A photodiode is a light-sensitive semiconductor
diode
A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.
A diode ...
.
It produces current when it absorbs photons.
The package of a photodiode allows light (or infrared or ultraviolet radiation, or X-rays) to reach the sensitive part of the device. The package may include lenses or
optical filter
An optical filter is a device that selectively transmits light of different wavelengths, usually implemented as a glass plane or plastic device in the optical path, which are either dyed in the bulk or have interference coatings. The optical p ...
s. Devices designed for use specially as a photodiode use a
PIN junction rather than a
p–n junction
A p–n junction is a boundary or interface between two types of semiconductor materials, p-type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an excess of holes, while the "n" (negative) side contains ...
, to increase the speed of response. Photodiodes usually have a slower response time as their surface area increases. A photodiode is designed to operate in
reverse bias
Reverse or reversing may refer to:
Arts and media
* ''Reverse'' (Eldritch album), 2001
* ''Reverse'' (2009 film), a Polish comedy-drama film
* ''Reverse'' (2019 film), an Iranian crime-drama film
* ''Reverse'' (Morandi album), 2005
* ''Reverse'' ...
. A
solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. used to generate electric
solar power
Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovoltaic e ...
is a large area photodiode.
Photodiodes are used in scientific and industrial instruments to measure light intensity, either for its own sake or as a measure of some other property (density of smoke, for example). A photodiode can be used as the receiver of data encoded on an infrared beam, as in household
remote control
In electronics, a remote control (also known as a remote or clicker) is an electronic device used to operate another device from a distance, usually wirelessly. In consumer electronics, a remote control can be used to operate devices such as ...
s. Photodiodes can be used to form an optocoupler, allowing transmission of signals between circuits without a direct metallic connection between them, allowing isolation from high voltage differences.
Principle of operation
A photodiode is a
PIN structure or
p–n junction
A p–n junction is a boundary or interface between two types of semiconductor materials, p-type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an excess of holes, while the "n" (negative) side contains ...
. When a
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...
of sufficient energy strikes the diode, it creates an
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
–
hole
A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of en ...
pair. This mechanism is also known as the inner
photoelectric effect
The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, and solid st ...
. If the absorption occurs in the junction's
depletion region
In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region, space charge region or space charge layer, is an insulating region within a conductive, doped semiconductor material where the mobile ...
, or one diffusion length away from it, these carriers are swept from the junction by the built-in electric field of the depletion region. Thus holes move toward the
anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
, and electrons toward the
cathode
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...
, and a
photocurrent
Photocurrent is the electric current through a photosensitive device, such as a photodiode, as the result of exposure to radiant power. The photocurrent may occur as a result of the photoelectric, photoemissive, or photovoltaic effect. The photo ...
is produced. The total current through the photodiode is the sum of the dark current (current that is generated in the absence of light) and the photocurrent, so the dark current must be minimized to maximize the sensitivity of the device.
To first order, for a given spectral distribution, the photocurrent is linearly proportional to the
irradiance In radiometry, irradiance is the radiant flux ''received'' by a ''surface'' per unit area. The SI unit of irradiance is the watt per square metre (W⋅m−2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) is often used ...
.
Photovoltaic mode
![Photodiode operation](https://upload.wikimedia.org/wikipedia/commons/0/06/Photodiode_operation.png)
In photovoltaic mode (zero
bias
Bias is a disproportionate weight ''in favor of'' or ''against'' an idea or thing, usually in a way that is closed-minded, prejudicial, or unfair. Biases can be innate or learned. People may develop biases for or against an individual, a group, ...
), photocurrent flows into the anode through a short circuit to the cathode. If the circuit is opened or has a load impedance, restricting the photocurrent out of the device, a voltage builds up in the direction that forward biases the diode, that is, anode positive with respect to cathode. If the circuit is shorted or the impedance is low, a forward current will consume all or some of the photocurrent. This mode exploits the
photovoltaic effect
The photovoltaic effect is the generation of voltage and electric current in a material upon exposure to light. It is a physical property, physical and chemical phenomenon.
