High operating temperature resonant tunnelling quantum well photodetector
An semiconductor structure comprises a first quantum well having a first state (E 3 ) with an energy that is greater than an energy of a lower state (E 1 ) by a first energy difference, a quantum well structure ( 100 ) adjacent to the first quantum well and having at least a second state (E 4 ) having an energy level which is resonant with the first state (E 3 ) of the first quantum well, a second quantum well having at least a third state (E 2 ) to collect electrons from the second state (E 4 ) of the quantum well structure through a non-radiative mechanism and a fourth state (E 5 ). An energy of the fourth state of the second quantum well is greater than an energy of the third state (E 2 ) by a second energy difference. The structure can absorb two photons, one in the first quantum well by excitation of a carrier from the lower energy state (E 1 ) to the first state (E 3 ) and another in the second quantum well by excitation of a carrier from the third state (E 2 ) to the fourth state (E 5 ). The quantum well structure provides efficient extraction of excited carriers from the first quantum well.
1. A quantum well semiconductor structure comprising
a first quantum well having at least a first state (E 3 ), an energy of the first state being greater than an energy of a lower energy state (E 1 ) by a first energy difference;
a quantum well structure adjacent to the first quantum well and having at least a second state (E 4 ) having an energy level which is resonant with the first state (E 3 ) of the first quantum well; and
a second quantum well within or adjacent to the quantum well structure, and having at least a third state (E 2 ) to collect electrons from the second state (E 4 ) of the quantum well structure through a non-radiative mechanism and a fourth state (E 5 ), an energy of the fourth state of the second quantum well being greater than an energy of the third state (E 2 ) by a second energy difference.
2. A semiconductor structure as claimed in claim 1 wherein an energy difference between an energy of the second state (E 4 ) of the quantum well structure and the energy of the third state (E 2 ) of the second quantum well is equal to or greater than an LO phonon energy in the quantum well structure.
3. A semiconductor structure as claimed in claim 1 wherein the first energy difference is equal or substantially equal to the second energy difference.
4. A semiconductor structure as claimed in claim 1 wherein the first energy difference and the second energy difference are different to one another.
5. A semiconductor structure as claimed in claim 1 wherein the first energy difference and the second energy difference correspond to photon energies in the infrared region of the spectrum.
6. A semiconductor structure as claimed in claim 1 wherein the first state (E 3 ) of the first quantum well comprises a plurality of states forming a miniband.
7. A semiconductor structure as claimed in claim 1 wherein the fourth state (E 5 ) of the second quantum well comprises a plurality of states forming a miniband.
8. A semiconductor structure as claimed in claim 1 wherein the quantum well structure is a multiple quantum well structure.
9. A semiconductor structure as claimed in claim 1 , wherein the lower energy state (E 1 ) is a ground state of the first quantum well.
10. A semiconductor structure as claimed in claim 1 , wherein the lower energy state (E 1 ) is in a valence band.
11. A semiconductor structure as claimed in claim 1 , wherein the third state (E 2 ) of the second quantum well is a ground state of the second quantum well.
12. An infrared photodetector comprising a semiconductor structure as defined in claim 1 .
13. A photodetector as claimed in claim 12 and further comprising a transistor for current amplification.
14. A photodetector as claimed in claim 12 and further comprising a transistor for high frequency electromagnetic generation.
15. A photodetector as claimed in claim 13 wherein the transistor is a monolithically integrated transistor.
16. An imaging array having one or more photodetectors as defined in claim 12 .
17. An infrared free space communication system having a receiver comprising a photodetector as defined in claim 12 .
18. A solar cell comprising a semiconductor structure as claimed in claim 1 .
19. A photodetector as claimed in claim 14 wherein the transistor is a monolithically integrated transistor.