VALVE PHOTO EFFECT
photoelectric effect in the barrier layer - occurs under the influence of electromagnetic radiation electromotive force(photovoltage) in a system consisting of two contacting different PP or PP and metal. The greatest practical of interest is F. v. in the p-i transition and heterojunction. F.v. used in photovoltaics. generators, in PP photodiodes, phototransistors etc.
. 2004 .
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Quantum mechanics ... Wikipedia
Redistribution of electrons according to energy. states in solid and liquid PP and dielectrics, occurring under the influence of electromagnetism. radiation. F.v. is detected, as a rule, by a change in the concentration of current carriers in the medium, i.e. by the appearance of... Big Encyclopedic Polytechnic Dictionary
valve photoelectric effect- Internal photoelectric effect, in which emf occurs. [Collection of recommended terms. Issue 79. Physical optics. Academy of Sciences of the USSR. Committee of Scientific and Technical Terminology. 1970] Topics: physical optics General terms transformation... ... Technical Translator's Guide
PHOTO EFFECT, a group of phenomena associated with the release of electrons of a solid body from intra-atomic bonds under the influence of electromagnetic radiation. There are: 1) external photoelectric effect, or photoelectron emission, the emission of electrons from the surface... ... Modern encyclopedia
A phenomenon associated with the release of electrons from a solid (or liquid) under the influence of electromagnetic radiation. There are:..1) external photoelectric effect, the emission of electrons under the influence of light (photoelectron emission), ? radiation, etc.;..2)… … Big Encyclopedic Dictionary
PHOTO EFFECT- (1) valve generation of electromotive force (photoEMF) between two dissimilar semiconductors or between a semiconductor and a metal under the influence of electromagnetic radiation; (2) F. external (photoelectron emission) emission of electrons with ... Big Polytechnic Encyclopedia
A; m. Phys. Changes in the properties of a substance under the influence of light energy; photoelectric effect. * * * photoelectric effect is a phenomenon associated with the release of electrons from a solid (or liquid) under the influence of electromagnetic radiation. Distinguish:... ... Encyclopedic Dictionary
valve photoelectric effect
photoelectric effect of the barrier layer- užtvarinis fotoefektas statusas T sritis fizika atitikmenys: engl. barrier layer photoeffect; barrier layer photoelectric effect; photovoltaic effect vok. Sperrschichtphotoeffekt, m rus. gate photoelectric effect, m; photovoltaic effect, m;… … Fizikos terminų žodynas
A phenomenon associated with the release of TV electrons. body (or liquid) under the influence of electricity. mag. radiation. They distinguish: ext. Ph. emission of electrons under the influence of light (photoelectron emission), y radiation, etc.; internal F. increase... ... Natural science. Encyclopedic Dictionary
Essence valve photoelectric effect, or photoelectric effect in the barrier layer is that, due to the internal photoelectric effect, a potential difference arises near the contact between a metal and a semiconductor or between semiconductors - and type. In Fig. Figure 2.4 shows a diagram of a gate photocell.
A layer of semiconductor 2 is applied to the metal electrode 1, covered with a thin translucent layer of gold 4, and a metal ring 5, which serves as an electrode, is tightly pressed to it. Between the semiconductor and the gold layer, an intermediate layer 3 appears, which has the property of passing electrons in only one direction - from the semiconductor to gold. If the - transition is illuminated with light, additional charge carriers appear in the area of contact of two semiconductors (or gold and semiconductor) (electrons in - areas and holes in the area) that pass through the transition quite easily. As a result, an excess positive charge is formed in the -region, and an excess negative charge is formed in the region. The potential difference that arises at the contacts of these semiconductors when quanta of electromagnetic radiation are absorbed in it is called photoelectromotive force (photo-EMF). If such a sample is included in a closed circuit, an electric current will arise, which is called photocurrent. The value of photo-EMF at low light fluxes is proportional to the flux incident on the crystal. The action of solar panels is based on the phenomenon of the valve photoelectric effect. They represent from several tens to several hundred thousand elements of silicon junctions connected in series. Solar panels convert light energy directly into electrical energy. Due to their initial high cost, they began to be used mainly on spacecraft. Solar energy is one of the most important areas in the development of the energy sector of the future. This is the most promising way to obtain and use energy on Earth. Although this is still an expensive form of energy, in the future its cost will be comparable to that produced at nuclear power plants. Moreover, such energy is environmentally friendly and its reserves are practically inexhaustible. Nowadays, energy production using solar panels is carried out on an industrial scale, and research is being conducted around the world to increase the power of solar photovoltaic installations. According to experts, in 2020, up to 20% of the world's electricity will be produced through photovoltaic conversion of solar energy and used in transport, mechanical engineering, instrument making, medicine, space and other industries. The prospects for the development of solar energy are evidenced by the following fact: if in 1985 the entire installed capacity of solar power plants in the world was 21 MW, then in 2010 the total capacity of photovoltaic stations reached 40,000 MW, i.e. over 25 years, the capacity of power plants generating electricity using photovoltaic converters has increased approximately 2000 times.