The photovoltaic effect is closely related to the photoelectric effect. F ...
, which is the basis for
solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. s – a traditional solar cell is just a large area photodiode. For optimum power output, the photovoltaic cell will be operated at a voltage that causes only a small forward current compared to the photocurrent.
[
]
Photoconductive mode
In photoconductive mode the diode is reverse biased, that is, with the cathode driven positive with respect to the anode. This reduces the response time because the additional reverse bias increases the width of the depletion layer, which decreases the junction's capacitance
Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...
and increases the region with an electric field that will cause electrons to be quickly collected. The reverse bias also creates dark current without much change in the photocurrent.
Although this mode is faster, the photoconductive mode can exhibit more electronic noise due to dark current or avalanche effects. The leakage current of a good PIN diode is so low (<1 nA) that the Johnson–Nyquist noise
Johnson–Nyquist noise (thermal noise, Johnson noise, or Nyquist noise) is the electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor at equilibrium, which happens rega ...
of the load resistance in a typical circuit often dominates.
Related devices
Avalanche photodiode
An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. From a functional standpoint, they can be regarded as the semiconductor analog of phot ...
s are photodiodes with structure optimized for operating with high reverse bias, approaching the reverse breakdown voltage. This allows each ''photo-generated'' carrier to be multiplied by avalanche breakdown
Avalanche breakdown (or avalanche effect) is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good ...
, resulting in internal gain within the photodiode, which increases the effective ''responsivity'' of the device.
A phototransistor is a light-sensitive transistor. A common type of phototransistor, the ''bipolar phototransistor'', is in essence a bipolar transistor
A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar t ...
encased in a transparent case so that light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...
can reach the ''base–collector junction
Junction may refer to:
Arts and entertainment
* ''Junction'' (film), a 2012 American film
* Jjunction, a 2002 Indian film
* Junction (album), a 1976 album by Andrew Cyrille
* Junction (EP), by Basement Jaxx, 2002
* Junction (manga), or ''Hot ...
''. It was invented by Dr. John N. Shive
John Northrup Shive (February 22, 1913 – June 1, 1984) was an American physicist and inventor. He made notable contributions in electronic engineering and solid-state physics during the early days of transistor development at Bell Labo ...
(more famous for his wave machine) at Bell Labs in 1948 but it was not announced until 1950. The electrons that are generated by photons in the base–collector junction are injected into the base, and this photodiode current is amplified by the transistor's current gain β (or hfe). If the base and collector leads are used and the emitter is left unconnected, the phototransistor becomes a photodiode. While phototransistors have a higher responsivity Responsivity measures the input–output Gain (electronics), gain of a detector system. In the specific case of a photodetector, it measures the electrical output per optical input.
A photodetector's responsivity is usually expressed in units of ...
for light they are not able to detect low levels of light any better than photodiodes. Phototransistors also have significantly longer response times. Another type of phototransistor, the ''field-effect phototransistor'' (also known as photoFET), is a light-sensitive field-effect transistor. Unlike photobipolar transistors, photoFETs control drain-source current by creating a gate voltage.
A solaristor
A solaristor (from SOLAR cell transISTOR) is a compact two-terminal self-powered phototransistor. The two-in-one transistor plus solar cell achieves the high-low current modulation by a memresistive effect in the flow of photogenerated carriers ...
is a two-terminal gate-less phototransistor. A compact class of two-terminal phototransistors or solaristors have been demonstrated in 2018 by ICN2 researchers. The novel concept is a two-in-one power source plus transistor device that runs on solar energy by exploiting a memresistive effect in the flow of photogenerated carriers.
Materials
The material used to make a photodiode is critical to defining its properties, because only photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...
s with sufficient energy to excite electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
s across the material's bandgap
In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in ...
will produce significant photocurrents.
Materials commonly used to produce photodiodes are listed in the table below.
Because of their greater bandgap, silicon-based photodiodes generate less noise than germanium-based photodiodes.
