# US 9,437,759 B2 · Germanium metal-contact-free near-IR photodetector

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- Number: US 9,437,759 B2
- Document ID: US9437759B2
- Status: Granted
- Kind: B2
- Application number: 14/644,122
- Filed: 2015-03-10
- Published: 2016-06-02
- Granted: 2016-09-06
- Earliest claimed: 2014-03-10
- Assignees: Coriant Advanced Technology, LLC
- Applicants: Coriant Advanced Technology, LLC
- Inventors: Thomas Baehr-Jones; Yi Zhang; Michael J. Hochberg; Ari Novack
- Web page: https://patentgrep.com/patent/US9437759B2

## CPC

- H10F 77/14: Shape of semiconductor bodies; Shapes, relative sizes or dispositions of semiconductor regions within semiconductor bodies
- H10F 30/223: the potential barrier being a PIN barrier
- H10F 30/225: the potential barrier working in avalanche mode, e.g. avalanche photodiodes
- H10F 39/024: {of coatings or optical elements}
- H10F 39/028: {performed after manufacture of the image sensors, e.g. annealing, gettering of impurities, short-circuit elimination or recrystallisation}
- H10F 39/184: {Infrared image sensors}
- H10F 39/812: {Arrangements for transferring the charges in the image sensor perpendicular to the imaging plane, e.g. buried regions used to transfer generated charges to circuitry under the photosensitive region}
- H10F 71/1212: {consisting of germanium}
- H10F 77/12: Active materials
- H10F 77/122: comprising only Group IV materials
- Y02E 10/547: Monocrystalline silicon PV cells
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

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.

## Claims

### Claim 1

A germanium photodetector, comprising:
a first doped semiconductor contact;
a second doped semiconductor contact; and
an intrinsic germanium body in electrical contact with said first doped semiconductor contact and in electrical contact with said second doped semiconductor contact, said first doped semiconductor contact and said second doped semiconductor contact disposed on a same side of said intrinsic germanium body, said intrinsic germanium body lacking direct mechanical contact with a metal contact;
said first doped semiconductor contact and said second doped semiconductor contact in electrical communication with respective metal terminals configured to provide electrical signals generated in the germanium photodetector by absorption of electromagnetic radiation to circuitry external to the germanium photodetector.

### Claim 2 (depends on 1)

The germanium photodetector of claim 1, wherein at least one of said first doped semiconductor contact and said second doped semiconductor contact is a doped silicon contact.

### Claim 3 (depends on 1)

The germanium photodetector of claim 1, wherein at least one of said first doped semiconductor contact and said second doped semiconductor contact is doped with a p-type dopant.

### Claim 4 (depends on 1)

The germanium photodetector of claim 1, wherein at least one of said first doped semiconductor contact and said second doped semiconductor contact is doped with an n-type dopant.

### Claim 5 (depends on 1)

The germanium photodetector of claim 1, further comprising a third doped semiconductor contact.

### Claim 6 (depends on 1)

The germanium photodetector of claim 1, wherein said intrinsic germanium body has a triangular cross section.

### Claim 7 (depends on 1)

The germanium photodetector of claim 1, wherein said intrinsic germanium body is terminated in a (111) crystallographic face.

### Claim 8 (depends on 1)

The germanium photodetector of claim 1, wherein said intrinsic germanium body is planaraized.

### Claim 9 (depends on 1)

The germanium photodetector of claim 1, wherein a crystallographic facet is oriented at an angle between substantially 15 degrees and 75 degrees to the surface of the silicon wafer.

### Claim 10 (depends on 1)

The germanium photodetector of claim 1, wherein a measured quantum efficiency is greater than substantially 65%.

### Claim 11 (depends on 1)

The germanium photodetector of claim 1, wherein a measured quantum efficiency is greater than substantially 75%.

### Claim 12 (depends on 1)

The germanium photodetector of claim 1, wherein a measured quantum efficiency is greater than substantially 85%.

### Claim 13 (depends on 1)

The germanium photodetector of claim 1, wherein a measured quantum efficiency is greater than substantially 95%.

### Claim 14 (depends on 1)

The germanium photodetector of claim 1, wherein the photodetector comprises a p-i-n junction.

### Claim 15 (depends on 1)

The germanium photodetector of claim 1, wherein said electromagnetic radiation is in the wavelength range of substantially 1280-1600 nm in free space.

### Claim 16

A method of detecting electromagnetic radiation with a germanium photodetector, comprising:
providing a germanium photodetector, comprising:
a first doped semiconductor contact;
a second doped semiconductor contact; and
an intrinsic germanium body in electrical contact with said first doped semiconductor contact and in electrical contact with said second doped semiconductor contact, said first doped semiconductor contact and said second doped semiconductor contact disposed on a same side of said intrinsic germanium body, said intrinsic germanium body lacking direct mechanical contact with a metal contact
said first doped semiconductor contact and said second doped semiconductor contact in electrical communication with respective metal terminals configured to provide electrical signals generated in the germanium photodetector by absorption of electromagnetic radiation to circuitry external to the germanium photodetector;
receiving electromagnetic radiation by said germanium photodetector;
generating electrical signals representative of an intensity of said electromagnetic radiation or representative of data encoded in said electromagnetic radiation; and
performing at least one of displaying said electrical signals to a user and recording said electrical signals in a machine-readable memory in non-volatile form.

### Claim 17 (depends on 16)

The method of detecting electromagnetic radiation of claim 16, wherein said germanium photodetector supports single optical mode operation.

### Claim 18 (depends on 16)

The germanium photodetector of claim 16, wherein said electromagnetic radiation is in the wavelength range of substantially 1280-1600 nm in free space.

### Claim 19 (depends on 16)

The method of detecting electromagnetic radiation of claim 16, wherein said germanium photodetector supports conduction mode operation.

### Claim 20 (depends on 16)

The method of detecting electromagnetic radiation of claim 16, wherein said germanium photodetector supports operation in avalanche photodiode mode.

### Claim 21

A method of fabricating a germanium photodetector, comprising:
patterning a silicon wafer having a surface by lithography and etching to create waveguides on the surface;
doping the silicon by implantation and annealing to form a p-type contact and an n-type contact in a layer at the surface of the silicon wafer;
performing germanium epitaxy to provide an intrinsic germanium body having no deliberately added dopant in contact with the n-type contact and the p-type contact, the germanium body having a shape bounded by crystallographic facets oriented at an angle to the surface of the silicon wafer; and
applying metallization to form contact terminals.

### Claim 22 (depends on 21)

The method of fabricating a germanium photodetector of claim 21, wherein the photodetector is sensitive to electromagnetic radiation is in the wavelength range of substantially 1280-1600 nm in free space.

### Claim 23 (depends on 21)

The method of fabricating a germanium photodetector of claim 21, wherein the photodetector includes a p-i-n junction.

### Claim 24 (depends on 21)

The method of fabricating a germanium photodetector of claim 21, wherein a crystallographic facet is oriented at an angle between substantially 15 degrees and 75 degrees to the surface of the silicon wafer.