Low-noise semiconductor photodetectors
View Patent ↗A photodetector is formed from a body of semiconductor material substantially surrounded by dielectric surfaces. A passivation process is applied to at least one surface to reduce the rate of carrier generation and recombination on that surface. Photocurrent is read out from at least one electrical contact, which is formed on a doped region whose surface lies entirely on a passivated surface. Unwanted leakage current from un-passivated surfaces is reduced through one of the following methods: (a) The un-passivated surface is separated from the photo-collecting contact by at least two junctions; (b) The un-passivated surface is doped to a very high level, at least equal to the conduction band or valence band density of states of the semiconductor; (c) An accumulation or inversion layer is formed on the un-passivated surface by the application of an electric field.
1. A method of detecting light, comprising:
using a semiconductor structure as a photodetector to detect incident light and generate an electrical signal representative of the detected incident light, the semiconductor structure comprising:
a body of semiconductor material having a surface comprising a first portion and a second portion;
a layer of a first dielectric material being configured to contact the first portion of the surface of the body of semiconductor material;
a second dielectric material contacting the second portion of the surface of the body of semiconductor material and configured to passivate the second portion;
wherein the body of semiconductor material comprises:
a first region doped to a first type of conductivity (p or n); and
a second region peripherally around the first region doped to a second type of conductivity (n or p) opposite the first type of conductivity, the second region forming a p-n junction with the first region, the p-n junction intersecting the surface of the body of semiconductor material at the second portion of the surface;
a plurality of ohmic contacts comprising a first ohmic contact to the first region and a second ohmic contact to the second region; and
a highly doped semiconductor material substantially surrounding the layer of the first dielectric material,
wherein the layer of the first dielectric material has a thickness configured to cause formation of an accumulation layer or an inversion layer at the first portion of the surface of the body of semiconductor material.
2. The method of claim 1 , wherein the highly doped semiconductor material substantially surrounding the layer of the first dielectric material is doped to the second type of conductivity, and wherein the thickness of the layer of the first dielectric material is configured to cause formation of an accumulation layer at the first portion of the surface of the body of semiconductor material.
3. The method of claim 2 , wherein the second region of the body of semiconductor material comprises a contact region doped to the second type of conductivity and configured to contact the accumulation layer, and wherein the second ohmic contact to the second region contacts the contact region of the second region.
4. The method of claim 1 , wherein the highly doped semiconductor material substantially surrounding the layer of the first dielectric material is doped to the first type of conductivity, and wherein the thickness of the layer of the first dielectric material is configured to cause formation of an inversion layer at the first portion of the surface of the body of semiconductor material.
5. The method of claim 1 , wherein the body of semiconductor material comprises germanium.
6. The method of claim 5 , wherein the body of semiconductor material comprises at least 80% germanium.
7. A method of detecting light, comprising:
using a semiconductor structure as a photodetector to detect incident light on a light receiving surface of the semiconductor structure and generate an electrical signal representative of the detected incident light, the semiconductor structure comprising:
a body of semiconductor material comprising:
an outer region doped to a first type of conductivity (p or n);
an inner region doped to a second type of conductivity (n or p) opposite the first type of conductivity;
a contact region in contact with the outer region, the contact region being highly doped to the first type of conductivity and comprising an exposed surface; and
a p-n junction formed between the outer region and the inner region; and
a plurality of metal contacts comprising a first metal contact to the contact region and a second metal contact to the inner region, the first metal contact and second metal contact being substantially co-planar within a plane substantially parallel to the light receiving surface of the semiconductor structure;
wherein less than approximately 30% of the exposed surface of the contact region is covered by metal contacts.
8. The method of claim 7 , wherein less than approximately 25% of the exposed surface of the contact region is covered by metal contacts.
9. The method of claim 7 , wherein the body of semiconductor material comprises germanium.
10. The method of claim 9 , wherein the body of semiconductor material comprises at least 80% germanium.