Photodiodes: detailed in simple language. Main characteristics and parameters of photodiodes Photodiode as a power source

Purpose: photodiode- a receiver of optical radiation, which converts the light that has fallen on its photosensitive area into an electric charge.

Operating principle: The simplest photodiode is a conventional semiconductor diode, which provides the possibility of exposure to optical radiation on the p–n junction. When exposed to radiation in a direction perpendicular to the plane of the p-n junction, as a result of the absorption of photons with an energy greater than the band gap, electron-hole pairs appear in the n-region. These electrons and holes are called photocarriers. When photocarriers diffuse deep into the n region, the main fraction of electrons and holes does not have time to recombine and reaches the p–n junction boundary. Here, the photocarriers are separated by the electric field of the p–n junction, and the holes pass into the p region, while the electrons cannot overcome the transition field and accumulate at the interface between the p–n junction and the n region. Thus, the current through the p–n junction is due to the drift of minority carriers – holes. The drift current of photocarriers is called photocurrent.

Photodiodes can operate in one of two modes - without an external source of electrical energy (photogenerator mode) or with an external source of electrical energy (photoconverter mode).

Device: structural diagram of a photodiode. 1 - semiconductor crystal; 2 - contacts; 3 - conclusions; Ф - flux of electromagnetic radiation; E - direct current source; Rн - load.

Options: sensitivity (reflects the change in the electrical state at the output of the photodiode when a single optical signal is applied to the input.); noise (in addition to the useful signal, a chaotic signal appears at the output of the photodiode with a random amplitude and spectrum- photodiode noise)

Characteristics: a) current-voltage characteristic photodiode is the dependence of the output voltage on the input current. b) light characteristic the dependence of the photocurrent on the illumination corresponds to the direct proportionality of the photocurrent on the illumination. c) spectral characteristic of the photodiode is the dependence of the photocurrent on the wavelength of the incident light on the photodiode.

Application: a) optoelectronic integrated circuits.

b) multi-element photodetectors.c) optocouplers.

9. LEDs. Purpose, device, principle of operation, basic parameters and characteristics.

Purpose: LED A semiconductor device that emits light when current is passed through it in the forward direction.

Principle of operation: The work is based on the physical phenomenon of the occurrence of light radiation during the passage of electric current through the p-n-junction. The color of the glow (the wavelength of the emission spectrum maximum) is determined by the type of semiconductor materials used that form the p-n junction.

The LED is a semiconductor emitting device with one or more n-p junctions, which converts electrical energy into the energy of incoherent light radiation. Radiation occurs as a result of the recombination of injected carriers in one of the regions adjacent to the n-p junction. Recombination occurs when carriers move from upper levels to lower ones.

Characteristics and parameters: the main parameter of LEDs is the internal quantum efficiency (the ratio of the number of photons to the number of carriers injected into the base) and external efficiency (the ratio of the photon flux from the LED to the charge carrier flux in it). External efficiency is largely determined by technology and with the growth of its level can be significantly increased.

The main characteristics of LEDs are current-voltage, brightness and spectral. The main parameters of light emitting diodes are the wavelength, half-width of the emission spectrum, emission power, operating frequency and radiation pattern.

LEDs are widely used in digital indicators, light displays, and optoelectronic devices. In principle, it is possible to form a color television screen on their basis.

A special place in electrical engineering is occupied by photodiodes, which are used in various devices and devices. A photodiode is a semiconductor element that is similar in its properties to a simple diode. Its reverse current directly depends on the intensity of the light flux falling on it. Most often, semiconductor elements with a p-n junction are used as a photodiode.

Device and principle of operation

The photodiode is part of many electronic devices. That is why it has gained wide popularity. An ordinary LED is a diode with a p-n junction, the conductivity of which depends on the light falling on it. In the dark, the photodiode has the characteristics of a conventional diode.

1 - semiconductor junction.
2 - positive pole.
3 - photosensitive layer.
4 - negative pole.

Under the action of a light flux on the transition plane, photons are absorbed with an energy exceeding the limiting value; therefore, pairs of charge carriers - photocarriers - are formed in the n-region.

When mixing photocarriers in the depth of the "n" region, the main part of the carriers does not have time to recombine and passes to the p-n boundary. At the transition, the photocarriers are separated by an electric field. In this case, the holes pass into the “p” region, and the electrons are not able to go through the transition, therefore they accumulate near the border of the p-n transition, as well as the “n” region.

The reverse current of the diode increases when exposed to light. The value by which the reverse current increases is called the photocurrent.

