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Volume 1 issue 1 (47) | ISSN: 2181-4163 | Impact Factor: 8.2
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MAGNETIC SEMICONDUCTOR MATERIALS FOR HIGH-
PERFORMANCE SPINTRONIC DEVICES
Yuldasheva Nazokatxon Murod qizi
Andijan State University Doctor of Philosophy (PhD) in Physics and math
nazokat.yuldasheva20@gmail.com
Annotation:
One of the main tasks of spintronics is the integration of magnetic
systems into semiconductor microelectronics. The easy control of electron spins in
semiconductors today allows the creation of two new classes of hybrid materials:
magnetic semiconductors (ferromagnetic/semiconductor hybrid structure) and spin-
electron nanotransistors.
Broad prospects for the application of nanoheterostructures are related to the
fact that the electronic spins of a semiconductor can be used as detectors that respond
to changes in the magnetic state in a ferromagnet. Thus, when injected through the
contact of a ferromagnet and a semiconductor, the electrons of the semiconductor will
have an unbalanced spin that contains information about the spin of the electrons in
the ferromagnet. Both optical and electrical detection methods can be used to
determine the spin direction of electrons in a semiconductor.
Key
words:
magnetic
semiconductors,
spin-electron
nanotransistors,
ferromagnetic, semiconductor, spin injectors.
Аннотация:
Одной из основных задач спинтроники является интеграция
магнитных систем в полупроводниковую микроэлектронику. Легкое
управление спинами электронов в полупроводниках сегодня позволяет создать
два новых класса гибридных материалов: магнитные полупроводники
(гибридная структура ферромагнетик/полупроводник) и спин-электронные
нанотранзисторы.
Широкие перспективы применения наногетероструктур связаны с тем, что
электронные спины полупроводника могут быть использованы в качестве
детекторов,
реагирующих
на
изменение
магнитного
состояния
в
ферромагнетике. Таким образом, при инжекции через контакт ферромагнетика
и
полупроводника
электроны
полупроводника
будут
иметь
несбалансированный спин, содержащий информацию о спине электронов в
ферромагнетике. Для определения направления вращения электронов в
полупроводнике можно использовать как оптические, так и электрические
методы обнаружения.
Ключевые слова
:
магнитные полупроводники, спин-электронные
нанотранзисторы, ферромагнетики, полупроводники, спиновые инжекторы.
International scientific journal
“Interpretation and researches”
Volume 1 issue 1 (47) | ISSN: 2181-4163 | Impact Factor: 8.2
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INTRODUCTION
However, according to many scientists and experts, in the next few decades,
without conceptual solutions, microelectronics will drastically reduce the pace of
development.
In the 21st century, one of the promising directions of the development of
microelectronics is semiconductor spintronics, which uses the charge of the electron
and its spin (internal angular momentum). Semiconductor spintronics opens up the
possibility of creating basic elements that expand the functionality of existing devices
and also allows the production of electronic devices based on new effects and
phenomena in principle (magnetoresistive memory; quantum computer; spin
transistors, valves, magnetic sensors). Spintronic devices are fast and energy efficient
because the spin of an electron can be transferred from one state to another in less
time than the transfer of energy and charge.
Since the kinetic energy of the charge carrier does not change when the spin
changes, practically no heat is released
LITERATURE ANALYSIS AND METHODOLOGY
Magnetic semiconductors.
All spintronic devices described above have in
common the fact that they are based on metal. An important disadvantage of this
approach is the inability to amplify signals. There are no exact metal analogues of
traditional semiconductor transistors today, in which the flow of electrons from the
base of the transistor allows dozens of others to flow from the emitter to the collector.
Finding materials with ferromagnetic and semiconductor properties has been a long-
standing dream of researchers. But this is difficult to achieve because there is a great
difference like chemical bonds. Ferromagnetic semiconductors, on the one hand, are
sources of spin-polarized electrons, and on the other hand, they are easily integrated
with conventional semiconductor devices.
