# US 10,483,417 B2 · Capacitive infrared photodetector comprising a quantum dot layer

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- Number: US 10,483,417 B2
- Document ID: US10483417B2
- Status: Granted
- Kind: B2
- Application number: 15/903,259
- Filed: 2018-02-23
- Published: 2018-08-30
- Granted: 2019-11-19
- Earliest claimed: 2017-02-24
- Assignees: The Government of the United States of America, as represented by the Secretary of the Navy
- Applicants: The Government of the United States of America, as represented by the Secretary of the Navy
- Inventors: Michael K. Yakes; María González; Phillip Jenkins; Robert J. Walters; Antonio Marti Vega; Elisa Antolín Fernández; Esther López Estrada
- Web page: https://patentgrep.com/patent/US10483417B2

## CPC

- H10F 77/1433: {Quantum dots}
- G01J 1/00: Photometry, e.g. photographic exposure meter (spectrophotometry G01J3/00; specially adapted for radiation pyrometry G01J5/00 {; exposure meters built in cameras G03B17/06})
- G01J 5/34: using capacitors, e.g. pyroelectric capacitors
- H10F 30/21: the devices being sensitive to infrared, visible or ultraviolet radiation
- H10F 30/221: the potential barrier being a PN homojunction
- H10F 30/223: the potential barrier being a PIN barrier
- H10F 30/227: the potential barrier being a Schottky barrier
- H10F 39/1847: {Multispectral infrared image sensors having a stacked structure, e.g. NPN, NPNPN or multiple quantum well [MQW] structures}
- H10F 77/1625: {Semiconductor nanoparticles embedded in semiconductor matrix}
- Y02E 10/50: Photovoltaic [PV] energy
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

A semiconductor device that utilizes intraband photon absorption in quantum dots to provide a capacitive photodetector. The presence of the quantum dots creates confined energy states within the photodetector device. Electrons are trapped in these confined energy states. When the photodetector is illuminated by light having an appropriate photon energy, the stored electrons are released to the conduction band, causing a change in the capacitance of the photodetector. By measuring this change in capacitance, light incident on the photodetector can be detected and quantified.

## Claims

### Claim 1

A photodetector device comprising:
an n-type quantum dot layer in a semiconductor heterostructure, the quantum dot layer comprising a plurality of quantum dots embedded within an n-type semiconductor host, an energy gap between valence and conduction bands of the quantum dot layer being smaller than an energy gap between valence and conduction bands of the semiconductor host;
the n-type semiconductor host being n-doped to a doping density approximately equal to a density of the quantum dots embedded in the host such that a fundamental energy level of the semiconductor host is filled with electrons;
wherein electrons within the quantum dot layer are excited upon an application of a negative electrical bias to the device and are trapped within confined states in the quantum dots, the device having a first capacitance ε/W′ at a time t1 as a result of the presence of the trapped electrons, where ε is an average dielectric permittivity of materials used in the photodetector and W′ is a space charge region of the device after the application of the electrical bias; and
wherein upon an illumination of the device by light having a photon energy at least equal to a difference between an energy of the confined electrons and a conduction band energy in the quantum dot layer, a plurality of the trapped electrons are excited into a conduction band of the quantum dot layer, the device having a second capacitance ε/W″ at a time t2 as a result of the excitement of the trapped electrons, where W″ is a space charge region of the device after excitation of the plurality of the trapped electrons into the conduction band;
wherein a difference between ε/W″ and ε/W′ is indicative of an incidence of the light on the device.

### Claim 2 (depends on 1)

The photodetector device according to claim 1,
wherein the quantum dot layer comprises a plurality of InAs quantum dots embedded within a GaAs n-type semiconductor host.

### Claim 3 (depends on 1)

The photodetector device according to claim 1, further comprising
a semi-insulating substrate;
an n+ layer grown on an upper surface of the substrate, the quantum dot layer being grown on an upper surface of the n+ layer;
an n-type layer grown on an upper surface of the n-type quantum dot layer; and
a p+ layer grown on an upper surface of the n-type layer, the n-type layer and the p+ layer forming a p-n junction, a thickness of the n-type layer being less than a thickness of a depletion region at the p-n junction.