There are external internal and valve photoeffects. The external photoelectric effect (photoelectric effect) is the emission of electrons by a substance under the influence of electromagnetic radiation. The external photoelectric effect is observed in solids(metals, semiconductors, dielectrics), as well as in gases and individual atoms and molecules (photoionization). The photoelectric effect was discovered (1887) by G. Hertz, who observed the force of the discharge process when the spark gap was irradiated with ultraviolet radiation.
First basic research photoelectric effect were performed by the Russian scientist A.G. Stoletov. Two electrons (cathode K made of the metal under study and anode A in Stoletov’s scheme, a metal mesh was used) in a vacuum tube are connected to the battery so that using potentiometer R you can change not only the values, but also the sign of the voltage applied to them. The current generated when the cathode is illuminated with monochromatic light (through a quartz window) is measured by a milliammeter connected to the circuit. By irradiating the cathode with light of various wavelengths, Stoletov established the following patterns that have not lost their meaning to this day:
1. Ultraviolet radiation has the most effective effect.
2. When exposed to light, a substance loses only negative charges.
J.J. Thomas in 1898 measured the charge of particles emitted under the influence of light (by deviation in electrical and magnetic fields). These measurements showed that electrons were produced when exposed to light.
Internal photoelectric effect
The internal photoelectric effect is a free transition of electrons inside a semiconductor or dielectric from bound states caused by electromagnetic radiation without escaping outside. As a result, the concentration of current carriers inside the body increases, which leads to the occurrence of photoconductivity (an increase in the electrical conductivity of a photoconductor or dielectric when illuminated) or the appearance of emf.
Valve photoeffect
Valve photoelectric effect - emf (photo-emf) occurs when the contact of two different semiconductors or a semiconductor and a metal is illuminated (in the absence of external electric field). The valve photoelectric effect thus opens the way for the direct conversion of solar energy into electrical energy
Current-voltage characteristics of the photoelectric effect
The current-voltage characteristic of the photoelectric effect is the dependence of the photocurrent I generated by the flow of electrons emitted by the cathode under the influence of current on the voltage U between the electrodes. This dependence corresponds to two different illumination E e of the cathode (the light frequency is the same in both cases). As U increases, the photocurrent gradually increases, i.e. an increasing number of photoelectrons reach the anode. The flat nature of the curves shows that electrons are emitted from the cathode at different speeds. The maximum value of the current I us - saturation photocurrent - is determined by the value of U at which all electrons emitted by the cathode reach the anode.
From the current-voltage characteristic it follows that at U = 0 the photocurrent does not disappear. Consequently, electrons knocked out of the cathode by light have a certain initial speed v, and therefore non-zero kinetic energy, and can reach the anode without an external field. In order for the photocurrent to become zero, it is necessary to apply a delay voltage U 0 . At U = U 0, none of the electrons, even those with the maximum speed v max when leaving the cathode, can overcome the retarding field and reach the anode. Hence,
Where n is the number of electrons emitted by the cathode per 1s.
mv 2 max /2= e U 0
those. By measuring the restraining voltage U0, it is possible to determine the maximum speed and kinetic energy photoelectrons.
When emitting current-voltage characteristics of various materials (the frequency of the surface is important, therefore measurements are carried out in a vacuum and on fresh surfaces) at different frequencies of radiation incident on the cathode and different energy illuminations of the cathode and generalizing the data obtained, the following three laws of the external photoelectric effect were established.
Gate photoEMF - EMF resulting from the spatial separation of electron-hole pairs generated by light in a semiconductor by an electric field transition n, heterojunction, near-electrode barrier. With the valve photoelectric effect, an electric field is not applied to the photocell, since they themselves are generators of photoEMF. Characteristic feature photocells with a gate photoeffect is the presence of a blocking layer between the semiconductor and the electrode, which causes the rectifying effect of this layer (Fig. 1.17).