The band structure of a magnetic
semiconductor
differs from the two-band structure of traditional semiconductors,
metals and dielectrics by the presence of a special third band formed by d- and f -
electrons of transition atoms or rare earth elements. Ideal ferromagnetic
semiconductor The conductor should have a Curie temperature above room
temperature (the temperature at which a ferromagnet loses its properties) and should
allow the formation of
n- and p-conduction bands in the crystal.
DISCUSSION AND RESULTS
Today,
much attention is being paid to the so-called alloys (GaAs), in which
individual atoms are replaced by atoms with random magnetic properties, such as
4
MoS2 transistors with 1-nanometer gate lengths / SB Desai, SR Madhvapathy, AB Sachid et al. // Science. - 2016. -
Vol. 354, No. 6308. - P. 99-102.
5
El-Aawar H. Increasing the transistor count by constructing a two-layer crystal square on a single chip / Intern. journal
of comp. science & information. tech. - 2015. - Vol. 7, No. 3. - P. 97-105.
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Volume 1 issue 1 (47) | ISSN: 2181-4163 | Impact Factor: 8.2
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dilute magnetic semiconductors containing Mn
2+.
The highest Curie temperature Tc
= 110 K has been achieved so far in GaMnAs magnetic solid solution with
p
– p-
conductivity. This material was used as a spin injector (including zero external
magnetic field) in an electroluminescent diode with a non-magnetic InGaAs/GaAs
quantum well.
Currently, the search for new ferromagnetic semiconductors with a high Curie
temperature, which can be used as spin injectors at temperatures of the order of room
temperature and in a weak (or zero) external magnetic field, is in full swing. The
most interesting results in this direction are given in which ferromagnetism is
observed at T
c = 320 K in a semiconductor with CdMn 1-x
Ge
x
P
2
chalcopyrite structure.
Figure 1.
(a) Schematic of a Johnson spin transistor, (b) Schematic of a spin-
valve transistor
Johnson spin transistor.
The development of microelectronics facilitated a
rapid transition from two-contact spin-electronic devices to three-contact systems
consisting of two ferromagnetic layers separated by a paramagnetic layer and
exhibiting a large magnetoresistance effect. Such a device was called a Johnson
transistor in honor of the inventor who connected the third contact to the
paramagnetic layer. Speaking of bipolar transistors, a Johnson transistor consists of a
base (paramagnetic), an emitter and a collector (ferromagnet). If a potential is applied
to the collector, electrons in the up/down direction are collected in the emitter-base
circuit. The collector current now depends on whether its magnetic moment is
parallel or antiparallel to the emitter magnetization. The ferromagnetic emitter in this
case plays the role of a polarizer for the collected spins. It is clear that to change the
potential in the circuit of the emitter-base, it is necessary to apply an external
6
Borisov E. Spintronics. Kuda dvigatsya dalshe? / E. Borisov // Vector high-tech. - 2013. - T. 4, No. 4. - S. 41-45.
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magnetic field, which "changes" the magnetic moment vector of the collector or
emitter in the opposite direction.
Hybrid spintronics.
The Johnson transistor is very functional, but it still has
limitations in its use. The measured voltage values are very small and cannot be
increased without the use of additional devices. The main disadvantage of such
structures is that all connections between layers are ohmic since all components of
the structure are metal.
In other words, the researchers
faced the problem of
creating a new class of structures - hybrid spin-electronic devices. Such devices
represent the combination of magnetic materials with semiconductors. Ferromagnets
polarize spins and semiconductors allow voltage blocking, current spreading and
tunneling effects.
Single transistor.
