Photodetectors exploiting electrostatic trapping and percolation transport
This disclosure provides systems, methods, and apparatus related to photodetectors. In one aspect, a photodetector device comprises a substrate, a polycrystalline layer disposed on the substrate, and a first electrode and a second electrode disposed on the polycrystalline layer. The polycrystalline layer comprises nanograins with grain boundaries between the nanograins. The nanograins comprise a semiconductor material. A doping element comprising a halogen is segregated at the grain boundaries. A length of the polycrystalline layer is between and separating the first electrode and the second electrode.
1. A method comprising:
(a) fabricating a plurality nanocrystals, the plurality of nanocrystals comprising a semiconductor material, and each nanocrystal of the plurality of nanocrystals having ligands disposed on a surface of the nanocrystal;
(b) exchanging at least some of the ligands on each nanocrystal of the plurality of nanocrystals with a doping element comprising a halogen;
(c) after operations (a) and (b), depositing the plurality of nanocrystals on a substrate;
(d) thermally annealing the plurality of nanocrystals to form a polycrystalline layer comprising nanograins; and
(e) depositing a first electrode and a second electrode on the polycrystalline layer, a length of the polycrystalline layer being between and separating the first electrode and the second electrode.
2. The method of claim 1 , wherein the doping element segregates to grain boundaries in the polycrystalline layer during operation (d).
3. The method of claim 1 , wherein the plurality of nanocrystals comprise a semiconductor material selected from a group consisting of a III-V semiconductor material and a II-VI semiconductor material.
4. The method of claim 1 , wherein the doping element comprises chlorine.
5. The method of claim 1 , wherein operation (d) is performed at about 150° C. to 800° C.
6. The method of claim 1 , wherein operation (d) is performed for about 1 second to 30 minutes.
7. The method of claim 1 , wherein operation (d) is performed in an inert atmosphere.
8. The method of claim 1 , wherein each of the nanograins has a largest dimension of about 10 nanometers to 200 nanometers.
9. The method of claim 1 , wherein the polycrystalline layer has a thickness of about 10 nanometers to 5 microns.
10. The method of claim 1 , wherein the length of the polycrystalline layer between the first electrode and the second electrode is about 50 nanometers to 1 millimeter.
11. A method comprising:
(a) fabricating a plurality nanocrystals, the plurality of nanocrystals comprising cadmium telluride (CdTe), and each nanocrystal of the plurality of nanocrystals having cadmium oleate ligands disposed on a surface of the nanocrystal;
(b) exchanging at least some of the cadmium oleate ligands on each nanocrystal of the plurality of nanocrystals with a doping element comprising chlorine;
(c) after operation (b), depositing the plurality of nanocrystals on a substrate;
(d) thermally annealing the plurality of nanocrystals to form a polycrystalline layer comprising nanograins, the chlorine segregating to grain boundaries in the polycrystalline layer during the thermal annealing; and
(e) depositing a first electrode and a second electrode on the polycrystalline layer, a length of the polycrystalline layer being between and separating the first electrode and the second electrode.
12. The method of claim 11 , wherein operation (b) comprises:
dispersing the plurality of nanocrystals in toluene;
adding tributylphosphine (TBP) to the plurality of nanocrystals dispersed in toluene; and
after adding the tributylphosphine, adding trimethylsilychloride (TMSCl) to the plurality of nanocrystals dispersed in toluene.
13. The method of claim 11 , further comprising:
after operation (d), removing the polycrystalline layer from the substrate; and
depositing the polycrystalline layer on a substrate of a photodetector device.
14. The method of claim 11 , further comprising:
after operation (a), purifying the plurality of nanocrystals by suspending the plurality of nanocrystals in a liquid and separating the plurality of nanocrystals from the liquid.
15. The method of claim 11 , wherein operation (d) is performed at about 350° C.
16. The method of claim 11 , wherein operation (d) is performed for about 30 seconds to 5 minutes.
17. The method of claim 11 , wherein operation (d) is performed in an argon atmosphere.
18. The method of claim 11 , wherein each of the nanograins has a largest dimension of about 50 nanometers to 75 nanometers.
19. The method of claim 11 , wherein the polycrystalline layer has a thickness of about 10 nanometers to 5 microns.
20. The method of claim 11 , wherein the length of the polycrystalline layer between the first electrode and the second electrode is about 50 nanometers to 1 millimeter.