes in the array. At least one cross-talk filter layer of material can be disposed in the substrate adjacent to the photodiode structures, including a material that absorbs radiation in the substrate that is produced by photodiodes in the array.
1. An avalanche photodiode detector comprising:
a substrate including an array of avalanche photodiodes;
an optical interface surface of said substrate arranged for accepting external input radiation; and
at least one cross-talk blocking layer of material comprising a continuous blanket layer of GaInAs, said continuous blanket layer of GaInAs including a pattern of apertures positioned in said continuous blanket layer of GaInAs to allow said external input radiation to reach said avalanche photodiodes in said substrate and including continuous material regions of said continuous blanket layer of GaInAs that are positioned for attenuating radiation in said substrate that is produced by said avalanche photodiodes in said array.
2. The avalanche photodiode detector of claim 1 further comprising a microlens array disposed at a position relative to the substrate to focus said external input radiation to said avalanche photodiodes.
3. The avalanche photodiode detector of claim 2 wherein the microlens array is adjacent to and separated from the substrate.
4. The avalanche photodiode detector of claim 1 further comprising connections from the substrate to photodiode control and readout circuitry.
5. The avalanche photodiode detector of claim 1 wherein the radiation produced by said avalanche photodiodes comprises photons emitted by an avalanche photodiode during a Geiger-mode avalanche event at that said avalanche photodiode.
6. The avalanche photodiode detector of claim 1 wherein the pattern of apertures in the continuous blanket layer of GaInAs comprises an array of circular apertures.
7. The avalanche photodiode detector of claim 1 wherein each of said avalanche photodiodes comprises a mesa structure of photodiode layers and the pattern of apertures in the continuous blanket layer of GaInAs allows input radiation to reach the mesa structures.
8. The avalanche photodiode detector of claim 7 wherein the mesa structures are disposed at a substrate surface opposite the optical interface surface of the substrate.
9. The avalanche photodiode detector of claim 1 wherein the substrate comprises a semiconducting substrate.
10. The avalanche photodiode detector of claim 9 wherein the substrate comprises an InP substrate.
11. The avalanche photodiode detector of claim 1 wherein the at least one cross-talk blocking layer of material is disposed in a bulk region of the substrate.
12. The avalanche photodiode detector of claim 11 wherein the at least one cross-talk blocking layer of material comprises a plurality of cross-talk blocking layers, each of the cross-talk blocking layers in the substrate being separated from other of the cross-talk blocking layers by substrate bulk regions.
13. The avalanche photodiode detector of claim 11 further comprising at least one cross-talk blocking surface layer disposed on the optical interface surface of the substrate.
14. The avalanche photodiode detector of claim 1 wherein each avalanche photodiode in said array of avalanche photodiodes comprises a structure of a semiconducting input radiation absorber layer and a semiconducting avalanche multiplier layer, and further comprising
at least one cross-talk spectral filter layer of material disposed in said substrate adjacent to said structure of said semiconducting input radiation absorber layer and said semiconducting avalanche multiplier layer and including a material that absorbs radiation in said substrate that is produced by said avalanche photodiodes in said array.
15. The avalanche photodiode detector of claim 14 wherein the cross-talk spectral filter layer is a semiconductor layer characterized by a band gap that corresponds to wavelengths of photons produced by photodiodes in the array.
16. The avalanche photodiode detector of claim 14 wherein each of said avalanche photodiodes in the array of avalanche photodiodes comprises a mesa structure including the semiconducting input radiation absorber layer and the semiconducting avalanche multiplier layer.
17. The avalanche photodiode detector of claim 14 wherein the cross-talk spectral filter layer is characterized by a semiconducting band gap corresponding to wavelengths of radiation produced at the avalanche multiplier layer of photodiodes in the array.
18. The avalanche photodiode detector of claim 14 wherein said semiconducting input radiation absorber layer is characterized by a semiconducting band gap corresponding to wavelengths of said external input radiation to be detected by the array of said avalanche photodiodes.
19. The avalanche photodiode detector of claim 14 wherein said semiconducting input radiation absorber layer is characterized by a semiconducting band gap that sets a long wavelength boundary on a pass band of radiation wavelengths to be detected by the array of said avalanche photodiodes and wherein the cross-talk spectral filter layer is characterized by a semiconducting band gap that sets a short wavelength boundary on a pass band of radiation wavelengths to be detected by the array of said avalanche photodiodes.
20. The avalanche photodiode detector of claim 14 wherein the substrate comprises InP and the cross-talk spectral filter layer comprises an InGaAsP alloy.
21. The avalanche photodiode detector of claim 20 wherein the semiconducting input radiation absorber layer comprises an InGaAsP alloy and wherein the semiconducting avalanche multiplier layer comprises InP.
22. The avalanche photodiode detector of claim 1 wherein each avalanche photodiode in the array of avalanche photodiodes comprises a semiconducting input radiation absorber layer and a semiconducting avalanche multiplier layer.
23. The avalanche photodiode detector of claim 14 wherein the cross-talk spectral filter layer is continuous across the array of said avalanche photodiodes.
24. The avalanche photodiode detector of claim 22 wherein the semiconducting input radiation absorber layer comprises InGaAsP and wherein the substrate and the semiconducting avalanche multiplier layer each comprises InP.
25. The avalanche photodiode detector of claim 22 wherein each of said avalanche photodiodes in the array of avalanche photodiodes comprises a mesa structure including the semiconducting input radiation absorber layer and the semiconducting avalanche multiplier layer.