# US 7,612,340 B2 · Method of operating an avalanche photodiode for reducing gain normalized dark current

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- Number: US 7,612,340 B2
- Document ID: US7612340B2
- Status: Granted
- Kind: B2
- Application number: 11/196,100
- Filed: 2005-08-03
- Published: 2007-02-08
- Granted: 2009-11-03
- Earliest claimed: 2005-08-03
- Assignees: DRS Sensors & Targeting Systems, Inc.
- Inventors: Jeffrey Don Beck; Pradip Mitra; Chang-Feng Wan; Michael A. Kinch
- Web page: https://patentgrep.com/patent/US7612340B2

## CPC

- H10F 77/959: {for devices working in avalanche mode}
- H10F 30/2212: {the devices comprising active layers made of only Group II-VI materials, e.g. HgCdTe infrared photodiodes}
- 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 77/123: comprising only Group II-VI materials, e.g. CdS, ZnS or HgCdTe
- H10F 77/1237: {having at least three elements, e.g. HgCdTe}
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

An avalanche photodiode is operated in avalanche mode at a selected reverse bias that achieves high gain and a reduced gain normalized dark current.

## Claims

### Claim 1

A method of operating an avalanche photodiode in an avalanche gain mode for reducing dark current noise, wherein the photodiode has a gain normalized dark current, wherein the photodiode has sources of dark current that are dominant when a reverse bias below an avalanche gain threshold voltage is applied to the photodiode, wherein the gain normalized dark current of the photodiode attributable to the dominant sources of the dark current is not multiplied by gain of the photodiode, the method comprising: applying a selected reverse bias to the photodiode to cause the photodiode to operate in the avalanche gain mode and to have a gain that reduces the gain normalized dark current of the photodiode, wherein the selected reverse bias is beyond a range in which gain and dark current both increase or decrease simultaneously.

### Claim 2 (depends on 1)

The method of claim 1, wherein the photodiode includes a photon absorption region coupled to a carrier multiplication region, wherein the dominant sources of the dark current are substantially comprised of at least one of generation-recombination current and diffusion current generated in the carrier multiplication region.

### Claim 3 (depends on 1)

The method of claim 1, wherein the photodiode has an excess noise factor that is substantially gain independent.

### Claim 4 (depends on 2)

The method of claim 2, wherein the photodiode includes an intrinsic region interposed between and coupled to the absorption region and the carrier multiplication region.

### Claim 5 (depends on 4)

The method of claim 4, wherein the absorption and carrier multiplication regions have a homojunction semiconductor architecture.

### Claim 6 (depends on 4)

The method of claim 4, wherein the absorption and carrier multiplication regions have a heterojunction semiconductor architecture.

### Claim 7 (depends on 2)

The method of claim 2, wherein the absorption region is a p+ region, and the intrinsic region is an n− region.

### Claim 8 (depends on 2)

The method of claim 2, wherein the absorption region is a n+ region, and the intrinsic region is an p− region.

### Claim 9 (depends on 1)

The method of claim 1, wherein the photodiode is a HgCdTe avalanche photodiode.

### Claim 10 (depends on 1)

The method of claim 1, wherein the selected reverse bias corresponds to a minimized gain normalized dark current for the photodiode that achieves an optimized signal-to-noise level for the photodiode.

### Claim 11 (depends on 1)

The method of claim 1, wherein the photodiode has an excess noise factor that is gain dependent.

### Claim 12 (depends on 1)

The method of claim 1, wherein the step of applying a selected reverse bias comprises:
a) applying a plurality of increasing levels of reverse bias to the photodiode, where each reverse bias level causes an increase in gain for the photodiode;
b) observing the gain normalized dark current of the photodiode for at least the last two applied reverse bias levels to determine whether the gain normalized dark current has been reduced; and
c) increasing the level of reverse bias applied to the photodiode to obtain the selected reversed bias in response to determining that the gain normalized dark current has been reduced.

### Claim 13 (depends on 12)

The method of claim 12, further comprising repeating the observing step and the increasing step until the observed gain normalized dark current is no longer being reduced.

### Claim 14 (depends on 13)

The method of claim 13, wherein the selected reverse bias applied to the photodiode is greater than 8 volts.

### Claim 15 (depends on 1)

The method of claim 1, wherein the selected reverse bias applied to the photodiode is equal to or greater than 8 volts such that photodiode has a gain greater than 100 times an input voltage corresponding to a charge absorbed by the photodiode, while the gain normalized dark current is reduced to less than 100 nA/cm2 or less.

### Claim 16 (depends on 1)

The method of claim 1, wherein the selected reverse bias applied to the photodiode is equal to or greater than 10 volts such that photodiode has a gain greater than 100 times an input voltage corresponding to a charge absorbed by the photodiode, while the gain normalized dark current is reduced to 3.4 nA/cm2 or less.