Photocarriers in the form of holes carry out a positive charge of the "p" region with respect to the "n" region. In turn, the electrons produce a negative charge in the "n" region relative to the "p" region. The resulting potential difference is called the photoelectromotive force, and is denoted by "E f". The electric current that occurs in the photodiode is reverse, and is directed from the cathode to the anode. Moreover, its value depends on the amount of illumination.

Operating modes

Photodiodes are capable of operating in the following modes:

• Photogenerator mode. No electricity connection.
• Photoconverter mode. With external power supply connection.

In work photogenerator photodiodes are used instead of a power source that convert sunlight into electrical energy. Such photo generators are called solar cells. They are the main parts of solar panels used in various devices, including those on spacecraft.

The efficiency of silicon-based solar cells is 20%, for film cells this parameter is much higher. An important property of solar cells is the dependence of the output power on the weight and area of ​​the sensitive layer. These properties reach values ​​of 200 W/kg and 1 kW/m 2 .

When the photodiode functions as photoconverter , the voltage source is connected to the circuit with reverse polarity. In this case, reverse graphs of the current-voltage characteristic are used for different illumination conditions.

The voltage and current at the load R n are determined on the graph by the intersections of the characteristics of the photodiode and the load line, which corresponds to the resistor R n. In the dark, the photodiode is equivalent in its action to a conventional diode. The current in the dark mode for silicon diodes ranges from 1 to 3 microamperes, for germanium diodes from 10 to 30 microamperes.

Types of photodiodes

There are several different types of photodiodes that have their own advantages.

p – i – nphotodiode

In the p-n region, this diode has a section with high resistance and intrinsic conductivity. When exposed to light, pairs of holes and electrons appear. The electric field in this zone has a constant value, there is no space charge.

This auxiliary layer significantly reduces the capacitance of the barrier layer, and is independent of voltage. This expands the operating frequency band of the diodes. As a result, the speed rises sharply, and the frequency reaches 10 10 hertz. The increased resistance of this layer significantly reduces the operating current in the absence of lighting. In order for the light flux to be able to penetrate the p-layer, it must not be thick.

Avalanche photodiodes

This type of diode is a highly sensitive semiconductor that converts light into an electric current signal using the photoelectric effect. In other words, these are photodetectors that amplify the signal due to the avalanche multiplication effect.

1 - ohmic contacts 2 - anti-reflective coating

Avalanche photodiodes are more sensitive than other photodetectors. This makes it possible to use them for low light powers.

Superlattices are used in the design of avalanche photodiodes. Their essence lies in the fact that significant differences in the impact ionization of carriers lead to a drop in noise.

Another advantage of using similar structures is the localization of avalanche breeding. It also reduces interference. In the superlattice, the thickness of the layers is from 100 to 500 angstroms.

Operating principle

At a reverse voltage close to the avalanche breakdown value, the photocurrent sharply increases due to the impact ionization of charge carriers. The action is that the energy of the electron rises from the external field and can exceed the ionization limit of the substance, as a result of which the meeting of this electron with an electron from the valence band will lead to the appearance of a new pair of electron and hole. The charge carriers of this pair will be accelerated by the field and may contribute to the formation of new charge carriers.

Characteristics

The properties of such light diodes can be described by some dependencies.

Volt-ampere

This characteristic is the dependence of the current strength at a constant flux of light on the voltage.

I- current M- multiplication factor U- voltage

Luminous

This property is the dependence of the diode current on illumination. As the light flux increases, the photocurrent increases.

Spectral

This property is the dependence of the diode current on the wavelength of the light, and is the width of the boundary zone.

Time constant

This is the time it takes for the photocurrent of the diode to change after the light is applied compared to the steady state value.

dark resistance

This is the resistance value of the diode in the dark.

inertia

Factors affecting this characteristic:

• Diffusion time of nonequilibrium charge carriers.
• Time of passage along the p-n transition.
• The period of recharging the capacitance of the p-n junction barrier.

Scope of application

Photodiodes are the main elements of many optoelectronic devices.

Integrated circuits (optoelectronic)

A photodiode can have a significant operating speed, but the current amplification factor is no more than unity. Due to the optical connection, microcircuits have significant advantages: ideal galvanic isolation of control circuits from powerful power circuits. At the same time, a functional relationship is maintained between them.

Photodetectors with multiple elements

These devices in the form of a photodiode matrix, a scanner, are new progressive electronic devices. Their optoelectronic eye with a photodiode can create a response to the spatial and brightness properties of objects. In other words, he can see his complete visual image.

