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. A method of making an infrared detector, the method comprising:
forming a bottom contact layer on a substrate;
forming a first mercury-cadmium telluride layer on the bottom contact layer, the 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;
forming a second mercury-cadmium telluride layer on the first mercury-cadmium telluride layer, the 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
forming a collector layer on the second mercury-cadmium telluride layer, the 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 layer having a third bandgap energy value that is less than the first bandgap energy value of the first mercury-cadmium telluride layer.
2. The method of claim 1 , further comprising pattern etching portions of at least the collector layer and second mercury-cadmium telluride layer to define two or more detector elements with side walls.
3. The method of claim 2 , wherein pattern etching further etches at least a portion of the first mercury-cadmium telluride layer.
4. The method of claim 2 , further comprising forming a passivation layer on the side walls.
5. The method of claim 4 , wherein forming a passivation layer comprises oxidizing the side walls.
6. The method of claim 1 , further comprising forming a top collector pad on the second major surface of the collector layer, the top collector pad comprising one or more metallization layers.
7. The method of claim 1 , further comprising forming a bottom conductive pad on the bottom contact layer, the bottom conductive pad comprising one or more metallization layers.
8. The method of claim 1 , wherein the third mercury-cadmium telluride layer has a cadmium mole faction with respect to mercury that is equal to or less than 0.13.
9. The method of claim 1 , wherein the substrate comprises at least one of the following materials: silicon, InSb, GaAs, or Ge.
10. The method of claim 1 , 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.
11. The method 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 15 dopant atoms per cubic centimeter.
12. The method 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 method 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.
14. The method 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.
15. The method of claim 1 , wherein the second mercury-cadmium telluride layer further comprises 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.