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1. WO2011008979 - STRAIN -BALANCED EXTENDED -WAVELENGTH BARRIER PHOTODETECTOR

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[ EN ]

CLAIMS

What is claimed is:

1. A strain-balanced photodetector with an extended wavelength, comprising: a first layer grown on a semiconductor substrate;

a barrier layer located above the first layer; and

a second layer located above the barrier layer,

characterized in that the first layer comprises:

a plurality of photo-absorbing layers; and

a plurality of strain-compensating layers interspersed between the plurality of photo-absorbing layers,

wherein the photo-absorbing layers are grown substantially lattice-mismatched to the substrate, and the strain-compensating layers are interspersed between the photo-absorbing layers so as to substantially compensate for a mechanical strain of the photo-absorbing layers caused by the lattice-mismatched condition.

2. The photodetector of claim 1 , wherein the photo-absorbing layers are stacked in an alternating arrangement with the strain-compensating layers, with one of the strain-compensating layers being located between each pair of the photo-absorbing layers.

3. The photodetector of claim 1 , wherein the plurality of photo-absorbing layers are comprised of indium arsenide antimonide (InAsSb) or indium gallium arsenide (InGaAs); and the plurality of strain-compensating layers are comprised of gallium arsenide (GaAs) or indium antimonide (InSb).

4. The photodetector of claim 3, wherein the substrate is comprised of gallium antimonide (GaSb) or indium arsenide (InAs).

5. The photodetector of claim 1, wherein each of the plurality of strain-compensation layers has a thickness such that the strain-compensation layers are substantially quantum-mechanically transparent.

6. The photodetector of claim 1 , wherein the first layer has an aggregate thickness sufficient to exhibit photo-absorption with reasonable quantum efficiency while exhibiting an extended long cutoff frequency beyond that of a photodetector with a first layer that is grown lattice-matched to a substrate.

7. The photodetector of claim 1 , wherein the plurality of strain-compensating layers are interspersed between the plurality of photo-absorbing layers at a periodic interval such that the strain-compensation layers are substantially transparent to quantum waveforms.

8. The photodetector of claim 1, wherein

the first layer exhibits a valence band energy and a conducting band energy during operation of the photodetector;

the barrier layer has a band energy gap and associated conduction and valence band energies; and

the second layer exhibits a valence band energy and a conducting band energy during operation of the photodetector,

wherein the relationship between the first and second layer valence and conduction band energies and the barrier layer conduction and valance band energies facilitates minority carrier current flow while inhibiting majority carrier current flow between the first and second layers.

9. The photodetector of claim 1, wherein a portion of the second layer is etched down to the barrier layer to define a lateral extent of the photodetector.

10. The photodetector of claim 1 , wherein the second layer comprises individual sections which are delineated from each other in a direction across the photodetector, each section corresponding to an individual detector element,

wherein said barrier layer extends past the individual sections of the second layer in the direction across the photodetector, and is monolithically provided for each of the individual detector elements, thereby passivating the photodetector during operation by blocking the flow of majority carriers to exposed surfaces of said barrier layer.

11. The photodetector of claim 1 , wherein the second layer forms a mesa on the barrier layer such that the barrier layer laterally extends beyond the mesa thereby passivating the photodetector during operation by preventing majority carriers from flowing to exposed surfaces of said barrier layer.

12. The photodetector of claim 1, wherein the first and second layers have the same majority carrier type such that the photodetector has no substantial depletion layer.

13. The photodetector of claim 1 , wherein the barrier layer has a semiconductor alloy composition AlAsxSb i_x with x being selected to provide a valence band energy for the barrier layer which is substantially equal to the valence band energy of the plurality of photo-absorbing layers.

14. The photodetector of claim 1 , wherein the barrier layer comprises aluminum gallium arsenide antimonide (AlGaAsSb).

15. The photodetector of claim 14, wherein the AlGaAsSb barrier layer has a semiconductor alloy composition AlyGai-yAsxSbi-x with 0.5 < y < 1.0 and with 0 < x < 0.1 being selected to provide a valence band energy for the barrier layer which is substantially equal to the valence band energy of the plurality of photo-absorbing layers.

