Sub-pixel nBn detector
A method of making a two-dimensional detector array (and of such an array) comprising, for each of a plurality of rows and a plurality of columns of individual detectors, forming an n-doped semiconductor photo absorbing layer, forming a barrier layer comprising one or more of AlSb, AlAsSb, AlGaAsSb, AlPSb, AlGaPSb, and HgZnTe, and forming an n-doped semiconductor contact area.
1. A photodetector comprising
a photo absorbing layer having a predetermined doping type,
a contact layer having the predetermined doping type where said contact layer includes a plurality of contact regions, each contact region having an active area and a guard area, said guard and active areas being physically distinct; and
a barrier layer disposed between said photo absorbing and contact layers,
wherein each contact region has a physically distinct guard area; and
wherein a guard area for a first contact region is electrically connected to a second guard area of one or more adjacent contact regions by a resistor.
2. The detector of claim 1 wherein at least one semiconductor alloy is disposed at an interface of said barrier layer and at least one of said photo absorbing layer and said contact layer and where said at least one alloy is graded such that a graded band edge transition is created at said interface.
3. The photodetector of claim 1 , where the predetermined doping type is n-type.
4. The photodetector of claim 1 , where the barrier layer is un-doped.
5. The photodetector of claim 1 , where the guard areas include ohmic metal that is supplied with a reverse bias voltage.
6. The photodetector of claim 1 , where the first and second guard areas are supplied with a bias voltage.
7. The detector of claim 1 wherein said absorbing layer includes an absorber alloy having a chemical potential therein to drive minority carriers from the photo absorbing layer into the barrier layer.
8. The detector of claim 1 wherein said absorbing layer includes an absorber alloy and where the composition of the absorber alloy is graded.
9. The detector of claim 1 , where the barrier layer is graded with a first grading at a first interface area between said barrier and said contact layer and graded with a second grading at a second interface area between said barrier and said photo absorbing layer such that
the first grading creates a graded transition from the minority carrier band edge of the barrier layer to the minority carrier band edge of the contact layer; and
the second grading creates a graded transition from the minority carrier band edge of the photo absorbing layer to the minority carrier band edge of the barrier layer.
10. The detector of claim 1 , where the barrier layer is graded with a grading at an interface area between said barrier and said contact layer such that the grading creates a graded transition from the minority carrier band edge of the barrier layer to the minority carrier band edge of the contact layer.
11. The detector of claim 1 , where the barrier layer is graded with a grading at a an interface area between said barrier and said photo absorbing layer such that the grading creates a graded transition from the minority carrier band edge of the photo absorbing layer to the minority carrier band edge of the barrier layer.
12. The detector of claim 1 , where the bather layer is graded with a grading that creates a graded transition from the minority carrier band edge of the barrier layer to the minority carrier band edge of the photo absorbing layer.
13. The detector of claim 1 wherein said absorbing layer includes an absorber alloy and where the composition of the absorber alloy is graded such that a chemical potential is created in the alloy to drive minority carriers from the photo absorbing layer into the barrier layer.
14. The detector of claim 13 wherein said chemical potential reduces lateral diffusion of minority carriers within said absorber layer.
15. The detector of claim 1 additionally comprising:
a substrate disposed on said photo absorbing layer; and
a diffusion barrier portion; said diffusion barrier being disposed at an interface of said photo absorbing layer and said substrate.
16. The detector of claim 15 , where the diffusion barrier includes at least a first and a second strained superlattice buffer layer, the first and second strained superlattice buffer layers having different alloy compositions.
17. The detector of claim 1 additionally comprising
a substrate layer;
and an aluminum-bearing buffer layer disposed between said photo absorbing layer and said substrate;
wherein Al content of said buffer layer is graded.
18. The detector of claim 17 , where the Al content of the buffer layer is graded by including, in said buffer layer, at least a first and a second strained superlattice buffer layer, the first and second strained superlattice buffer layers having different Al content levels.
19. The detector of claim 1 , where the barrier layer is graded with a first grading that creates a graded transition from the minority carrier band edge of the barrier layer to the minority carrier band edge of the contact layer.
20. The detector of claim 19 , where the barrier layer is graded with a second grading that creates a graded transition from the minority carrier band edge of the photo absorbing layer to the minority carrier band edge of the barrier layer.
21. The detector of claim 1 , wherein the barrier layer includes at least one concentration gradient.
22. The detector of claim 21 , where the contact, absorber, and barrier layers each have a conduction band for minority carriers; and
where said at least one concentration gradient of the barrier layer is configured such that the minority carrier conduction bands of the barrier and absorber layers are aligned and the minority carrier conduction bands of the barrier and contact layers are aligned.
23. The detector of claim 1 additionally comprising a light concentrator disposed above said photo absorbing layer.
24. The detector of claim 23 wherein the light concentrator comprises a microlens.
25. The detector of claim 24 wherein the microlens is incorporated into a close proximity filter.
26. A photodetector comprising:
a photo absorbing layer having a predetermined doping type,
a contact layer having the predetermined doping type, and
a barrier layer disposed between said photo absorbing and contact layers;
where photo absorbing layer includes an absorber alloy and where the composition of the absorber alloy is graded in a way that creates a chemical potential in the alloy to drive minority carriers from the photo absorbing layer into the barrier layer,
where the barrier layer is graded with a first grading at a first interface area between said barrier and said contact layer and graded with a second grading at a second interface area between said barrier and said photo absorbing layer such that
the first grading creates a gradual transition from the minority carrier band edge of the barrier layer to the minority carrier band edge of the contact layer; and
the second grading creates a gradual transition from the minority carrier band edge of the photo absorbing layer to the minority carrier band edge of the barrier layer.
27. The photodetector of claim 26 , where the chemical potential reduces lateral diffusion of minority carriers through the photo absorbing layer.
28. The photodetector of claim 26 , where the graded absorber alloy and the second grading create the second interface.
29. The photodetector of claim 26 , where the graded absorber alloy is graded by varying Al content in the absorber alloy.
30. The photodetector of claim 26 , where the barrier layer is un-doped.
31. The photodetector of claim 26 , where the predetermined doping type is n-type.
32. The photodetector of claim 26 , where the contact layer includes a plurality of contact regions, each contact region representing a pixel.
33. The detector of claim 26 additionally comprising:
a substrate disposed on said photo absorbing layer; and
a diffusion barrier portion; said diffusion barrier being disposed at an interface of said photo absorbing layer and said substrate.
34. The detector of claim 33 , where the diffusion barrier includes at least a first and a second strained superlattice buffer layer, the first and second strained superlattice buffer layers having different alloy compositions.
35. The detector of claim 26 additionally comprising
a substrate layer;
and an aluminum-bearing buffer layer disposed between said photo absorbing layer and said substrate;
wherein Al content of said buffer layer is graded.
36. The detector of claim 35 , where the Al content of the buffer layer is graded by including, in said buffer layer, at least a first and a second strained superlattice buffer layer, the first and second strained superlattice buffer layers having different Al content levels.