Avalanche photodetectors and image sensors including the same
A photodetector having a small form factor and having high detection efficiency with respect to both visible light and infrared rays may include a first electrode, a collector layer on the first electrode, a tunnel barrier layer on the collector layer, a graphene layer on the tunnel barrier layer, an emitter layer on the graphene layer, and a second electrode on the emitter layer. The photodetector may be included in an image sensor. An image sensor may include a substrate, an insulating layer on the substrate, and a plurality of photodetectors on the insulating layer. The photodetectors may be aligned with each other in a direction extending parallel or perpendicular to a top surface of the insulating layer. The photodetector may be included in a LiDAR system.
1. A photodetector, comprising:
a first electrode;
a collector layer on the first electrode;
a tunnel barrier layer on the collector layer;
a graphene layer on the tunnel barrier layer;
an emitter layer on the graphene layer; and
a second electrode on the emitter layer, the second electrode including a transparent conductive material,
wherein the collector layer includes a first semiconductor material and the emitter layer includes a second semiconductor material,
wherein at least one semiconductor material of the first semiconductor material and the second semiconductor material includes a transition metal dichalcogenide that is compound of a transition metal and a chalcogen element that is one of S, Se, or Te,
wherein the emitter layer has a thickness of about 0.3 nm to about 1 μm such that the emitter absorbs light and moves electrons and holes, and
wherein the tunnel barrier layer has a thickness of about 0.3 nm to about 1 μm.
2. The photodetector of claim 1 , wherein the first electrode at least partially includes a conductive metal material.
3. The photodetector of claim 1 , wherein the transition metal dichalcogenide includes at least one selected from a group consisting of MoS 2 , WS 2 , TaS 2 , HfS 2 , ReS 2 , TiS 2 , NbS 2 , SnS 2 , MoSe 2 , WSe 2 , TaSe 2 , HfSe 2 , ReSe 2 , TiSe 2 , NbSe 2 , SnSe 2 , MoTe 2 , WTe 2 , TaTe 2 , HfTe 2 , ReTe 2 , TiTe 2 , NbTe 2 , and SnTe 2 .
4. The photodetector of claim 1 , wherein the tunnel barrier layer includes an insulating material, the insulating material having a thickness that is at least a minimum thickness of the insulating material associated with tunneling of electrons and holes in the tunnel barrier layer.
5. The photodetector of claim 4 , wherein the tunnel barrier layer includes at least one material selected from a group consisting of SiO 2 and SiN.
6. The photodetector of claim 1 , wherein
the graphene layer includes single-layer graphene or multi-layer graphene, and
the graphene layer has a thickness of about 0.3 nm to about 1 μm.
7. An image sensor, comprising:
a substrate;
an insulating layer on the substrate;
a first photodetector on the insulating layer, the first photodetector including the photodetector of claim 1 , such that
the insulating layer is between the substrate and a first electrode of the first photodetector, and
the first electrode of the first photodetector is between the insulating layer and a collector layer of the first photodetector; and
a second photodetector on the first photodetector,
wherein the second photodetector includes
a separate collector layer,
a separate tunnel barrier layer on the separate collector layer,
a separate graphene layer on the separate tunnel barrier layer,
a separate emitter layer on the separate graphene layer, and
a separate second electrode on the separate emitter layer.
8. The image sensor of claim 7 , wherein
respective collector layers and emitter layers of the first photodetector and the second photodetector each include a semiconductor material.
9. The image sensor of claim 8 , wherein
respective emitter layers of the first photodetector and second photodetector include semiconductor materials having different band gaps.
10. An image sensor, comprising:
a substrate;
an insulating layer on the substrate; and
a first photodetector and a second photodetector separately on the insulating layer and aligned with each other in a direction that is parallel to a top surface of the insulating layer,
wherein each photodetector of the first and second photodetectors includes the photodetector of claim 1 , such that
the insulating layer is between the substrate and respective first electrodes of the first and second photodetectors, and
the first electrodes of the first and second photodetectors are between the insulating layer and respective collector layers of the first and second photodetectors.
11. The image sensor of claim 10 , wherein respective collector layers and respective emitter layers of the first photodetector and the second photodetector each include a semiconductor material.
12. The image sensor of claim 10 , wherein respective emitter layers of the first photodetector and the second photodetector include semiconductor materials having different band gaps.
13. An image sensor, comprising:
a substrate;
an insulating layer on the substrate; and
a first photodetector and a second photodetector on the insulating layer, at least one photodetector of the first and second photodetectors including the photodetector of claim 1 , such that
the insulating layer is between the substrate and a first electrode of the at least one photodetector, and
the first electrode of the at least one photodetector is between the insulating layer and a collector layer of the at least one photodetector.
14. The image sensor of claim 13 , wherein
the first photodetector and the second photodetector are separately on the insulating layer and aligned with each other on the insulating layer in a first direction that is parallel to a top surface of the insulating layer, and
the image sensor further includes a third photodetector and a fourth photodetector on the insulating layer, the third photodetector and the fourth photodetector aligned with each other on the insulating layer in a second direction that is perpendicular to the top surface of the insulating layer.
15. The image sensor of claim 13 , wherein respective collector layers and respective emitter layers of the first photodetector and the second photodetector each include a semiconductor material.
16. The image sensor of claim 13 , wherein respective emitter layers of the first photodetector and the second photodetector include semiconductor materials having different band gaps.
17. The photodetector of claim 1 , wherein an energy of the tunnel barrier layer in a conduction band is higher than an energy of the collector layer and an energy of the emitter layer in a conduction band.
18. The photodetector of claim 1 , wherein the emitter layer is configured to absorb light and generate electron-hole pairs.