Binary materials, such as MoS2, and graphene emerged as new materials for the production of photodiodes.
Unwanted and wanted photodiode effects
Any p–n junction, if illuminated, is potentially a photodiode. Semiconductor devices such as diodes, transistors and ICs contain p–n junctions, and will not function correctly if they are illuminated by unwanted electromagnetic radiation (light) of wavelength suitable to produce a photocurrent. This is avoided by encapsulating devices in opaque housings. If these housings are not completely opaque to high-energy radiation (ultraviolet, X-rays, gamma rays), diodes, transistors and ICs can malfunction due to induced photo-currents. Background radiation from the packaging is also significant. Radiation hardening
Radiation hardening is the process of making electronic components and circuits resistant to damage or malfunction caused by high levels of ionizing radiation (particle radiation and high-energy electromagnetic radiation), especially for environ ...
mitigates these effects.
In some cases, the effect is actually wanted, for example to use LED
A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
s as light-sensitive devices (see LED as light sensor
In electronics, an LED circuit or LED driver is an electrical circuit used to power a light-emitting diode (LED). The circuit must provide sufficient current to light the LED at the required brightness, but must limit the current to prevent damag ...
) or even for energy harvesting
Energy harvesting (EH, also known as power harvesting or energy scavenging or ambient power) is the process by which energy is derived from external sources (e.g., solar power, thermal energy, wind energy, salinity gradients, and kinetic energ ...
, then sometimes called ''light-emitting and light-absorbing diodes'' (LEADs).
Features
Critical performance parameters of a photodiode include spectral responsivity, dark current, response time and noise-equivalent power.
; Spectral responsivity: The spectral responsivity is a ratio of the generated photocurrent to incident light power, expressed in A/ W when used in photoconductive mode. The wavelength-dependence may also be expressed as a ''quantum efficiency
The term quantum efficiency (QE) may apply to incident photon to converted electron (IPCE) ratio of a photosensitive device, or it may refer to the TMR effect of a Magnetic Tunnel Junction.
This article deals with the term as a measurement of ...
'' or the ratio of the number of photogenerated carriers to incident photons which is a unitless quantity.
; Dark current: The dark current is the current through the photodiode in the absence of light, when it is operated in photoconductive mode. The dark current includes photocurrent generated by background radiation and the saturation current of the semiconductor junction. Dark current must be accounted for by calibration
In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of know ...
if a photodiode is used to make an accurate optical power measurement, and it is also a source of noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...
when a photodiode is used in an optical communication system.
; Response time
Response time may refer to:
*The time lag between an electronic input and the output signal which depends upon the value of passive components used.
* Responsiveness, how quickly an interactive system responds to user input
* Response time (biolog ...
: The response time is the time required for the detector to respond to an optical input. A photon absorbed by the semiconducting material will generate an electron–hole pair which will in turn start moving in the material under the effect of the electric field and thus generate a current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
. The finite duration of this current is known as the transit-time spread and can be evaluated by using Ramo's theorem. One can also show with this theorem that the total charge generated in the external circuit is e and not 2e as one might expect by the presence of the two carriers. Indeed, the integral
In mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented i ...
of the current due to both electron and hole over time must be equal to e. The resistance and capacitance of the photodiode and the external circuitry give rise to another response time known as RC time constant
The RC time constant, also called tau, the time constant (in seconds) of an RC circuit, is equal to the product of the circuit resistance (in ohms) and the circuit capacitance (in farads), i.e.
: \tau = RC econds
It is the time required to c ...
(). This combination of R and C integrates the photoresponse over time and thus lengthens the impulse response
In signal processing and control theory, the impulse response, or impulse response function (IRF), of a dynamic system is its output when presented with a brief input signal, called an Dirac delta function, impulse (). More generally, an impulse ...
of the photodiode. When used in an optical communication system, the response time determines the bandwidth available for signal modulation and thus data transmission.