16. The photodetector of claim 1 , wherein the photo-absorbing layers comprise InAsxSbi_x with 0 < x < 0.9.

17. The photodetector of claim 16, wherein each photo-absorbing layer has a layer thickness of about 100 nanometers or less.

18. The photodetector of claim 16, wherein each strain-compensating layer has a layer thickness of 5 nanometers or less.

19. The photodetector of claim 1 , wherein a long cutoff wavelength of the photodetector is in a range of 4.5 to 10 μm at a temperature of 200 0K or less.

20. The photodetector of claim 1 , wherein the plurality of photo-absorbing layers comprise 10 to 2000 photo-absorbing layers.

21. The photodetector of claim 1 , wherein the first layer has a thickness in the range of 1 to 10 μm.

22. The photodetector of claim 1 , wherein the lattice constant of the photo-absorbing layers is larger than the substrate such that each photo- absorbing layer is compression-strained and each strain-compensating layer is tensile-strained.

23. The photodetector of claim 1 , wherein the lattice constant of the photo-absorbing layers is smaller than the substrate such that each photo-absorbing layer is tensile-strained and each strain-compensating layer is compression-strained.

24. The photodetector of claim 1, wherein the first and second layers exhibit substantially identical compositions.

25. The photodetector of claim 1, wherein the first and second layers are either both n-type or both p-type.

26. The photodetector of claim 1, wherein the barrier layer comprises a substantially undoped material.

27. The photodetector of claim 1, further comprising:

a first electrode electrically connected to the first layer; and

a second electrode electrically connected to the second layer.

28. A strain-balanced photodetector with an extended wavelength, comprising: a first layer grown on a semiconductor substrate;

a barrier layer located above the first layer; and

a second layer located above the barrier layer,

characterized in that the second layer comprises:

a plurality of photo-absorbing layers; and

a plurality of strain-compensating layers interspersed between the plurality of photo-absorbing layers, wherein

the photo-absorbing layers are grown substantially lattice-mismatched to the barrier layer, and the strain-compensating layers are interspersed between the photo-absorbing layers so as to substantially compensate for a mechanical strain of the photo-absorbing layers caused by the lattice-mismatched condition.

29. The photodetector of claim 28, wherein the lattice constant of the photo-absorbing layers is larger than the barrier layer such that each photo-absorbing layer is compression-strained and each strain-compensating layer is tensile-strained.

30. The photodetector of claim 28, wherein the lattice constant of the photo-absorbing layers is smaller than the barrier layer such that each photo-absorbing layer is tensile-strained and each strain-compensating layer is compression-strained.

31. The photodetector of claim 28, wherein the photo-absorbing layers are stacked in an alternating arrangement with the strain-compensating layers, with one of the strain-compensating layers being located between each pair of the photo-absorbing layers.

32. The photodetector of claim 28, wherein the plurality of photo-absorbing layers are comprised of indium arsenide antimonide (InAsSb) or indium gallium arsenide (InGaAs); and the plurality of strain-compensating layers are comprised of gallium arsenide (GaAs) or indium antimonide (InSb).

33. The photodetector of claim 32, wherein the substrate is comprised of gallium antimonide (GaSb) or indium arsenide (InAs).

34. The photodetector of claim 28, wherein each of the plurality of strain-compensation layers has a thickness such that the strain-compensation layers are substantially quantum-mechanically transparent.

35. The photodetector of claim 28, wherein the first layer has an aggregate thickness sufficient to exhibit photo-absorption with reasonable quantum efficiency while exhibiting an extended long cutoff frequency beyond that of a photodetector with a first layer that is grown lattice-matched to a substrate.

36. The photodetector of claim 28, wherein the plurality of strain-compensating layers are interspersed between the plurality of photo-absorbing layers at a periodic interval such that the strain-compensation layers are substantially transparent to quantum waveforms.

37. The photodetector of claim 28, wherein

the first layer exhibits a valence band energy and a conducting band energy during operation of the photodetector;

the barrier layer has a band energy gap and associated conduction and valence band energies; and

the second layer exhibits a valence band energy and a conducting band energy during operation of the photodetector,

wherein the relationship between the first and second layer valence and conduction band energies and the barrier layer conduction and valance band energies facilitates minority carrier current flow while inhibiting majority carrier current flow between the first and second layers.

