Minority carrier based HgCdTe infrared detectors and arrays
View Patent ↗Disclosed are minority carrier based mercury-cadmium telluride (HgCdTe) infrared detectors and arrays, and methods of making, are disclosed. The constructions provided by the invention enable the detectors to be used at higher temperatures, and/or be implemented on less expensive semiconductor substrates to lower manufacturing costs. An exemplary embodiment a substrate, a bottom contact layer disposed on the substrate, a first mercury-cadmium telluride layer having a first bandgap energy value disposed on the bottom contact layer, a second mercury-cadmium telluride layer having a second bandgap energy value that is greater than the first bandgap energy value disposed on the first mercury-cadmium telluride layer, and a collector layer disposed on the second mercury-cadmium telluride layer, wherein the first and second mercury-cadmium telluride layers are each doped with an n-type dopant.
1. An infrared detector comprising:
a substrate;
a bottom contact layer disposed on the substrate;
a first mercury-cadmium telluride layer having a first major surface disposed on the bottom contact layer, a second major surface parallel to the first major surface, and a first bandgap energy value, the first mercury-cadmium telluride layer being doped with an n-type dopant;
a second mercury-cadmium telluride layer having a first major surface disposed on the second major surface of the first mercury-cadmium telluride layer, a second major surface parallel to the first major surface of the second mercury-cadmium telluride layer, and a second bandgap energy value that is greater than the first bandgap energy value, the second mercury-cadmium telluride layer being doped with an n-type dopant; and
a collector layer having a first major surface disposed on the second major surface of the second mercury-cadmium telluride layer, and a second major surface parallel to the first major surface of the collector layer, wherein the collector layer comprises a third mercury-cadmium telluride material having a third bandgap energy value that is less than the first bandgap energy value of the first mercury-cadmium telluride layer.
2. The infrared detector of claim 1 , wherein the first mercury-cadmium telluride layer further has at least one side wall disposed between the first and second major surfaces of the first mercury-cadmium telluride layer, wherein the second mercury-cadmium telluride layer further has at least one side wall disposed between the first and second major surfaces of the second mercury-cadmium telluride layer, and wherein the infrared detector further comprises a passivation layer disposed on the side walls of the first and second mercury-cadmium telluride layers.
3. The infrared detector of claim 2 , wherein the passivation layer comprises an oxide.
4. The infrared detector of claim 1 , wherein the third mercury-cadmium telluride material has a cadmium mole faction with respect to mercury that is equal to or less than 0.13.
5. The infrared detector of claim 1 , wherein the collector layer comprises a semi-metal material.
6. The infrared detector of claim 1 , wherein the third mercury-cadmium telluride material is mercury telluride.
7. The infrared detector of claim 1 , wherein the substrate comprises at least one of the following materials: silicon, InSb, GaAs, or Ge.
8. The infrared detector of claim 7 , wherein the first mercury-cadmium telluride layer is characterized by a surface area and comprises a concentration of crystal defects equal to or greater than 1×10 6 defects per square centimeter of the surface area.
9. The infrared detector of claim 1 , wherein the concentration of the n-type dopant within the first mercury-cadmium telluride layer is at or below a concentration level of 4×10 15 dopant atoms per cubic centimeter.
10. The infrared detector of claim 1 , wherein the concentration of the n-type dopant within the first mercury-cadmium telluride layer is at or below a concentration level of 1×10 15 dopant atoms per cubic centimeter.
11. The infrared detector of claim 1 , wherein the concentration of the n-type dopant within the first mercury-cadmium telluride layer is at or below a concentration level of 5×10 14 dopant atoms per cubic centimeter.
12. The infrared detector of claim 1 , wherein the first mercury-cadmium telluride layer has a bandgap energy value in the range of 0.24 eV to 0.27 eV and a Shockley-Read minority carrier lifetime that is equal to or greater than 100 μs.
13. The infrared detector of claim 12 , wherein the first mercury-cadmium telluride layer has a first n-type dopant level, and wherein the quantity formed by the square of the first n-type dopant level multiplied by the Shockley-Read minority carrier lifetime of the first mercury-cadmium telluride layer has a value that is in the range from 0.25*2n i 2 τ Ai1 to 4*2n i 2 τ Ai1 , where n i is the intrinsic carrier concentration of the first mercury-cadmium telluride layer, and τ Ai1 is the Auger1 lifetime at the operating temperature of the infrared detector.
14. The infrared detector of claim 12 , wherein the first mercury-cadmium telluride layer has a first n-type dopant level, and wherein the quantity formed by the square of the first n-type dopant level multiplied by the Shockley-Read minority carrier lifetime of the first mercury-cadmium telluride layer has a value that is in the range from 0.06*2n i 2 τ Ai1 to 16*2n i 2 τ Ai1 , where n i is the intrinsic carrier concentration of the first mercury-cadmium telluride layer, and τ Ai1 is the Auger1 lifetime at the operating temperature of the infrared detector.
15. The infrared detector of claim 1 , wherein the first mercury-cadmium telluride layer has a bandgap energy value in the range of 0.19 eV to 0.22 eV and a Shockley-Read minority carrier lifetime that is equal to or greater than 10 μs.
16. The infrared detector of claim 15 , wherein the first mercury-cadmium telluride layer has a first n-type dopant level, and wherein the quantity formed by the square of the first n-type dopant level multiplied by the Shockley-Read minority carrier lifetime of the first mercury-cadmium telluride layer has a value that is in the range from 0.25*2n i 2 τ Ai1 to 4*2n i 2 τ Ai1 , where n i is the intrinsic carrier concentration of the first mercury-cadmium telluride layer, and τ Ai1 is the Auger1 lifetime at the operating temperature of the infrared detector.
17. The infrared detector of claim 15 , wherein the first mercury-cadmium telluride layer has a first n-type dopant level, and wherein the quantity formed by the square of the first n-type dopant level multiplied by the Shockley-Read minority carrier lifetime of the first mercury-cadmium telluride layer has a value that is in the range from 0.06*2n i 2 τ Ai1 to 16*2n i 2 τ Ai1 , where n i is the intrinsic carrier concentration of the first mercury-cadmium telluride layer, and τ Ai1 is the Auger1 lifetime at the operating temperature of the infrared detector.
18. The infrared detector of claim 1 , wherein the first mercury-cadmium telluride layer has a first n-type dopant level, a first thickness, and a bandgap energy value E G,A , wherein the quantity formed by the square of the first thickness multiplied by the first n-type dopant level is equal to or less than the quantity 2·∈ A ·∈ o ·E G,A /q, where ∈ o is the permitivity in vacuum, ∈ A is the relative permittivity of the first mercury-cadmium telluride layer with respect to vacuum, and q is the electron charge.
19. The infrared device of claim 1 , wherein the first mercury-cadmium telluride layer is configured as a first absorbing layer for a first range of infrared radiation when a bias of a first polarity is applied to the infrared device and the second mercury-cadmium telluride layer is configured as a second absorbing layer for a second range of infrared radiation when a bias of a second polarity is applied to the infrared device.
20. The infrared device of claim 19 , wherein the second mercury-cadmium telluride layer further has a graded composition of cadmium that causes the second bandgap energy to have values that vary along a dimension spanning between the first and second major surfaces of the second mercury-cadmium telluride layer.