The number of cells sensitive to light is very large. Therefore, in addition to issues of speed and sensitivity, it is necessary to read information. All photodetectors with multiple photocells are scanning systems, that is, devices that allow you to analyze the studied space by sequential element-by-element viewing.

Photodiodes are also widely used in fiber optic lines and laser rangefinders. Recently, such light diodes have been used in positron emission tomography.

At present, there are samples of photosensitive matrices consisting of avalanche photodiodes. Their effectiveness and scope depends on several factors.

The most influential factors were:

• The total leakage current resulting from the addition of noise and current in the absence of light.
• Quantum efficiency, which determines the proportion of incident quanta, leading to the appearance of current and charge carriers.

Lab #16

Photodiode study

Target: Familiarize yourself with the principle of operation, device, characteristics and application of semiconductor photodiodes.

Instruments and accessories: germanium photodiode FD-7G, stand for measuring the current-voltage characteristics of diodes, optical bench with an illuminator, power supply, oscilloscope.

Theoretical introduction

photodiode called a semiconductor diode that is sensitive to light and designed to convert the light flux (optical radiation) into an electrical signal.

Not differing in the principle of operation from the photoconverter of solar energy, photodiodes have their own design features and characteristics, which are determined by their purpose.

Photodiodes are intended for use as receivers and sensors of optical radiation (usually visible and infrared) as part of equipment and various devices that use visible and infrared radiation.

The operation of photodiodes is based on the phenomenon of the internal photoelectric effect, in which, under the action of light, additional (nonequilibrium) electrons and holes appear in the semiconductor, creating a photocurrent or photovoltage.

1. The principle of operation of photodiodes with a p-n junction. In photodiodes, the photosensitive element is the transition region - p-n-junction, located between the regions with electronic and hole conductivity (Fig. 1).

Formation of a p-n junction. An n-type semiconductor contains a certain amount of impurity donor-type atoms, which are almost all ionized at room temperature. Thus, in such a semiconductor there are n o free electrons and the same number of immobile positively charged ions of the donor impurity.

A similar situation occurs in a hole semiconductor (p-type semiconductor). It has p about free holes and the same number of negatively charged ions of acceptor atoms. The principle of formation of a p-n junction is shown in fig. 1.

When the p- and n-regions come into contact in them, due to the presence of a concentration gradient of electrons and holes, a diffusion flow of electrons from the n-type semiconductor to the p-type semiconductor arises and, conversely, a hole flow from the p-semiconductor to the n-semiconductor. The electrons that have passed from the n-region to the p-region recombine with holes near the interface. Holes recombine similarly, moving from the p-region to the n-region. As a result, there are practically no free charge carriers (electrons and holes) near the p-n junction.

Thus, on both sides of the p-n junction, a double charged layer formed by immobile impurity ions (other names - a depletion layer or a space charge region (SCR), a blocking layer) is formed, which creates a strong electric field. The electric field of the blocking layer is directed from the n-region to the p-region and counteracts the process of diffusion of the main charge carriers from the regions remote from the p-n junction to the depleted region. Such a state is equilibrium and, in the absence of external perturbations, can exist for an arbitrarily long time.

Rice. 1 – Formation of p-n-junction Fig. 2

How a photodiode works. Optical radiation (light) absorbed in a semiconductor structure with a p-n junction creates free electron-hole pairs, provided that the photon energy hν exceeds the band gap of the semiconductor Eg.

Free electrons and holes arise both in the p- and n-junction regions and in the immediate vicinity of the blocking layer. The electric field existing in the blocking layer (the field of the p-n junction) separates the free charge carriers created by light, depending on their sign, into different parts of the photodiode: free electrons move to the n-region of the junction, and holes move to the p-region, which leads to the charging of these areas (Fig. 2).

When illuminated, holes accumulate in the p-region, charging it positively. Electrons accumulate in the n-region, charging it negatively. Therefore, there is a potential difference between them.

In this case, two modes of operation of the device are possible: in circuits with an external power source and without it. The mode of operation of a photodiode with an external power source is called photodiode, and without an external power source, it is called the photovoltage generation mode (another name is photovoltaic mode).