38. The photodetector of claim 28, wherein a portion of the second layer is etched down to the barrier layer to define a lateral extent of the photodetector.

39. The photodetector of claim 28, wherein the second layer comprises individual sections which are separate from each other in a direction across the photodetector, each section corresponding to an individual detector element,

wherein said barrier layer extends past the individual sections of the second layer in the direction across the photodetector, and is monolithically provided for each of the individual detector elements, thereby passivating the photodetector during operation by blocking the flow of majority carriers to exposed surfaces of said barrier layer.

40. The photodetector of claim 28, wherein the second layer forms a mesa on the barrier layer such that the barrier layer laterally extends beyond the mesa thereby passivating the photodetector during operation by preventing majority carriers from flowing to exposed surfaces of said barrier layer.

41. The photodetector of claim 28, wherein the first and second layers have the same majority carrier type such that the photodetector has no substantial depletion layer.

42. The photodetector of claim 28, wherein the barrier layer has a semiconductor alloy composition AlAsxSbi-x with x being selected to provide a valence band energy for the barrier layer which is substantially equal to the valence band energy of the plurality of photo-absorbing layers.

43. The photodetector of claim 28, wherein the barrier layer comprises aluminum gallium arsenide antimonide (AlGaAsSb).

44. The photodetector of claim 28, wherein the first and second layers exhibit substantially identical compositions.

45. The photodetector of claim 28, wherein the first and second layers are either both n-type or both p-type.

46. The photodetector of claim 28, wherein the barrier layer comprises a substantially undoped material.

47. The photodetector of claim 28, further comprising:

a first electrode electrically connected to the first layer; and

a second electrode electrically connected to the second layer.

48. A majority carrier filter photodetector exhibiting an extended cutoff wavelength and a reduced dark current, comprising:

a first layer grown on a semiconductor substrate;

a barrier layer located above the first layer; and

a second layer located above the barrier layer,

characterized in that the first layer comprises a plurality of compressively strained photo-absorbing layers of indium arsenide antimonide (InAsSb) grown alternatingly with a plurality of strain-compensating layers of gallium arsenide (GaAs).

49. The photodetector of claim 48, wherein the semiconductor substrate is comprised of gallium antimonide (GaSb).

50. The photodetector of claim 48, wherein each InAsSb photo-absorbing layer comprises InAsxSbi-x with 0 < x < 0.9.

51. The photodetector of claim 48, wherein each GaAs layer has a thickness which is less than or equal to one-fifth of the thickness of an adjacent InAsSb layer.

52. The photodetector of claim 48, wherein the first layer has a total thickness in the range of 1 to 10 μm.

53. The photodetector of claim 48, wherein a long cutoff wavelength for the detection of light is in the range of 4.5 to 10 μm at a lemperature of 160 0K or less.

54. The photodetector of claim 48, wherein the first layer comprises 10 to 2000 pairs of alternating layers of InAsSb and GaAs.

55. The photodetector of claim 48, wherein the barrier layer comprises aluminum arsenide antimonide (AlAsSb).

56. The photodetector of claim 48, further comprising:

a first electrode electrically connected to the first layer; and

a second electrode electrically connected to the second layer.

57. A strain-balanced photodetector, comprising:

a first layer grown on a semiconductor substrate;

a barrier layer located above the first layer; and

a second layer located above the barrier layer,

characterized in that at least one of the first and second layers is grown substantially lattice-mismatched to the substrate and/or the barrier layer and comprises a plurality of strain-compensating layers interspersed between a plurality of photo-absorbing layers so as to substantially compensate for a mechanical strain of the photo-absorbing layers caused by the lattice-mismatched condition.

58. The photodetector of claim 57, further comprising:

a first electrode electrically connected to the first layer; and

a second electrode electrically connected to the second layer.

