Multiquantum well structures for suppression of electron leakage and reduction of threshold-current density in quantum cascade lasers
Semiconductor structures for laser devices are provided. The semiconductor structures have a quantum cascade laser structure comprising an electron injector, an active region, and an electron extractor. The active region comprises an injection barrier, a multiquantum well structure, and an exit barrier. The multiquantum well structure can comprise a first barrier, a first quantum well, a second barrier, a second quantum well, and a third barrier. The energies of the first and second barrier are less than the energy of the third barrier. The energy difference between the energy of the second barrier and the energy of the third barrier can be greater than 150 meV and the ratio of the energy of the third barrier to the energy of the second barrier can be greater than 1.26.
1. A semiconductor structure comprising:
an electron injector, an active region adjacent to the electron injector, and an electron extractor adjacent to the active region, the electron injector, active region, and electron extractor each comprising layers of semiconductor, the layers configured to provide alternating quantum wells and barriers,
wherein the active region comprises an injection barrier, an exit barrier and a multiquantum well structure between the injection barrier and the exit barrier, the multiquantum well structure comprising
a first barrier,
a first quantum well adjacent to the first barrier,
a second barrier adjacent to the first quantum well,
a second quantum well adjacent to the second barrier, and
a third barrier adjacent to the second quantum well,
wherein the energies of the first barrier and the second barrier are less than the energy of the third barrier, the energy difference between the energy of the second barrier and the energy of the third barrier is greater than 225 meV and the ratio of the energy of the third barrier to the energy of the second barrier is greater than 1.26.
2. The semiconductor structure of claim 1 , wherein the energy difference between the energy of the second barrier and the energy of the third barrier is greater than 350 meV and the ratio of the energy of the third barrier to the energy of the second barrier is greater than 1.40.
3. The semiconductor structure of claim 1 , wherein the energy of the first barrier is substantially the same as the energy of the second barrier.
4. The semiconductor structure of claim 1 , wherein the energy of at least one of the first barrier and the second barrier is equal to or less than the energy of the barriers of the electron injector.
5. The semiconductor structure of claim 1 , wherein the energy of the third barrier is greater than the energy of the exit barrier.
6. The semiconductor structure of claim 1 , wherein the energy of the first barrier is substantially the same as the energy of the second barrier, the energy of the third barrier is greater than the energy of the exit barrier, and the energy of the third barrier and the energy of the exit barrier are greater than the energy of the barriers of the electron injector.
7. The semiconductor structure of claim 6 , wherein the energy of at least one of the first barrier and the second barrier is less than the energy of the barriers of the electron injector.
8. The semiconductor structure of claim 6 , wherein the energy of at least one of the first barrier and the second barrier is greater than the energy of the barriers of the electron injector.
9. The semiconductor structure of claim 1 , wherein the first quantum well of the multiquantum well structure and the second quantum well of the multiquantum well structure are deep quantum wells.
10. The semiconductor structure of claim 1 , wherein all of the quantum wells of the active region are deep quantum wells.
11. The semiconductor structure of claim 1 , wherein the semiconductor structure is configured to provide a laser device emitting radiation in the wavelength range of about 3.5 μm to about 5 μm.
12. A laser device comprising a plurality of laser stages, each laser stage comprising the semiconductor structure of claim 1 .
13. A semiconductor structure comprising:
an electron injector, an active region adjacent to the electron injector, and an electron extractor adjacent to the active region, the electron injector, active region, and electron extractor each comprising layers of semiconductor, the layers configured to provide alternating quantum wells and barriers,
wherein the active region comprises an injection barrier, an exit barrier and a multiquantum well structure between the injection barrier and the exit barrier, the multiquantum well structure comprising
a first barrier,
a first quantum well adjacent to the first barrier,
a second barrier adjacent to the first quantum well,
a second quantum well adjacent to the second barrier, and
a third barrier adjacent to the second quantum well,
wherein the energies of the first barrier and the second barrier are less than the energy of the third barrier, the energy difference between the energy of the second barrier and the energy of the third barrier is greater than 150 meV and the ratio of the energy of the third barrier to the energy of the second barrier is greater than 1.26, and further wherein the semiconductor structure is configured to provide a laser device emitting at a wavelength greater than about 5 μm.
14. The semiconductor structure of claim 13 , wherein the energy of the first barrier is substantially the same as the energy of the second barrier, the energies of the third barrier and the exit barrier are greater than the energy of the barriers of the electron injector, and the energy of the third barrier is substantially the same as the energy of the exit barrier.
15. The semiconductor structure of claim 14 , wherein the energy of at least one of the first barrier and the second barrier is greater than the energy of the barriers of the electron injector.
16. The semiconductor structure of claim 13 , wherein the semiconductor structure is configured to provide a laser device emitting at a wavelength of about 8 μm or greater.
17. A laser device comprising a plurality of laser stages, each laser stage comprising the semiconductor structure of claim 13 .
18. A semiconductor structure comprising:
an electron injector, an active region adjacent to the electron injector, and an electron extractor adjacent to the active region, the electron injector, active region, and electron extractor each comprising layers of semiconductor, the layers configured to provide alternating quantum wells and barriers,
wherein the active region comprises an injection barrier, an exit barrier and a multiquantum well structure between the injection barrier and the exit barrier, the multiquantum well structure comprising
a first barrier,
a first quantum well adjacent to the first barrier,
a second barrier adjacent to the first quantum well,
a second quantum well adjacent to the second barrier, and
a third barrier adjacent to the second quantum well,
wherein the energies of the first barrier and the second barrier are less than the energy of the third barrier, the energy of at least one of the first barrier and the second barrier is equal to or less than the energy of the barriers of the electron injector, and the energy of the third barrier is greater than the energy of the barriers of the electron injector.
19. The semiconductor structure of claim 18 , wherein the energy of the first barrier is substantially the same as the energy of the second barrier.
20. The semiconductor structure of claim 19 , wherein the energy of the third barrier is greater than the energy of the exit barrier.
21. A semiconductor structure comprising:
an electron injector, an active region adjacent to the electron injector, and an electron extractor adjacent to the active region, the electron injector, active region, and electron extractor each comprising layers of semiconductor, the layers configured to provide alternating quantum wells and barriers,
wherein the active region comprises an injection barrier, an exit barrier and a multiquantum well structure between the injection barrier and the exit barrier, the multiquantum well structure comprising
a first barrier,
a first quantum well adjacent to the first barrier,
a second barrier adjacent to the first quantum well, and
a second quantum well adjacent to the second barrier,
wherein the energies of the first barrier and the second barrier are less than the energy of the exit barrier, the energy difference between the energy of the second barrier and the energy of the exit barrier is greater than 225 meV and the ratio of the energy of the exit barrier to the energy of the second barrier is greater than 1.26.
22. The semiconductor structure of claim 21 , wherein the energy difference between the energy of the second barrier and the energy of the exit barrier is greater than 350 meV and the ratio of the energy of the exit barrier to the energy of the second barrier is greater than 1.40.
23. The semiconductor structure of claim 21 , wherein the energy of the first barrier is substantially the same as the energy of the second barrier.
24. The semiconductor structure of claim 21 , wherein the energy of at least one of the first barrier and the second barrier is greater than the energy of the barriers of the electron injector.
25. The semiconductor structure of claim 21 , wherein all of the quantum wells of the active region are deep quantum wells.