The semiconductor layer with a gate photoeffect has not only resistance, but also capacitance and is a rectifier and source of emf when illuminated with light. In Fig. 1.17 Cu plate (4) is one of the electrodes. On top it is covered with a thin layer (2) of copper oxide Cu 2 0 due to the heating of copper in air at a high temperature. The barrier layer (3) is formed at the interface between Cu 2 0 and copper. A thin translucent layer of gold is applied on top (1). When illuminated, a potential difference arises between electrodes 1 and 4.
| Rice. 1.17 |
If these electrodes are connected through a galvanometer, then when light is incident, a photocurrent appears, directed from copper to Cu 2 0. The photoconductivity of cuprous oxide photocells is caused by the movement of holes. A thin blocking layer (d » 10 - 7 m) at the metal-semiconductor interface causes the blocking effect of the photocell and the appearance of photovoltage up to 1 V. In this case, the radiant energy of light is directly converted into electrical energy. Photocell efficiency ~2.5%.
Compton effect
The Compton phenomenon consists of an increase in the wavelength of X-rays when they are scattered by atoms of a substance, which is accompanied by a photoelectric effect. From a classical point of view wave theory The wavelength of the scattered radiation must be equal to the wavelength of the incident radiation.
The scheme of Compton's experiment is shown in Fig. 1.18, where S is the x-ray source; D 1 and D 2 - diaphragms that form a narrow beam of X-rays; A is a substance that scatters X-rays, which then fall on the spectrograph C and the photographic plate F.
The Compton phenomenon is characterized by the following patterns:
1. Depends on the atomic number of the substance. 2. As the scattering angle increases, the intensity of Compton scattering increases. 3. The wavelength shift increases with increasing scattering angle.
4. At the same scattering angles, the wavelength shift is the same
When an X-ray photon interacts with an electron, the latter receives energy (W) and momentum (p = mv) leaves the atom (recoil electron), and the energy and momentum of the scattered photon decrease (Fig. 1.19).
To find the change in wavelength of a scattered photon in the Compton effect, we apply the law of conservation of momentum
and the law of conservation of energy
W f + W 0 = W + ,
Where total energy particles
.
From the law of conservation of momentum we find the momentum of the particle (electron).
For example, according to Fig. 1.19 (cosine theorem)
Taking into account the relativistic nature of motion for the photon, we have
W f = hn= r f s.
Taking this into account, we represent the law of conservation of energy in the form
Solving (6.18) and (6.19) together and after squaring we get
, (1.34)
(1.35)
Pulses of incident and scattered photons; j - scattering angle;
c is the speed of light; h is Planck's constant.
Using the relationship between wavelength and frequency in the form:
And
Internal photoelectric effect- are caused by electromagnetic radiation electron transitions inside semiconductor or dielectric from bound states to free ones without flying out. As a result, the concentration of current carriers inside the body increases, which leads to the occurrence of photoconductivity - an increase in the electrical conductivity of a semiconductor or dielectric when illuminated.
Valve photoeffect (a type of internal photoeffect)
1. the occurrence of EMF (photo-EMF) when illuminating the contact of two different semiconductors or a semiconductor and a metal (in the absence of an external electric field). The gate photoelectric effect is used in solar cells to directly convert solar energy into electrical energy.
External photoelectric effect (photoelectron emission) is the emission of electrons by a substance under the influence of electromagnetic radiation.
Scheme for studying the external photoelectric effect. Two electrodes (cathode K from the metal under study and anode A) in a vacuum tube are connected to the battery so that you can change not only the value, but also the sign of the voltage applied to them. The current generated when the cathode is illuminated with monochromatic light (through a quartz window) is measured by a milliammeter connected to the circuit. Photocurrent dependence I, formed by the flow of electrons emitted by the cathode under the influence of light, from voltage U between the cathode and the anode is called the current-voltage characteristic of the photoelectric effect.
As U increases, the photocurrent gradually increases until it reaches saturation. Maximum current value I us - saturation photocurrent - is determined by this value U, in which all electrons emitted by the cathode reach the anode: I us = en, Where n- the number of electrons emitted by the cathode in 1s. When U = O photocurrent is not
disappears, since photoelectrons, when leaving the cathode, have a certain initial speed. In order for the photocurrent to become zero, it is necessary to apply a delay voltage U 0 . At U = U 0, none of the electrons, even those with the maximum initial speed upon departure, can overcome the retarding field and reach the anode:
i.e., by measuring the delay voltage U 0, you can determine the maximum speed value υ max and kinetic energy K m ax of photoelectrons.