; Noise-equivalent power Noise-equivalent power (NEP) is a measure of the sensitivity of a photodetector or detector system. It is defined as the signal power that gives a signal-to-noise ratio of one in a one hertz output bandwidth. An output bandwidth of one hertz is equi ...
: Noise-equivalent power (NEP) is the minimum input optical power to generate photocurrent, equal to the rms noise current in a 1 hertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...
bandwidth. NEP is essentially the minimum detectable power. The related ''characteristic detectivity'' () is the inverse of NEP (1/NEP) and the ''specific detectivity
Specific detectivity, or ''D*'', for a photodetector is a figure of merit used to characterize performance, equal to the reciprocal of noise-equivalent power (NEP), normalized per square root of the sensor's area and frequency bandwidth (reciproca ...
'' () is the detectivity multiplied by the square root of the area () of the photodetector () for a 1 Hz bandwidth. The specific detectivity allows different systems to be compared independent of sensor area and system bandwidth; a higher detectivity value indicates a low-noise device or system. Although it is traditional to give () in many catalogues as a measure of the diode's quality, in practice, it is hardly ever the key parameter.
When a photodiode is used in an optical communication system, all these parameters contribute to the '' sensitivity'' of the optical receiver which is the minimum input power required for the receiver to achieve a specified ''bit error rate
In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors.
The bit error rate (BER) i ...
''.
Applications
P–n photodiodes are used in similar applications to other photodetector
Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as Photoelectric effect, photoelectric or photoc ...
s, such as photoconductor
Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation.
W ...
s, charge-coupled device
A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...
s (CCD), and photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal.
Kinds of photomultiplier include:
* Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for sho ...
tubes. They may be used to generate an output which is dependent upon the illumination (analog for measurement), or to change the state of circuitry (digital, either for control and switching or for digital signal processing).
Photodiodes are used in consumer electronics
Consumer electronics or home electronics are electronic (analog or digital) equipment intended for everyday use, typically in private homes. Consumer electronics include devices used for entertainment, communications and recreation. Usually r ...
devices such as compact disc
The compact disc (CD) is a Digital media, digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then rele ...
players, smoke detector
A smoke detector is a device that senses smoke, typically as an indicator of fire. Smoke detectors are usually housed in plastic enclosures, typically shaped like a disk about in diameter and thick, but shape and size vary. Smoke can be detecte ...
s, medical devices[E. Aguilar Pelaez et al., "LED power reduction trade-offs for ambulatory pulse oximetry," 2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Lyon, 2007, pp. 2296-2299. doi: 10.1109/IEMBS.2007.4352784, URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4352784&isnumber=4352185] and the receivers for infrared remote control devices used to control equipment from televisions
Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, e ...
to air conditioners. For many applications either photodiodes or photoconductors may be used. Either type of photosensor may be used for light measurement, as in camera
A camera is an Optics, optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), ...
light meters, or to respond to light levels, as in switching on street lighting after dark.
Photosensors of all types may be used to respond to incident light or to a source of light which is part of the same circuit or system. A photodiode is often combined into a single component with an emitter of light, usually a light-emitting diode
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (cor ...
(LED), either to detect the presence of a mechanical obstruction to the beam (slotted optical switch
The slotted optical switch, sometimes known as opto switch or optical switch but not to be confused with the optical component, is a device comprising a photoemitter (e.g. LED) and a photodetector (e.g. photodiode) mounted in a single package ...
) or to couple
Couple or couples may refer to :
Basic meaning
*Couple (app), a mobile app which provides a mobile messaging service for two people
*Couple (mechanics), a system of forces with a resultant moment but no resultant force
*Couple (relationship), tw ...
two digital or analog circuits while maintaining extremely high electrical isolation
Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no direct conduction path is permitted.John Huntington ''Show Networks and Control Systems: Formerly Control Systems for Live E ...
between them, often for safety (optocoupler
An opto-isolator (also called an optocoupler, photocoupler, or optical isolator) is an electronic component that transfers electrical signals between two isolated circuits by using light. Opto-isolators prevent high voltages from affecting the ...
