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Applications of Modern Physics in Electronics Content Solid State Physics Diodes Transistors Biopolar Junction Transistor(BJT) Metal Oxide Field Effect Transistor (MOSFET) Capasitor Lasers Quantum Computers Difficulties in Quantum Computers Conclusion 1

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Applications of Modern Physics in Electronics

Content

Solid State Physics

Diodes

Transistors

Biopolar Junction Transistor(BJT)

Metal Oxide Field Effect Transistor (MOSFET)

Capasitor

Lasers

Quantum Computers

Difficulties in Quantum Computers

Conclusion

Index

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Applications of Modern Physics in Electronic Engineering

Solid State Physics:

It is not possible to have many technological devices without taking advantage of the basics of the solid state physics and its applications.Solid state theory investigates the crystals of the matter because electrical,magnetic,optical and mechanical properties are importat for several engineering branches. As it is known that, the basis of many electronical devices were also created using the solid state theory.In this project ,especially, the basis of solid state theory will be discussed in terms of the electronical engineering. Basically,solid state electorinic meratials could be defined as semiconductors ,conductors and insulators. Generally,semicoductors are made  silicon, germanium, and gallium arsenide .Some of the most important semiconductor devices are diodes, transistors,IC circuits (integrated circuits), microprocessors,rams and so on. These semiconductor devices have changed the face of electronics today and our lifes.They are in our daily lifes all the time in our computers,smartphones and many that could not be counted. Semiconductors are exactly what the name implies therefore they have both the properties of a conductor and insulator.In order to understant the how this is possible,the only thing could be count on is modern physics. It could help to visualise complexity of working principals of semiconductor devices. Semiconductors consist of the properties of conductors and insulators as it is indicated above. In order to have the conducting properties a process required called doping.it is used to change the configuration of the atom that makes up the semiconductor material.Most semiconductors have a crystalline structure and by adding a n type doping into the material, which is essentially an impurity, the conductive properties of the semiconductor could be increased and opposite p type.Usage of p-n semiconductors are more common more useful  to control the location and concentration of p- and n-type dopants. Diodes:

The forward-bias and the reverse-bias properties of the p–n junction imply that it could be used as a diode. A p–n junction diode allows electric charges to flow in one direction, but not in the opposite direction; negative charges (electrons) could easily flow through the junction from n to p but not from p to n, and the reverse is true for holes. When the p–n junction is forward-biased, electric charge flows freely due to reduced resistance of the p–n junction. When the p–n junction is reverse-biased, however, the junction barrier (and therefore resistance) becomes greater and charge flow is minimal.

Semiconductors helps us to get precise control over the flow of current through a system. For example,diodes are among the simplest electronic components available and they are manufactured using semiconductors. Diodes will permit electricity to flow through them in one direction, but not in the other. The most common and basic application of diode is actually LED’s, which stands for light emmitig diode.

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The p-n type semiconductor diode shown in the figure below;

Figure 1. p-n type diode structure

Transistors: Secondly,transistors is a great example of semiconductor based electronical devices in modern age.As it is know , the microprocessors builds by using enourmous amount of transistors locaded on the silicone chip.Microprocessors utilize transistors to perform the many functions for which they are used.

Biopolar Junction Transistor (BJT):

Bipolar junction transistors are available as PNP as well as NPN devices.The difference between npn and pnp transistors is the polarity of the base emitter diode junctions, as shown by the direction of the schematic symbol emitter arrow. It points in the same direction as the anode arrow for a junction diode, against electron current flow. The point of the arrow and bar correspond to P-type and N-type semiconductors, respectively. For NPN and PNP emitters, the arrow points away and toward the base respectively. There is no schematic arrow on the collector. However, the base-collector junction is the same polarity as the base-emitter junction compared to a diode.

Figure 2 .NPN –PNP Biopolar Junction Transistors

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Metal Oxide Field Effect Transistor (MOSFET):

Today, most transistors are of the metal oxide field effect transistor (MOSFET) type as components of digital integrated circuits.MOSFET transistors also uses the basics of semiconductors.Usually,MOSFET’s are made using silicondioxide but nowadays they could also be produced using a chemical compound of silicon-germanium (SiGe). As the silicon dioxide is a dielectric material, its structure is equivalent to a planar capacitor, with one of the electrodes replaced by a semiconductor.

Figure 3.Metal Oxide Field Effect Transistor

The channel could contain electrons (called NMOS), or holes (called a PMOS), opposite in type to the substrate, so NMOS is made with a p-type substrate, and PMOS with an n-type substrate. 

Semiconductors could be used to create anything from simple amplifiers to more complex circuits to sophisticated supercomputers.Thus far, there have been few limits that have been hit utilizing semiconductor technology.In the future ,semiconductors will increase the capabilities of the technology than we have now.