45. Laws of the photoelectric effect.
(1) Stoletov's Law: at a fixed frequency of incident light, the number of photoelectrons emitted by the photocathode per unit time is proportional to the light intensity (the strength of the saturation photocurrent is proportional to the irradiance E e of the cathode).
(2) The maximum initial speed (maximum initial kinetic energy) of photoelectrons does not depend on the intensity of the incident light, but is determined only by its frequency ν
(3) For each substance there is a red limit of the photoelectric effect - the minimum frequency of light (depending on chemical nature substance and the state of its surface), below which the photoelectric effect is impossible.
To explain the mechanism of the photoelectric effect, Einstein suggested that light with frequency ν is not only emitted by individual quanta (according to Planck’s hypothesis), but also propagates in space and is absorbed by matter in individual portions (quanta), the energy of which is ε 0 = hν.
Quanta of electromagnetic radiation moving at the speed of light propagation in a vacuum are called photons.
The energy of the incident photon is spent on the electron performing the work of exit A from the metal (see p. 3-31) and on imparting kinetic energy to the emitted photoelectron. Einstein's equation for the external photoelectric effect:
This equation explains the dependence of the kinetic energy of photoelectrons on the frequency of incident light (2nd law). Limit frequency
(or ), at which the kinetic
the energy of photoelectrons becomes zero, and there is a red limit of the photoelectric effect (3rd law). Another form of writing the Einstein equation 
The figure shows the dependence of the maximum kinetic energy of photoelectrons on the frequency of irradiating light for aluminum, zinc and nickel. All straight lines are parallel to each other, and the derivative d(eU 0)/dv does not depend on the cathode material and is numerically equal to Planck’s constant h. The segments cut off on the ordinate axis are numerically equal to the work A release of electrons from the corresponding metals.
The effect of photocells and photoresistors (photoresistors) in photoexposure meters, lux meters and control and automation devices for various processes, consoles is based on the phenomenon of the photoelectric effect. remote control, as well as semiconductor photomultiplier tubes and solar cells.
The existence of photons was demonstrated in Bothe's experiment. A thin metal foil F, located between two Sch counters, emitted X-rays under the influence of hard irradiation. If the emitted energy were distributed evenly in all directions, as follows from wave concepts, then both counters would have to operate simultaneously, and synchronous marks with markers M would appear on the moving belt A. In reality, the location of the marks would be random. Consequently, in separate acts of emission, light particles (photons) are born, flying in one direction or another.
46. Mass and momentum of a photon. Unity of corpuscular and wave properties of light.
Using the relations, we obtain expressions for the energy, mass and momentum of the photon
These relationships connect the quantum (corpuscular) characteristics of a photon - mass, momentum and energy - with the wave characteristic of light - its frequency.
Light has at the same time wave properties that manifest themselves in the patterns of its propagation, interference, diffraction, polarization, and corpuscular, which manifest themselves in the processes of interaction of light with matter (emission, absorption, scattering).
47. Light pressure.
If photons have momentum, then light falling on a body must exert pressure on it.
Let the flux of monochromatic frequency radiation fall perpendicular to the surface. If N photons fall on 1 m 2 of the surface of a body in 1 s, then with a reflection coefficient p of light, ρ will be reflected from the surface of the body N photons, and (1-ρ) N photons - will be absorbed. Each absorbed photon transfers momentum to the surface p γ, and each reflected photon is -2 p γ
The light pressure on the surface is equal to the impulse transmitted
surfaces in 1s N photons
Energy illumination of a surface (the energy of all photons incident on a unit surface per unit time). Volumetric
radiation energy density: . From here 
The wave theory of light, based on Maxwell's equations, comes to the same expression. The pressure of light in the wave theory is explained by the fact that under the influence of an electric field
electromagnetic wave, the electrons in the metal will move in the direction (indicated
in the picture) opposite
Magnetic field
An electromagnetic wave acts on moving electrons with a Lorentz force in the direction (according to the left-hand rule) perpendicular to the surface of the metal. Thus, electromagnetic wave exerts pressure on the metal surface.
48. Compton effect.
The corpuscular properties of light are clearly manifested in the Compton effect - elastic scattering of short-wave electromagnetic radiation (X-rays and -radiations) on free (or weakly bound) electrons of a substance, accompanied by an increase in wavelength. This increase does not depend on the wavelength λ of the incident