). The combination of LED and photodiode is also used in many sensor
A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon.
In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...
systems to characterize different types of products based on their optical absorbance.
Photodiodes are often used for accurate measurement of light intensity in science and industry. They generally have a more linear response than photoconductors.
They are also widely used in various medical applications, such as detectors for computed tomography (coupled with scintillator
A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate (i.e. re-emit the absorbed ...
s), instruments to analyze samples (immunoassay
An immunoassay (IA) is a biochemical test that measures the presence or concentration of a macromolecule or a small molecule in a solution through the use of an antibody (usually) or an antigen (sometimes). The molecule detected by the immunoass ...
), and pulse oximeter
Pulse oximetry is a noninvasive method for monitoring a person's oxygen saturation. Peripheral oxygen saturation (SpO2) readings are typically within 2% accuracy (within 4% accuracy in 95% of cases) of the more accurate (and invasive) reading o ...
s.
PIN diode
A pin is a device used for fastening objects or material together.
Pin or PIN may also refer to:
Computers and technology
* Personal identification number (PIN), to access a secured system
** PIN pad, a PIN entry device
* PIN, a former Dutch de ...
s are much faster and more sensitive than p–n junction diodes, and hence are often used for optical communications and in lighting regulation.
P–n photodiodes are not used to measure extremely low light intensities. Instead, if high sensitivity is needed, avalanche photodiode
An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. From a functional standpoint, they can be regarded as the semiconductor analog of phot ...
s, intensified charge-coupled device
A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...
s or photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal.
Kinds of photomultiplier include:
* Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for sho ...
tubes are used for applications such as astronomy
Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
, spectroscopy
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
, night vision equipment
A night-vision device (NVD), also known as a night optical/observation device (NOD), night-vision goggle (NVG), is an optoelectronic device that allows visualization of images in low levels of light, improving the user's night vision. The dev ...
and laser rangefinding.
Comparison with photomultipliers
Advantages compared to photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal.
Kinds of photomultiplier include:
* Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for sho ...
s:
# Excellent linearity of output current as a function of incident light
# Spectral response from 190 nm to 1100 nm (silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
), longer wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
s with other semiconductor materials
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...
# Low noise
# Ruggedized to mechanical stress
# Low cost
# Compact and light weight
# Long lifetime
# High quantum efficiency
The term quantum efficiency (QE) may apply to incident photon to converted electron (IPCE) ratio of a photosensitive device, or it may refer to the TMR effect of a Magnetic Tunnel Junction.
This article deals with the term as a measurement of ...
, typically 60–80%
# No high voltage required
Disadvantages compared to photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal.
Kinds of photomultiplier include:
* Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for sho ...
s:
# Small area
# No internal gain (except avalanche photodiode
An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. From a functional standpoint, they can be regarded as the semiconductor analog of phot ...
s, but their gain is typically 102–103 compared to 105-108 for the photomultiplier)
# Much lower overall sensitivity
# Photon counting only possible with specially designed, usually cooled photodiodes, with special electronic circuits
# Response time for many designs is slower
# Latent effect
Pinned photodiode
The pinned photodiode (PPD) has a shallow implant (P+ or N+) in N-type or P-type diffusion layer, respectively, over a P-type or N-type (respectively) substrate layer, such that the intermediate diffusion layer can be fully depleted of majority carriers, like the base region of a bipolar junction transistor
A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar ...
. The PPD (usually PNP) is used in CMOS
Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFE ...
active-pixel sensor
An active-pixel sensor (APS) is an image sensor where each pixel sensor unit cell has a photodetector (typically a pinned photodiode) and one or more active transistors. In a metal–oxide–semiconductor (MOS) active-pixel sensor, MOS field-effec ...
s; a precursor NPN variant with a clocked top N layer was invented at Sony in 1975 for use in CCD image sensors.
Early charge-coupled device image sensor
An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of curr ...
s suffered from shutter lag In photography, shutter lag is the delay between triggering the shutter and when the photograph is actually recorded. This is a common problem in the photography of fast-moving objects or animals and people in motion. The term narrowly refers only t ...