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Figure 4. An Overview of Semiconductors in Electronics

Capasitors:

It would be neccessery to indicate the how capasitors are made using the solid state physics.Firstly,dielectric consept should be defined.A dielectric meterial is an electirical insulator that could be polarized by an applied electric field. The term insulator is generally used to indicate electrical obstruction while the term dielectric is used to indicate the energy storing capacity of the material.

The basic definition of a capasitor is, when a dielectric is placed between two plates the electric is charged as an electrostatic field as shown in the figure below;

Figure 5.Capasitor

Lasers:

Another application of solid state physics in electronics is lasers which is acronym of light amplification by stimulated emission of radiation.It is a device that utilizes the natural oscillations of atoms or molecules between energy levels for generating a beam of coherent electromagnetic radiation usually in the ultraviolet, visible, or infrared regions of the spectrum.It has to be indicated that Einstain’s stimulated emission theory was the fundemental of the laser technology.The basic theory of laser is invetigated above;

Quantum mechanics claims that light is composed of many quanta of energy “ photons”. It also indicates that electrons in an atom are only allowed to have certain discrete energies. Consider a photon and a simple atom that only has two energy levels ,the photon and the atom (electron) could interact in three different ways: Absorption , Spontaneous emission, Stimulated emission.

When light is absorbed by an atom, it is excited into a higher energy state. Quantum mechanics only allows transitions to certain energy levels, so only photons of particular energies could be absorbed (and emitted).

Spontaneous emission occurs when an atom is in an excited state and emits a photon in order to go back to the preferred lower energy level.It is known that nature prefers to minimize energy.In this

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case, an atom in an excited state is not stable, it tries to find a way of getting back to its ground state eventually.

Stimulated emission occurs when you have an atom in an excited state and it interacts with a photon that, ideally, has an energy that is identical to the transition energy between the atom’s current state and a lower energy state. The atom’s response is to emit a photon that is exactly identical to the incident photon.If one quantum of light send, then two quantum light will be obtained. This is the fundamental phenomenon that gives us lasers.

The following figure shows the basic theory of producing laser.

Figure 6. Laser Theory

After the brief information about laser theory above ,let us examine the lasers in electonics pont of view.There are many types of lasers that could be used for different purposes like cutting ,reading ,scanning ,marking and etching which means, lasers have many applications including medicine, scientific,military,nucleer fusion ,fiber optics and so on.In order to more focus on the relation between the physcis and its aplicaions in electronics it is better to mention the laser diodes.

A laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common type of laser diode is formed from a p-n junction and powered by injected electric current.These are very new and trendy lasers which use the techniques of making computer chips to make tiny lasers out of silicon and other semiconductors.

The most common laser diode generates semiconductor or injection laser. In these lasers, a population of inversion electrons is produced by applying a voltage across its p-n junction. Laser beam is then available from the semiconductor region. The p-n junction of laser diode has polished ends so that, the emitted photons reflect back and forth and creates more electron-hole pairs. The photons thus generated will be in phase with the previous photons. This will give us a pencil beam and all the photons in the beam are coherent and in phase.

When we compared the semiconductor lasers to other types of lasers, semiconductor lasers are compact, reliable and capable of long term use.Such lasers consist of two basic components, an optical amplifier and a resonator. The amplifier is made from a direct-bandgap semiconductor material based on generally galliumarsenide “GaAs” and InP “indium phosphide” substrates. These are compounds based on the Group III and Group V elements in the periodic table.Alloys of these

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materials are formed onto the substrates as layered structures containing precise amounts of other materials. The resonator continuously recirculates light through the amplifier and helps to focus it. This component usually consists of a waveguide and two plane-parallel mirrors.These mirrors are covered by a material to increase or decrease reflectivity and to improve resistance to damage from the high power densities.

The performance and cost of a semiconductor depends on its output power, brightness, and operating lifetime. Power is important because it determines the maximum throughput or feed rate of a process. High brightness, or the ability to focus laser output to a small spot, determines power efficiency. Lifetime is important because the longer a laser lasts, the less it costs to operate, which is especially critical in industrial applications.The simplest semiconductor lasers consist of a single emitter that produces over one watt of continuous wave power. To increase power, bars and multibar modules or stacks have been developed. A bar is an array of 10 to 50 side-by-side individual semiconductor lasers integrated into a single chip and a stack is a two-dimensional array of multiple bars. Bars could produce 50 watts of output power and ends over 5,000 hours

Figure 7. Laser

Laser diodes could be switched on and off at frequencies as high as 1GHz, making them ideal in telecommunication applications. Since laser generates heat on hitting the body tissue, it is an ideal solution to heal sensitive parts like retina of eye and brain. Laser could be used to pinpoint the lesions so that nearby tissues are not affected as in the case of surgery.