Generation mode. In this case, no external voltage is applied to the junction and the circuit is open. Illumination leads to the accumulation of photoelectrons in the n-region and holes in the p-region. As a result, a potential difference U f is formed (often called "voltage

Rice. 3 Fig.4 - Volt-ampere characteristics of the photodiode

at different light fluxes (Ф 1< Ф 2 < Ф 3).

idling U xx "), that is, a photo-emf appears. The accumulation of excess electrons and holes is not unlimited. Simultaneously with an increase in the concentration of holes in the hole region and electrons in the electronic region, the potential barrier of the transition decreases by the value of the photovoltage and diffusion of the majority charge carriers through the p-n junction occurs. There is a dynamic balance.

When connected to the external terminals of the load photodiode R n, a current will appear in its circuit (Fig. 3). In the external circuit, the photocurrent is directed from the p region to the n region. Under such conditions, the photodiode works as a converter of radiation energy into electrical energy.

Volt-ampere characteristic of the illuminated p-n-junction. The current-voltage characteristic of the pn junction under illumination can be written in the following form:

, (1)

where I n - saturation current in the dark; I f - photocurrent, that is, the current created by charge carriers excited by light and passing through the pn junction; U is the external voltage at the junction.

On fig. Figure 4 shows graphs of current-voltage dependences for various light fluxes F. In the absence of illumination (I f = 0), the current-voltage (dark) characteristic passes through the origin. The remaining curves corresponding to certain light fluxes are shifted along the ordinate axis (current axis) into segments equal to the strength of the photocurrent - I f. It can be seen from expression (1) that with the reverse inclusion (U< 0) и при

(qU >> kT) current through the transition I \u003d - (I n + I f).

Parts of the curves located in the third quadrant correspond to the photodiode operation mode): parts of the curves located in the fourth quadrant correspond to the photovoltage generation mode.

If in the external circuit the current strength I \u003d 0 (the circuit is open), then from expression (1) you can find the open circuit voltage U f.

(2)

If the photodiode in the generation mode is connected to an external circuit with low resistance, then photoelectrons in the n-region do not accumulate and U f = 0. And since there is no external voltage, the current I = - I f flows in the circuit, often called short-circuit current and directly proportional to the luminous flux I f ~ F.

Rice. 5 - Structural diagram of the photodiode and circuit

turning it on when working in the photodiode mode: Fig.6

1 - semiconductor crystal; 2 - contacts;

3 - conclusions; Ф - electromagnetic flux

radiation; n and p are semiconductor regions;

E - direct current source; R n - load.

photodiode mode. In this mode, a reverse voltage is applied to the p-n junction

(the p-region is connected to the minus of the voltage source, and the n-region to the plus of the source; Fig. 5). The circuit also includes a load resistance (resistor) R n. In this case, the transition has a huge resistance and a weak reverse current flows through it (saturation current in the dark I n). When the photodiode is illuminated, the current through it increases sharply due to the appearance of a photocurrent and can significantly exceed the dark current I n (Fig. 4). Accordingly, the voltage drop across the load resistance R n also changes. With the right choice of voltage source and external resistance R n, the magnitude of the electrical signal (voltage across the resistor) can be large, and therefore photodiodes are widely used to record and measure light signals.

The current through the photodiode is mainly determined by the fluxes of minor nonequilibrium charge carriers (electrons in the p-region and holes in the n-region) that occur during illumination, and does not depend on voltage, that is, it has the character of a saturation current. Therefore, in the photodiode mode, a strict linear dependence of the photocurrent on illumination is observed up to very high illumination values. This is an important advantage of photodiodes.

To register variable optical signals (light fluxes), the scheme shown in fig. 6. The changing light flux incident on the photodiode causes an alternating current component in the circuit, which repeats the changes in light intensity. And on the resistor R n the same voltage changes occur, which is fed to the input of the recording system. In order to separate (not skip) the constant component of the voltage across the resistor, a separating capacitor C is located in the signal circuit.

2. Manufacturing technology and design. For the manufacture of pn junctions in the production of photodiodes, the impurity fusion method and diffusion are used. In this case, the main attention is paid to the depth of the p-n junction relative to

Fig.7 - Construction of geranium Fig.8 - Spectral characteristics

photodiode FD-1. germanium (1) and silicon photodiodes (2).

illuminated crystal surface, since it determines the inertia (speed) of the photodiode. Figure 7 shows the design of the germanium photodiode FD-1 in a metal case. Round plate 1, cut from a single crystal of germanium with n-type electrical conductivity, is fixed with the help of a crystal holder 2 in a kovar case 3. Conclusion 4 from an indium electrode fused into germanium is passed through a kovar tube 5 fixed by a glass insulator 6 in the leg of the case 7. Another the electrode is the photodiode case itself, since the germanium crystal is soldered to the crystal holder with a tin ring 8. The photodiode case has a round hole closed by a glass lens 9, which collects the light flux on the limited surface of the germanium plate. To protect the p-n-junction from environmental influences, the photodiode body is sealed.