. This was largely resolved with the invention of the pinned photodiode. It was invented by Nobukazu Teranishi
is a Japanese engineer who researches image sensors, and is known for inventing the pinned photodiode, an important component of modern digital cameras. He was one of four recipients of the 2017 Queen Elizabeth Prize for Engineering. His industr ...
, Hiromitsu Shiraki and Yasuo Ishihara at NEC
is a Japanese multinational information technology and electronics corporation, headquartered in Minato, Tokyo. The company was known as the Nippon Electric Company, Limited, before rebranding in 1983 as NEC. It provides IT and network soluti ...
in 1980. They recognized that lag can be eliminated if the signal carriers could be transferred from the photodiode to the CCD. This led to their invention of the pinned photodiode, a photodetector structure with low lag, low noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...
, high quantum efficiency
The term quantum efficiency (QE) may apply to incident photon to converted electron (IPCE) ratio of a photosensitive device, or it may refer to the TMR effect of a Magnetic Tunnel Junction.
This article deals with the term as a measurement of ...
and low dark current. It was first publicly reported by Teranishi and Ishihara with A. Kohono, E. Oda and K. Arai in 1982, with the addition of an anti-blooming structure. The new photodetector structure invented at NEC was given the name "pinned photodiode" (PPD) by B.C. Burkey at Kodak in 1984. In 1987, the PPD began to be incorporated into most CCD sensors, becoming a fixture in consumer electronic video cameras
A video camera is an optical instrument that captures videos (as opposed to a movie camera, which records images on film). Video cameras were initially developed for the television industry but have since become widely used for a variety of other ...
and then digital still camera
A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devices ...
s.
In 1994, Eric Fossum
Eric R. Fossum (born October 17, 1957) is an American physicist and engineer, which with the help of other JPL scientists, co-developed some features of the CMOS sensor, CMOS image sensor. He is currently a professor at Thayer School of Engineerin ...
, while working at NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
's Jet Propulsion Laboratory
The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States.
Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...
(JPL), proposed an improvement to the CMOS sensor
An active-pixel sensor (APS) is an image sensor where each pixel sensor unit cell has a photodetector (typically a pinned photodiode) and one or more active transistors. In a metal–oxide–semiconductor (MOS) active-pixel sensor, MOS field-effec ...
: the integration of the pinned photodiode. A CMOS sensor with PPD technology was first fabricated in 1995 by a joint JPL and Kodak
The Eastman Kodak Company (referred to simply as Kodak ) is an American public company that produces various products related to its historic basis in analogue photography. The company is headquartered in Rochester, New York, and is incorpor ...
team that included Fossum along with P.P.K. Lee, R.C. Gee, R.M. Guidash and T.H. Lee. Since then, the PPD has been used in nearly all CMOS sensors. The CMOS sensor with PPD technology was further advanced and refined by R.M. Guidash in 1997, K. Yonemoto and H. Sumi in 2000, and I. Inoue in 2003. This led to CMOS sensors achieve imaging performance on par with CCD sensors, and later exceeding CCD sensors.
Photodiode array
A one-dimensional array of hundreds or thousands of photodiodes can be used as a position sensor
A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon.
In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...
, for example as part of an angle sensor.[
] A two-dimensional array is used in image sensors and optical mice.
In some applications, photodiode arrays allow for high-speed parallel readout, as opposed to integrating scanning electronics as in a charge-coupled device
A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...
(CCD) or CMOS sensor
An active-pixel sensor (APS) is an image sensor where each pixel sensor unit cell has a photodetector (typically a pinned photodiode) and one or more active transistors. In a metal–oxide–semiconductor (MOS) active-pixel sensor, MOS field-effec ...
. The optical mouse chip shown in the photo has parallel (not multiplexed) access to all 16 photodiodes in its 4 × 4 array.