### Claim 4 (depends on 1)

The photodetector device according to claim 1, further comprising:
a substrate;
a p+ layer grown on top of the substrate;
an n-type layer grown on top of the p+ layer, the quantum dot layer being grown on an upper surface of the n-type layer; and
an n+-type semiconductor layer (“n+-layer”) grown on top of the quantum dot layer, a thickness of the n-type layer being less than a thickness of a depletion region at a p-n junction.

### Claim 5 (depends on 1)

The photodetector device according to claim 1, further comprising:
an n+ substrate, the quantum dot layer being grown on an upper surface of the n+ substrate;
an n-type layer grown on an upper surface of the n-type quantum dot layer; and
a p+ layer grown on an upper surface of the n-type layer, the n-type layer and the p+ layer forming a p-n junction, a thickness of the n-type layer being less than a thickness of a depletion region at the p-n junction.

### Claim 6 (depends on 5)

The photodetector device according to claim 5, further comprising:
a first electrical contact connected to the p+ layer and a second electrical contact connected to the n+ substrate, the first electrical contact being in the form of a metal grid deposited on the p+ layer.

### Claim 7 (depends on 5)

The photodetector device according to claim 5, further comprising an n+ layer disposed between the n-type layer and the n+ substrate.

### Claim 8 (depends on 1)

The photodetector device according to claim 1, further comprising
a semi-insulating substrate;
an n+ layer grown on an upper surface of the substrate, the quantum dot layer being grown on an upper surface of the n+ layer;
an n-type layer grown on an upper surface of the n-type quantum dot layer; and
a metal layer grown on an upper surface of the n-type layer, the n-type layer and the metal layer forming Schottky contact, a thickness of the n-type layer being less than a thickness of a depletion region at a metal-n junction.

### Claim 9 (depends on 1)

The photodetector device according to claim 1, further comprising
a semi-insulating substrate;
an n+ layer grown on an upper surface of the substrate, the quantum dot layer being grown on an upper surface of the n+ layer;
an n-type layer grown on an upper surface of the n-type quantum dot layer;
an insulating layer grown on top of the n-type layer and
a metal layer grown on an upper surface of the insulating layer, the metal layer, the insulator layer and the n-type layer forming a metal-insulator-semiconductor structure, a thickness of the n-type layer being less than a thickness that would extend a depletion region to the quantum dot layer.

### Claim 10

A method for detecting an incidence of light on a semiconductor structure, comprising:
providing a photodetecting device, the photodetecting device comprising a semiconductor heterostructure having a quantum dot layer disposed between semiconductor layers, the quantum dot layer comprising a plurality of quantum dots embedded within an n-type semiconductor host, an energy gap between valence and conduction bands of the quantum dot layer being smaller than an energy gap between valence and conduction bands of the semiconductor host;
applying a negative bias voltage pulse to the heterostructure, the voltage pulse exciting electrons in the device and trapping the excited electrons into confined states within the quantum dots;
at time t1 after application of the voltage pulse, measuring a first capacitance ε/W′ of the device, where, ε is an average dielectric permittivity of materials used in the photodetecting device and W′ is a space charge region of the device after the application of the voltage pulse; and
at time t2>t1, measuring a second capacitance ε/W″ of the device, W″ being a space charge region of the device resulting from excitation of a plurality of the trapped electrons into a conduction band of the device;
wherein a difference between ε/W″ and ε/W′ is indicative of an incidence of light having a photon energy at least equal to a difference between an energy of the confined electrons and a conduction band energy in the quantum dot layer.

### Claim 11 (depends on 10)

The method according to claim 10, further comprising cooling the photodetecting device to inhibit an excitation of the trapped electrons through an absorption of thermal energy.

### Claim 12 (depends on 10)

The method according to claim 10, wherein a degree of difference between ε/W″ and ε/W′ is indicative of an intensity of the light incident on the device.