Some types of photodiodes have a plastic housing. The material of such a housing and a window in a metal housing is chosen so that they are transparent for that part of the spectrum (radiation) to which this photodiode should be sensitive. So, for germanium devices, this is visible light and short-wave infrared radiation.

Materials, from which photodiodes are made, are Ge, Si, GaAs, HgCdTe and other semiconductor compounds.

Main characteristics and parameters of photodiodes

- Sensitivity S - parameter that reflects the change in the electrical signal (current or voltage) at the output of the photodiode when it is illuminated.

It is quantitatively measured by the ratio of the change in the electrical characteristic (current strength I f or voltage U f), taken at the output of the photodiode, to the radiation flux Ф incident on the device.

S I \u003d I f / F- current sensitivity, S v \u003d U f / F- voltage sensitivity.

- Sensitivity threshold F p- the value of the minimum luminous flux recorded by the photodiode, referred to the unit of the operating frequency band.

- Time constant τ, which characterizes the inertia of the device, that is, its speed.

This is the time during which the photodiode photocurrent changes after illumination or after darkening of the photodiode by e times with respect to the steady value.

For photodiodes with p-n-junction, it is 10 -6 - 10 -8 s.

- Dark resistance R T is the resistance of the photodiode in the absence of illumination.

- Spectral characteristic is the dependence of the photocurrent on the wavelength λ of the light incident on the photodiode. For germanium and silicon photodiodes, the spectral characteristics are shown in Fig. 8. The wavelength, which accounts for the maximum sensitivity, for silicon photodiodes is approximately equal to λmax = 800 - 900 nm, for germanium photodiodes it is at λmax = 1500 - 1600 nm.

- Volt-ampere characteristics- the dependence of the light current on the voltage at a constant light flux.

- Light characteristic - dependence of photocurrent on illumination.

Some other parameters are shown in the table.

The conventional graphic designation of photodiodes is shown in Fig. 9, photographs of some photodiodes are shown in Fig. 10.

Rice. 9 Fig.10

4. Application of photodiodes. Modern photodiodes have the best combination of the main parameters:

1. High sensitivity to optical signals;

2. High performance;

3. Low operating voltage;

4. Linear dependence of photocurrent on illumination in a wide range of illumination.

5. Low noise;

6. Simplicity of the device.

Therefore, they are widely used in automation devices, computer and laser technology, fiber-optic communication lines.

In everyday life, photodiodes are used in devices such as CD-ROM drives, modern cameras, and various touch devices.

For example, infrared photodiodes are used in remote controls, security, security and automation systems.

There are X-ray photodiodes used to detect ionizing radiation and high-energy particles. One important application is in medical devices, such as CT scanners.

Completing of the work

Exercise 1. Measurement of the current-voltage characteristic of a photodiode in the absence of illumination (in the dark).

When light quanta are absorbed in the p-n junction or in areas adjacent to it, new charge carriers (electrons and holes) are generated, which, passing through it, cause a voltage to appear at the photodiode terminals or a current to flow in a closed circuit. The amount by which the reverse current flowing through the junction increases is called the photocurrent.

A photodiode, depending on the material from which it is made, is used to register the light flux in the optical infrared and ultraviolet ranges. These radio components are usually made from germanium, silicon, gallium arsenide, indium, and the like.

Photodiode mode uses an external power supply to reverse bias the semiconductor device. In this case, a reverse current flows through, proportional to the light flux incident on it. In the operating voltage range (that is, before breakdown occurs), this current is practically independent of the applied reverse voltage.

In the photovoltaic mode, the photodiode acts as a sensor or as a low-current battery, since under the influence of the light flux, a voltage is generated at the terminals of the photocell, depending on the radiation flux and load.

To better understand the operating modes of this component, consider its current-voltage characteristic.

In the absence of light emission, the graph is the reverse branch of the I–V characteristic of a typical diode. There is a small return current called reverse biased dark current.

In the presence of radiation, the resistance of the photodiode decreases and the reverse current increases. The more light flux falls on the photocell, the more reverse current flows through the photodiode. The dependence in this mode is linear. As we can see from the CVC, the reverse current of the photodiode is practically independent of the reverse voltage.