Passive-pixel image sensor
The passive-pixel sensor
An active-pixel sensor (APS) is an image sensor where each pixel sensor unit cell has a photodetector (typically a pinned photodiode) and one or more active transistors. In a metal–oxide–semiconductor (MOS) active-pixel sensor, MOS field-effec ...
(PPS) is a type of photodiode array. It was the precursor to the active-pixel sensor
An active-pixel sensor (APS) is an image sensor where each pixel sensor unit cell has a photodetector (typically a pinned photodiode) and one or more active transistors. In a metal–oxide–semiconductor (MOS) active-pixel sensor, MOS field-effec ...
(APS). A passive-pixel sensor consists of passive pixels which are read out without amplification, with each pixel consisting of a photodiode and a MOSFET
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
switch. In a photodiode array, pixels contain a p–n junction
A p–n junction is a boundary or interface between two types of semiconductor materials, p-type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an excess of holes, while the "n" (negative) side contains ...
, integrated capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
, and MOSFETs as selection transistors
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
. A photodiode array was proposed by G. Weckler in 1968, predating the CCD. This was the basis for the PPS.
The noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...
of photodiode arrays is sometimes a limitation to performance. It was not possible to fabricate active pixel sensors with a practical pixel size in the 1970s, due to limited microlithography
Microlithography is a general name for any manufacturing process that can create a minutely patterned thin film of protective materials over a substrate, such as a silicon wafer, in order to protect selected areas of it during subsequent etching ...
technology at the time.[
]
See also
* Electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
* Band gap
In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in ...
* Infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
* Optoelectronics
Optoelectronics (or optronics) is the study and application of electronic devices and systems that find, detect and control light, usually considered a sub-field of photonics. In this context, ''light'' often includes invisible forms of radiatio ...
* Optical interconnect
In integrated circuits, optical interconnects refers to any system of transmitting signals from one part of an integrated circuit to another using light. Optical interconnects have been the topic of study due to the high latency and power consumpt ...
* Light Peak
Thunderbolt is the brand name of a hardware interface for the connection of external peripherals to a computer. It has been developed by Intel, in collaboration with Apple. It was initially marketed under the name Light Peak, and first sold ...
* Interconnect bottleneck
The interconnect bottleneck comprises limits on integrated circuit (IC) performance due to connections between components instead of their internal speed.
In 2006 it was predicted to be a "looming crisis" by 2010.
Improved performance of compute ...
* Optical fiber cable
A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable, but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with ...
* Optical communication
* Parallel optical interface
* Opto-isolator
An opto-isolator (also called an optocoupler, photocoupler, or optical isolator) is an electronic component that transfers electrical Signal, signals between two isolated circuits by using light. Opto-isolators prevent high voltages from affecti ...
* Semiconductor device
A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. Its conductivity li ...
* Solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.
* Avalanche photodiode
An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. From a functional standpoint, they can be regarded as the semiconductor analog of phot ...
* Transducer
A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another.
Transducers are often employed at the boundaries of automation, measurement, and contr ...
* LEDs as photodiode light sensors
In electronics, an LED circuit or LED driver is an electrical Electric circuit, circuit used to power a light-emitting diode (LED). The circuit must provide sufficient current to light the LED at the required brightness, but must limit the current ...
* Light meter
A light meter is a device used to measure the amount of light. In photography, a light meter (more correctly an exposure meter) is used to determine the proper exposure for a photograph. The meter will include either a digital or analog calcul ...
* Image sensor
An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of curr ...
* Transimpedance amplifier
In electronics, a transimpedance amplifier (TIA) is a current to voltage converter, almost exclusively implemented with one or more operational amplifiers. The TIA can be used to amplify the current output of Geiger–Müller tubes, photo multipli ...
References
External links
Photodiode I–V characteristics
Using the Photodiode to convert the PC to a Light Intensity Logger
Design Fundamentals for Phototransistor Circuits
(archived on February 5, 2005)
Excelitas Application Notes on Pacer Website
(archived on March 4, 2016)
{{Authority control
Optical diodes
Photodetectors
Silicon photonics devices