Photodetection

1. An apparatus, comprising:

a semiconductor film; and

at least one semiconductor nanostructure comprising a heterojunction configured to modulate the conductivity of the semiconductor film by assisting photo-generated carriers to transfer into the semiconductor film from the at least one semiconductor nanostructure;

wherein the heterojunction assists photo-generated carriers to transfer into the semiconductor film by separating them in the at least one semiconductor nanostructure.

2. An apparatus as claimed in claim 1 , wherein the transfer of photo-generated carriers into the semiconductor film from the at least one semiconductor nanostructure generates an electric field which modulates the conductivity of the semiconductor film.

3. An apparatus as claimed in claim 1 wherein the heterojunction is a type-II heterojunction.

4. An apparatus as claimed in claim 1 , wherein the at least one semiconductor nanostructure comprises first and second semiconductor nanomaterials that form the heterojunction, wherein the first and second semiconductor nanomaterials are arranged relative to the semiconductor film such that photo-generated carriers are transferred from the second semiconductor nanomaterial to the semiconductor film, and not from the first semiconductor nanomaterial to the semiconductor film.

5. An apparatus as claimed in claim 4 , further comprising: an electrical bridge extending from the second semiconductor nanomaterial to the semiconductor film.

6. An apparatus as claimed in claim 5 , wherein the electrical bridge is or comprises a metal.

7. A method, comprising:

modulating the conductivity of a semiconductor film using a heterojunction of at least one semiconductor nanostructure; and

causing the heterojunction to assist photo-generated carriers to transfer into the semiconductor film from the at least one semiconductor nanostructure by separating the photo-generated carriers in the at least one semiconductor nanostructure.

8. An apparatus, comprising:

a semimetal film; and

at least one semiconductor nanostructure, comprising a heterojunction, configured to generate carrier pairs in the semimetal film via resonant energy transfer, and configured to generate an external electric field for separating the generated carrier pairs in the semimetal film.

9. An apparatus as claimed in claim 8 , wherein the heterojunction is a type-II heterojunction.

10. An apparatus as claimed in claim 8 , wherein the carrier pairs in the semimetal are generated via resonant energy transfer from photo-generated carrier pairs in the at least one semiconductor nanostructure.

11. An apparatus as claimed in claim 8 , wherein the heterojunction is configured to generate the external electric field by separating photo-generated carrier pairs.

12. An apparatus as claimed in claim 11 , further comprising a barrier between the at least one semiconductor nanostructure and the semiconductor film, wherein the external electric field is generated by separating the photo-generated carrier pairs bound within the at least one semiconductor nanostructure by the barrier.

13. An apparatus as claimed in claim 8 , wherein the at least one semiconductor nanostructure is configured to generate the external electric field by assisting photo-generated carriers to transfer into the semimetal film from the at least one semiconductor nanostructure.

14. An apparatus as claimed in claim 13 , wherein the heterojunction assists photo-generated carriers to transfer into the semiconductor film by separating them in the at least one semiconductor nanostructure.

15. An apparatus as claimed in claim 8 ,

further comprising at least one further semiconductor nanostructure, comprising a further heterojunction, configured to generate further carrier pairs in the semimetal film via resonant energy transfer, and configured to generate a further external electric field for separating the further generated carrier pairs in the semimetal film.

16. An apparatus as claimed in claim 15 , wherein the at least one semiconductor nanostructure is configured to generate carrier pairs in the semimetal film via resonant energy transfer from photo-generated carrier pairs generated in the at least one semiconductor nanostructure in response to reception of light having a frequency equal to or above a first frequency threshold.

17. An apparatus as claimed in claim 16 , wherein the at least one further semiconductor nanostructure is configured to generate further carrier pairs in the semimetal film via resonant energy transfer from photo-generated carrier pairs generated in the at least one further semiconductor nanostructure in response to reception of light having a frequency equal to or above a second frequency threshold, which is lower than the first frequency threshold.

18. An apparatus as claimed in claim 17 , wherein current in the semimetal film is produced in response to reception of light by the at least one semiconductor nanostructure and the at least one further semiconductor nanostructure having a frequency below the first frequency threshold and above or equal to the second frequency threshold, and no current in the semimetal is produced in response to reception of light by the at least one semiconductor nanostructure and the at least one further semiconductor nanostructure having a frequency equal to or above the first frequency threshold and below the second frequency threshold.

19. A method, comprising:

using at least one semiconductor nanostructure, comprising a heterojunction, to generate carrier pairs in a semimetal film via resonant energy transfer; and

using the heterojunction to generate an external electric field for separating the generated carrier pairs in the semimetal film.