Photovoltaic mode corresponds to work in the fourth quarter of the graph. And here we can distinguish two limiting options: idle and short circuit.

The mode close to idle is used to obtain energy from the photodiode, although its efficiency is low. But if you connect many such components in series and in parallel, then such a resulting battery can power a low-power circuit.

In short circuit mode, the voltage on the photocell tends to zero, and the reverse current is directly proportional to the luminous flux. This mode is used to build photo sensors.

Photodiode characteristics

In addition to the CVC discussed above, there are a number of basic parameters of the photocell.

Photodiode light characteristic, the dependence of photocurrent on illumination, which is directly proportional to the generated photocurrent on illumination. This is explained by the fact that the thickness of the base of the photodiode is much less than the diffusion length of the minority charge carriers. That is, almost all minority charge carriers that appeared in the base participate in the formation of a photocurrent.

Spectral characteristic photodiode is the dependence of the photocurrent on the wavelength of the light flux acting on the photocell.

time constant- during this time, the photocurrent of the photocell changes after illumination or after darkening of the photodiode in relation to the steady value.

dark resistance- resistance of the radio component in the absence of lighting.

A photodiode is a semiconductor diode whose current depends on the illumination. Usually, this current means the reverse current of the photodiode, because its dependence on illumination is expressed by orders of magnitude stronger than the direct current. In the future, we will talk about the reverse current.

In general, a photodiode is a p-n junction open to light radiation. Under the influence of light, charge carriers (electrons and holes) are generated in the region of the p-n junction, which pass through it and cause voltage at the terminals of the photodiode or current flow in a closed circuit.

The photodiode, depending on its material, is designed to record the light flux in the infrared, optical and ultraviolet wavelengths. Photodiodes are made from silicon, germanium, gallium arsenide, indium gallium arsenide and other materials.

Photodiodes are widely used in control systems, metrology, robotics and other fields. They are also used as part of other components, for example, optocouplers, opto-relays. With regard to microcontrollers, photodiodes are used as various sensors - end sensors, light sensors, distance sensors, pulse sensors, etc.

Designation on the diagrams

On electrical diagrams, a photodiode is referred to as a diode, with two arrows pointing towards it. The arrows symbolize the radiation incident on the photodiode. Do not confuse with the designation of the LED, in which the arrows are directed away from it.

The letter designation of the photodiode can be VD or BL (photocell).

Photodiode operating modes

The photodiode operates in two modes: photodiode and photovoltaic (photovoltaic, generator).

Photodiode mode uses a power supply that reverse biases the photodiode. In this case, a reverse current flows through the photodiode, proportional to the light flux incident on it. In the operating voltage range (that is, before breakdown occurs), this current is practically independent of the applied reverse voltage.

In photovoltaic mode, the photodiode operates without an external power supply. In this mode, it can work as sensors or as a battery (solar battery), since under the influence of light, a voltage appears on the outputs of the photodiode, which depends on the radiation flux and load.

Volt-ampere characteristics

To better understand the modes of operation of the photodiode, you need to consider its current-voltage characteristic.

The graph consists of 4 areas, the so-called quadrants. The photodiode mode corresponds to operation in the 3rd quadrant.

In the absence of radiation, the graph is the reverse branch of the current-voltage characteristic of a conventional semiconductor diode. There is a small reverse current, which is called the thermal (dark) current of the reverse-biased p-n junction.

In the presence of a light flux, the resistance of the photodiode decreases and the reverse current of the photodiode increases. The more light falls, the more reverse current flows through the photodiode. The dependence of the photodiode reverse current on the light flux in this mode is linear.

It can be seen from the graph that the reverse current of the photodiode weakly depends on the reverse voltage. Look at the slope of the graph from zero voltage to breakdown voltage, it's small.

Photovoltaic mode corresponds to the operation of the photodiode in the 4th quadrant. There are two extreme cases here:

idle (xx),
- short circuit (short circuit).

The close to idle mode is used to obtain power from the photodiode. That is, for the use of a photodiode as a solar battery. Of course, one photodiode will be of little use, and its efficiency is low. But if you connect many elements, then such a battery can power some low-power device.

In short circuit mode, the photodiode voltage is close to zero, and the reverse current is directly proportional to the light output. This mode is used to build photosensors.

What are the advantages and disadvantages of photodiode and photovoltaic modes of operation? Photodiode mode provides faster photodiode performance, but there is always dark current in this mode. In photovoltaic mode, there is no dark current, but the speed of the sensors will be slower.