Enhanced quantum efficiency barrier infrared detectors
Barrier infrared detectors having structures configured to enhance the quantum efficiency, and methods of their manufacture are provided. In particular, device structures for constructing high-performance barrier infrared detectors using novel combinations of p-type and n-type absorber regions and contact regions are provided. The infrared detectors generally incorporate a “p + Bpnn + ” structure. The detectors generally comprise, in sequence, a highly p-doped contact layer “p + ”, an electron unipolar barrier “B”, a p-type absorber section “p”, and n-type absorber section “n”, and a highly n-doped contact layer “n + ”.
1. A detector structure comprising:
a first contact layer formed from a p-type doped material, and a second contact layer formed from an n-type doped material, wherein at least the second contact layer does not include a hole blocking structure;
a unipolar electron barrier having first and second sides, and wherein the first side is disposed adjacent the first contact layer; and
a multi-segment absorber structure formed from at least a first absorber and a second absorber, wherein the first absorber is formed from a p-type absorber material and is disposed adjacent the second side of the unipolar electron barrier, and wherein the second absorber is formed from an n-type absorber material and is disposed between the first absorber and the second contact layer;
wherein the second absorber is connected to the second contact layer either directly or by a transition region, wherein where a transition region is present the transition region is directly connected at a first side to the second contact layer and at a second side to the second absorber; and
wherein the valence band edges of the unipolar electron barrier and multi-segment absorber structure are configured to minimize offset therebetween.
2. The detector structure of claim 1 , further comprising at least one transition region being disposed between at least two individual segments of the detector selected from the group consisting of the first contact layer and the unipolar electron barrier, the unipolar electron barrier and the first absorber, the first absorber and the second absorber, and the second absorber and the second contact layer; and
wherein the at least one transition region is configured to minimize offset between the band edges of the individual segments of the detector, and is formed of one of the graded-gap region, a graded-doping region, or a mixture thereof.
3. The detector structure of claim 2 , further comprising at least one graded-gap transition region being disposed between one of, or both, the unipolar electron barrier and the first absorber to minimize offset between their valence band edges, and the second absorber and the second contact layer to minimize offset between their conduction band edges.
4. The detector structure of claim 2 , wherein the graded-gap comprises a superlattice formed from a plurality of repeated layers of at least two semiconductor materials, each layer being defined by a layer thickness such that each superlattice has a period defined by the combined thicknesses of the plurality of repeated layers; and
wherein the energy band structure of each superlattice including the band gap, conduction band edge and the valence band edge depends on the composition, thickness and period of the plurality of the repeated layers.
5. The detector structure of claim 1 , wherein the at least first and second absorbers are formed from bulk semiconductors, type-II superlattice materials, or a mixture thereof.
6. The detector structure of claim 1 , wherein the unipolar electron barrier is graded-gap material.
7. The detector structure of claim 1 , wherein the unipolar electron barrier is ungraded and further comprising at least one graded-gap transition region being disposed between the unipolar electron barrier and the first absorber, and configured to minimize offset between the valence band edges of the absorber and the unipolar electron barrier.
8. The detector structure of claim 1 , wherein the second absorber is formed from a graded-gap material.
9. The detector structure of claim 1 , wherein the first contact layer is the top contact and the second contact layer is the bottom contact.
10. The detector structure of claim 1 , wherein the first contact layer is the bottom contact and the second contact layer is the top contact.
11. The detector structure of claim 1 , wherein the band gaps of the contact layers, the first absorber, and the second absorber are the same.
12. The detector structure of claim 1 , wherein the band gaps of the contact layers, the first absorber, and the second absorber are different.
13. The detector structure of claim 1 , wherein the band gaps of the contact layers are wider than the band gaps of the first and second absorbers.
14. A detector array comprising:
a two-dimensional array of detector structures comprising:
a first contact layer formed from a p-type doped material, and a second contact layer formed from an n-type doped material, wherein at least the second contact layer does not include a hole blocking structure,
a unipolar electron barrier having first and second sides, and wherein the first side is disposed adjacent the first contact layer, and
a multi-segment absorber structure formed from at least a first absorber and a second absorber, wherein the first absorber is formed from a p-type absorber material and is disposed adjacent the second side of the unipolar electron barrier, and wherein the second absorber is formed from an n-type absorber material and is disposed between the first absorber and the second contact layer,
wherein the second absorber is connected to the second contact layer either directly or by a transition region, wherein where a transition region is present the transition region is directly connected at a first side to the second contact layer and at a second side to the second absorber; and
wherein the valence band edges of the unipolar electron barrier and multi-segment absorber structure are configured to minimize offset therebetween; and
wherein the detector structures are mesa-isolated.
15. The detector array of claim 14 , wherein the first contact layer is the top contact, and wherein the individual detector structures are mesa-isolated by etching through the first contact layer, the unipolar electron barrier and the first absorber.
16. The detector array of claim 14 , wherein the second contact layer is the top contact, and wherein the individual detector structures are mesa-isolated by etching through at least the second contact layer and the second absorber.
17. The detector array of claim 14 , wherein the second contact layer is the top contact, and wherein the individual detector structures are mesa-isolated by etching through the second contact layer, the second absorber and the first absorber, and at least partially through the unipolar electron barrier.