Metal-contact-free photodetector
View Patent ↗A Ge-on-Si photodetector constructed without doping or contacting Germanium by metal is described. Despite the simplified fabrication process, the device has responsivity of 1.24 A/W, corresponding to 99.2% quantum efficiency. Dark current is 40 nA at −4 V reverse bias. 3-dB bandwidth is 30 GHz.
1. A photodetector, comprising:
a substrate including a device layer on a surface thereof;
a first doped semiconductor contact supported by the device layer;
a second doped semiconductor contact on the device layer;
a semiconductor body, in electrical contact with the first doped semiconductor contact and the second doped semiconductor contact, the semiconductor body capable of generating electrical signals by absorbing electromagnetic radiation;
a first metal terminal, in electrical communication with said first doped semiconductor contact, but lacking direct contact with the semiconductor body; and
a second metal terminal, in electrical communication with said second doped semiconductor contact, but lacking direct contact with the semiconductor body;
wherein the first and second metal terminals are configured to provide the electrical signals to external circuitry;
wherein said first doped semiconductor contact comprises a first portion underneath the semiconductor body, and a connecting slab between the semiconductor body and the first terminal; and
wherein the connecting slab comprises a higher doping level than the first portion.
2. The photodetector according to claim 1 , wherein at least one of said first doped semiconductor contact and said second doped semiconductor contact comprises a doped silicon contact.
3. The photodetector according to claim 1 , wherein the semiconductor body comprises germanium.
4. The photodetector according to claim 1 , wherein the semiconductor body comprises intrinsic germanium.
5. The photodetector according to claim 1 , wherein said first doped semiconductor contact comprises a p-type contact; and wherein said second doped semiconductor contact comprises an n-type contact.
6. The photodetector according to claim 1 , wherein said first doped semiconductor contact further comprises a second portion underneath the first terminal; and wherein the connecting slab comprises a doping level intermediate the first and second portions.
7. The photodetector according to claim 6 , wherein sheet resistance of the second portion is an order of magnitude smaller than that of the connecting slab.
8. The photodetector according to claim 1 , further comprising a third doped semiconductor contact.
9. The photodetector according to claim 1 , wherein said semiconductor body comprises a plurality of facets providing a non-planar faceted shape.
10. The photodetector according to claim 9 , wherein said semiconductor body comprises a triangular cross section.
11. The photodetector according to claim 10 , wherein one of the facets is oriented at an angle between 15° and 75° to an upper surface of the substrate.
12. A method of fabricating a semiconductor photodetector, comprising:
patterning an upper layer of a semiconductor wafer by lithography;
etching the upper layer to create waveguide portions and contact portions on a substrate;
doping the contact portions by implantation;
annealing the contact portions to form a p-type contact and an n-type contact;
performing epitaxial deposition to provide a semiconductor body in contact with the n-type contact and the p-type contact; and
applying metallization to form first and second contact terminals in electrical communication with the p-type contact and the n-type contact, respectively, but lacking direct contact with the semiconductor body;
wherein said etching step comprises etching a first portion of the p-type contact underneath the semiconductor body, and a connecting slab of the p-type contact between the semiconductor body and the first terminal; and
wherein the doping step comprising doping the connecting slab with a higher doping level than the first portion.
13. The method according to claim 12 , wherein the semiconductor body comprises intrinsic germanium.
14. The method according to claim 12 , wherein said epitaxy step comprises forming a plurality of facets providing a non-planar faceted shape.
15. The method according to claim 14 , wherein the epitaxy step includes mechanically or chemical-mechanical polishing the semiconductor body.
16. The method according to claim 14 , wherein the non-planar faceted shape comprises a triangular cross section.
17. The method according to claim 16 , wherein said epitaxy step comprises forming one of the facets to be oriented at an angle between 15° and 75° to an upper surface of the substrate.
18. The method according to claim 12 , wherein the etching step further comprises etching a second portion of the p-type contact underneath the first terminal; and wherein the doping step comprises doping the connecting slab to a level intermediate the first and second portions.