Semiconductor vs Conductor vs Superconductor: How they are different?

What is a semiconductor?

Semiconductors are materials that have conductivity between conductors (generally metals) and non-conductors or insulators (such as most ceramics). Semiconductors can be pure elements, such as silicon or germanium, or compounds such as gallium arsenide or cadmium selenide. A semiconductor material has an electrical conductivity value falling between that of a conductor, such as metallic copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave the opposite.

Doping process

In a process called doping, small amounts of impurities are added to pure semiconductors causing large changes in the conductivity of the material. When two differently-doped regions exist in the same crystal, a semiconductor junction is created. The behavior of charge carriers, which include electrons, ions, and electron holes [electron hole is the absence of an electron at a position where one could exist in an atom], at these junctions is the basis of diodes [A diode is a two-terminal electronic component that conducts current primarily in one direction, it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other], transistors [A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power] and all modern electronics.

Some examples of semiconductors are silicon, germanium, gallium arsenide.

 What is band-gap

A band-gap, as you can see differentiating conductor from insulator is an energy gap in a solid where no electronic states can exist. In graphs of the electronic band structure of solids. It is generally expressed in electron volts. It is the energy required to promote a valence electron bound to an atom to become a conduction electron, which is free to move. Therefore, the band-gap is a major factor determining the electrical conductivity of a solid. Substances with large band gaps are generally insulators, those with smaller band gaps are semiconductors, while conductors either have very small band gaps or none, because the valence and conduction bands overlap.

What is a conductor?

A conductor is an object or type of material that allows the flow of charge (electrical current) in one or more directions. Materials made of metal are common electrical conductors. Electrical current is generated by the flow of negatively charged electrons, positively charged holes, and positive or negative ions in some cases.

In order for current to flow, it is not necessary for one charged particle to travel from the machine producing the current to that consuming it. Instead, the charged particle simply needs to push its neighbor a finite amount who will push its neighbor and on and on until a particle is pushed into the consumer, thus powering the machine. Essentially what is occurring is a long chain of momentum transfer between mobile charge carriers.

The five core assumptions are as follows:

[1] It ignores electron-electron and electron-ion interactions aside from collisions.

[2] It considers the metal to be formed of a collection of positively charged ions from which a number of "free electrons" were detached. These may be thought to be the valence electrons of the atoms that have become delocalized due to the electric field of the other atoms.

[3] It neglects long-range interaction between the electron and the ions or between the electrons; this is called the independent electron approximation.

[4] It considers the electrons move in straight lines between one collision and another; this is called free-electron approximation.

[5] It considers the only interaction of a free electron with its environment is collisions with the impenetrable ions core

What Is a Superconductor?

A superconductor is a substance that conducts electricity without resistance when it becomes colder than a "critical temperature."

What is this critical temperature?

The critical temperature for superconductors is the temperature at which the electrical resistivity of metal drops to zero. The transition is so sudden and complete that it appears to be a transition to a different phase of matter Several materials exhibit superconducting phase transitions at low temperatures. The highest critical temperature was about 23 K until the discovery in 1986 of some high-temperature superconductors. Materials with critical temperatures in the range of 120 K have received a great deal of attention because they can be maintained in the superconducting state with liquid nitrogen (77 K).

At the critical temperature, electrons can move freely through the material. Superconductors are different from ordinary conductors, even very good ones. Ordinary conductors lose their resistance slowly as they get colder. In contrast, superconductors lose their resistance all at once. This is an example of a phase transition. High magnetic fields destroy superconductivity and restore the normal conducting state. The superconducting state cannot exist in the presence of a magnetic field greater than a critical value, even at absolute zero. When a superconductor is cooled under the critical temperature, then it doesn’t permit the magnetic field to go through in it.

Explanation

Physicists explain superconductivity by describing what happens when temperatures get cold. The thermal energy in a solid or liquid shakes the atoms so they randomly vibrate, but this gets less as the temperature drops. Electrons carry the same negative electric charge which makes them repel each other. At higher temperatures, each electron behaves as if it were a free particle. There is also however a very weak attraction between electrons when they are in a solid or liquid.

At rather large distances (many hundreds of nanometres apart) and low temperatures (near absolute zero), the attractive effect and lack of thermal energy allow pairs of electrons to hang together, that is it acts as if it were a new kind of particle in its own right even though it is made up of two fundamental electrons. Many such overlapping can exist in the same nano-meter-sized space. All such pairs within a single superconductor synchronize and they function as if they are a single entity. They move as one entity showing no resistance to its motion. It is hence now a superconductor.

Superconductivity does not involve power loss

Superconductor principles can be explained by examining various formulas. First, lack of resistance in a current-carrying superconductor can be illustrated by Ohm's law,

R=V/I, where R is resistance, V is voltage, and I is current.

Since superconducting materials carry current with no applied voltage, R=0.

Superconductivity also does not involve power loss.

 Power is defined as P=I2R; since R is zero in a superconducting material, power loss is zero.

Superconductor materials

Unfortunately, most materials must be in an extremely low energy state (very cold) in order to become superconductive. Research is underway to develop compounds that become superconductive at higher temperatures. Currently, an excessive amount of energy must be used in the cooling process making superconductors inefficient and uneconomical.

The highest Tc reached at standard pressure, to date, is 135 °K or -138 °C by a compound (HgBa2Ca2Cu3O8) that falls into a group of superconductors known as cuprate perovskites. This group of superconductors generally has a ratio of 2 copper atoms to 3 oxygen atoms and is considered to be ceramic.

Credit: Google