Figure 8. Laser Diode

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The small circle in the figure above ,it could be seen that the laser diode is plased into a DVD player.Quantum Computers:

Quantum computer is a device which uses the principles of quantum physics to increase the computational power beyond what is attainable by a traditional computer. Quantum computers have been built on the small scale and work continues to upgrade them to more practical models.

Computers function by storing data in a binary number format, which result in a series of 1s and 0s retained in electronic components such as transistors.Each component of computer memory is called abit and could be manipulated through the steps of  Boolean Logic so that the bits change, based upon the algorithms applied by the computer program, between the 1 and 0 modes.

Figure 9. A Quantum Chip

Let us consider if such computer produced, how it would be work. A quantum computer would store information as either a 1, 0, or a quantum superposition of the two states. Such a "quantum bit," called a qubit , allows for far greater flexibility than the binary system.

Specifically, a quantum computer would be able to perform calculations on a far greater order of magnitude than traditional computers. Some peoples belives that quantum computers would destroy the world's financial system by ripping through their computer security encryptions, which are based on factoring large numbers that literally could not be cracked by traditional computers within the lifespan of the universe. A quantum computer could factor the numbers in a reasonable period of time.

In order to understand how this speed works in quantum device, let us consider this example. If the qubit is in a superposition of the 1 state and the 0 state, and it performed an calculation with another qubit in the same superposition, then one calculation actually obtains 4 results: a 1/1 result, a 1/0 result, a 0/1 result, and a 0/0 result. This is a result of the mathematics applied to a quantum system when in a state of decoherence, which lasts while it is in a superposition of states until it collapses down into one state. The ability of a quantum computer to perform multiple computations simultaneously. The exact physical mechanism at work within the quantum computer is somewhat theoretically complex and intuitively disturbing. Generally, it is explained in terms of the multi-world

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interpretation of quantum physics, wherein the computer performs calculations not only in our universe but also in other universes simultaneously, while the various qubits are in a state of quantum decoherence.

A handful of quantum computers have been built. The first, a 2-qubit quantum computer in 1998, could perform trivial calculations before losing decoherence after a few nanoseconds. In 2000, teams successfully built both a 4-qubit and a 7-qubit quantum computer. Research on the subject is still very active, although some physicists and engineers express concerns over the difficulties involved in upscaling these experiments to full-scale computing systems. Still, the success of these initial steps to show that the fundamental theory is strong.

Figure 10. Comparison between Clasical bits and Qubit

Difficulties in Quantum Computers:

The main disadvantages of quantum computers is quantum decoherence. The qubit calculations are performed while the quantum wave function is in a state of superposition between states, which is what allows it to perform the calculations using both 1 and 0 states simultaneously.As a solution, a quantum computer must be totally isolated from all external interference during the computation phase. Some success has been achieved with the use of qubits in intense magnetic fields, with the use of ions.

However, when a measurement of any type is made to a quantum system, decoherence breaks down and the wave function collapses into a single state. Therefore, the computer has to somehow continue making these calculations without having any measurements made until the proper time, when it could then drop out of the quantum state, have a measurement taken to read its result, which then gets passed on to the rest of the system.

The physical requirements of manipulating a system on this scale are considerable, touching on the realms of superconductors, nanotechnology and quantum electronics, as well as others. Each of these is itself a sophisticated field which is still being fully developed.

Even though there are many problems to overcome, the breakthroughs in the last 15 years,have made some form of practical quantum computing not unreachable but it is a open question that how much time is needed. However, the potential that this technology offers is attracting enormous interest from both the government and the private sector. Military applications include the ability to break encryptions keys via brute force searches, while civilian applications range from DNA

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modeling to complex material science analysis. It is this potential that is rapidly breaking down the barriers to this technology, but whether all barriers could be broken, and when, is very much an open question.

Conclusion:

In counclusion,it has been indicated that,the applications of physics is around us all the time. When it is look the inside of electronics devices with the light of physics, it could be eaisly seen that there is a powerful physics theories lies behind.The substructures of electronic devices are investigated and what found is the Solid State Physics.It is one of the most importat theory that used in all of the electronic devices.The study of theoretical physics especially the solid state physics, allows us to understand, in a deeper way, the field of electronics at the atomic level. It is an enhancement to the study of electronics.

Let us consider this example to make it more clear,a person could be trained in electronics without being trained in physics.They could design,built and provide innovative electronic devices.It could be also possible that they could discover new components like many electrician in the past.However,on the other hand,in order to understand how the components work exactly and suggest other materials that might work better ,it is all required to know the physics.

The procedure works like ,a physical phenomenon is observed in a laboratory, described mathematically, improved, and then used in a practical circuit by electronic engineers combining it with pre-existing components through the use of mathematics.Transistors,microchips and capasitors could be great example of this process.

To summarize,electronics is the study of the practical application of existing devices through the use of their observed mathematical descriptions and physics is the study of the interaction of matter and energy, and the mathematical description of the process.

Figure 11. An Integrated Circuit Built by Silicone

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