59. The photodetector of claim 57, wherein the photodetector comprises a two-color photodetector wherein the first layer exhibits a first cutoff wavelength and the second layer exhibits a second cutoff wavelength, and the first cutoff wavelength is shorter than the second cutoff wavelength.

60. The photodetector of claim 57, wherein the first layer comprises an alloy of InAsSb substantially lattice-matched to GaSb; and the second layer comprises a plurality of tensile-strained strain-compensating layers interspersed between a plurality of compressive-strained photo-absorbing layers comprised of InGaAsSb.

61. The photodetector of claim 57, wherein the first layer comprises a plurality of compressive-strained strain-compensating layers comprised of InAswSbi_w interspersed between a plurality of tensile-strained photo-absorbing layers comprised of InxGa] _xAsySbi_y; and the second layer comprises an alloy of InAsSb substantially lattice-matched to GaSb.

62. The photodetector of claim 57, wherein the first layer comprises a plurality of compressive-strained strain-compensating layers comprised of InAswSbi_w interspersed between a plurality of tensile strained photo-absorbing layers comprised of InxGa] -xAsySbi-y.

63. The photodetector of claim 57, wherein the first layer comprises a plurality of photo-absorbing layers comprised of InAsSb and a plurality of strain-compensating layers comprised of GaAs; and the second layer comprises a plurality of photo-absorbing layers comprised of InGaSb and a plurality of strain-compensating layers comprised of InSb.

64. The photodetector of claim 60, wherein the strain-compensating layers are comprised of GaAs.

65. The photodetector of claim 61 , wherein the strain-compensating layers are comprised of InSb.

66. The photodetector of claim 62, where the strain-compensating layers of the first layer are comprised of InSb; and the strain-compensating layers of the second layer are comprised of GaAs.

67. The photodetector of claim 57, wherein the substrate comprises GaSb or InAs; and the barrier layer comprises AlAsSb or AlGaAsSb.

68. The photodetector of claim 57, wherein the minority carrier bandedge of at least one of the first and second layers is graded vertically by varying the alloy composition in a direction toward the barrier layer, and wherein a plurality of varying strain-compensating layers are interspersed within said at least one of the first and second layers such that the lattice structure is substantially prevented from dislocating.

69. The photodetector of claim 68, wherein the interval between the strain-compensating layers is gradually varied in the direction toward the barrier layer in order to balance the varying strain within the at least one of the first and second layers.

70. The photodetector of claim 68, wherein the thickness of the strain-compensating layers is gradually varied in the direction toward the barrier layer in order to balance the varying strain within the at least one of the first and second layers.

71. The photodetector of claim 69, wherein the thickness of the strain-compensating layers is gradually varied in the direction toward the barrier layer in order to balance the varying strain within the at least one of the first and second layers.

72. The photodetector of claim 70, wherein the interval between the strain-compensating layers is gradually varied in the direction toward the barrier layer in order to balance the varying strain within the at least one of the first and second layers.

73. A focal plane array with an extended cutoff wavelength, characterized by: a plurality of photodetectors according to any of claims 1, 28, 48, and 57 arranged in a two-dimensional matrix.

74. A method of forming a strain-balanced extended- wavelength photodetector for a desired cutoff wavelength, characterized by:

determining a periodic interval at which to intersperse, within a photo-absorbing region, a plurality of strain-compensating layers such that the strain-compensating layers are substantially quantum-mechanically transparent while compensating for a mechanical strain of the photo-absorbing region on a substrate in a lattice-mismatched condition; and

growing the photodetector by alternatingly growing on the substrate a plurality of photo-absorbing layers of a first alloy and the plurality of strain-compensation layers of a second alloy at the determined periodic interval,

wherein the determining of the periodic interval comprises:

selecting a desired cutoff wavelength for the photodetector;

determining a mole fraction for the first alloy which corresponds to the desired cutoff wavelength;

determining, for the determined mole fraction, a layer thickness ratio between a thickness of the strain-compensation layers and the photo-absorbing layer sufficient to achieve strain balancing of the photo-absorbing layer;

selecting a value for the periodic interval for providing strain-compensation layers at the thickness corresponding to the layer thickness ratio such that the strain-compensation layers are substantially electrically transparent to minority carriers.