The first hybrid spin-electronic device was the Monsma
transistor, which was a spin valve sandwiched between layers of silicon. Two
contacts are connected to the silicon layers (emitter and collector), and the third is
connected to the rotary valve (base) (Fig. 5.4). The spin valve in this structure can be
composed of magnetic and non-magnetic metal layers that are repeated over and over
again. At the interfaces between silicon and metal, Schottky barriers are formed that
absorb bias voltages applied between pairs of contacts (Fig. 5.5). The collector
Schottky barrier is reverse biased, while the emitter barrier is forward biased. This
allows unpolarized "hot" electrons from the semiconductor emitter to be sent to the
metal base with energies higher than the Fermi energy. The question is: can hot
electrons pass through the spin valve and retain enough energy to overcome the
Schottky barrier of the collector? Otherwise, they remain in the base and go to the
outer circuit. By changing the magnetic configuration of the base, you can determine
how much energy the "hot" electrons lose as they pass through the base. If the
magnetic moments of adjacent spin valve layers are antiferromagnetically aligned,
then both types of spin are equally distributed in the magnetic layers. If an external
magnetic field is applied to the spin valve, which equalizes all the magnetic moments
of the layers, then one type of spin (spin down or "minor") is strongly propagated,
while the other (spin or "major") passes through the entire magnetic structure without
propagation.
7
Danilov Yu.A. Magnetic semiconductor nanostructures for spintronic devices / Yu.A. Danilov // Prilozhenie k journal
"Vestnik RGRTU". - 2009. - No. 4. - S. 1-6.
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(a) ( b )
Figure 2. (a) Working principle of SFET, (b) schematic diagram (top)
and
energy diagram (bottom) of the spin blocking device.
Datta-Das spin field effect transistor (SFET).
In 1990, Supriyo Datta and
Biswajit Das considered the possibility of creating a spin field effect transistor based
on the relativistic effect. The device has a design similar to a conventional field-effect
transistor with source and drain contacts (ferromagnets) and a gate (semiconductor).
Spin-polarized carriers leave the source with spins and precession parallel to the
magnetization of the ferromagnet when moving due to the Rashba effect (Fig. 2). In
this case, electrons must move at a speed of 1% of the speed of light in a vacuum.
With sufficient magnetic field strength (in this case, the speed of the electron is very
important), the electron spins reverse direction. As a result, the channel resistance
increases and the current decreases. By changing the gate potential, the conductance
of the device can be changed. This device works like a traditional field-effect
transistor, its peculiarity is that the differential magnetization of the contacts ( and
therefore its electrical properties) is sensitive to the external magnetic field.
New effects in spintronics: spin blockade.
At the end of the last century, a new
effect was found in the device, the diagram of which is shown in Fig. 2. The spin
blocking system consists of cobalt contacts, between which are ferromagnetic cobalt
islands, which change the direction of magnetization under the influence of an
external magnetic field. For example, Figure 2 shows a Schottky barrier at low
temperature, which blocks circuits in such a device. The magnitude of the
magnetoresistive effect remains 25% at T = 20 K, which is unprecedented for silicon-
based devices. The network structure consists of a Schottky barrier, along the edges
of which there are a number of magnetic islands, between which an antiferromagnetic
coupling is established ( and therefore, in the absence of an external magnetic field, o
'blocks tooth spins).
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In a magnetic field, the magnetization vectors of the islands are directed across
the field, and the resistance of the structure decreases due to tunneling between
adjacent islands. Exposure to optical radiation increases the resistance of the
structure, as photons activate the electrons of the islands, increasing the density of
energy states. The geometry of such a system is not much different from a high
electron mobility transistor, in which the conductance of the main current channel is
controlled by localized states in adjacent but physically separated regions of the
device.
References:
1. MoS2 transistors with 1-nanometer gate lengths / SB Desai, SR
Madhvapathy, AB Sachid et al. // Science. - 2016. - Vol. 354, No. 6308. - P. 99-102.
2. El-Aawar H. Increasing the transistor count by constructing a two-layer
crystal square on a single chip / Intern. journal of comp. science & information. tech.
- 2015. - Vol. 7, No. 3. - P. 97-105.
3. Borisov E. Spintronics. Kuda dvigatsya dalshe? / E. Borisov // Vector high-
tech. - 2013. - T. 4, No. 4. - S. 41-45.
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5. Danilov Yu.A. Magnetic semiconductor nanostructures for spintronic devices
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