semiconductor

Basic Principles

Semiconductors are the basic elements of electronics components such as diodes, transistors and an IC (integrated circuit). Called semi-or half-conductors, since this material is not a pure conductor. Metals such as copper, iron, tin referred to as a good conductor because the metal has an atomic arrangement is such that electrons can move freely. 

Atomic Structure of Semiconductors

Semiconductor materials are widely known example is Silicon (Si), Germanium (Ge) and Gallium arsenide (GaAs). Germanium is a material previously only known for making semiconductor components. But lately, silicon became popular after it was discovered how to extract these materials from nature. Silicon is the second largest material on earth after oxygen (O2). Sand, glass and other stones are natural materials that contain many elements of silicon. Can you calculate the amount of sand on the beach.
Crystalline structure of silicon atoms, one atom core (nucleus) each have 4 valence electrons. Nuclei are stable bond is when surrounded by 8 electrons, so the 4 pieces of crystal atomic electrons form a covalent bond with neighboring atomic ions. At very low temperatures (0oK), the atomic structure of silicon visualized as shown below.

two-dimensional structure of crystalline silicon
 

Covalent bond causes the electrons can not move from one nucleus to another nucleus. In such conditions, semiconductor materials are insulators because the electrons can not move to conduct electricity. At room temperature, there are some covalent bonds are loose due to heat energy, thus allowing the electrons released from this bond. However, only some small amount that can be detached, so it is not possible to be a good conductor.
Physicists, especially the control of quantum physics at that time was trying to give this doping in semiconductor materials. The provision is intended to get a doping-free valence electrons in much smaller lots and permanent, which will hopefully be able to conduct electricity. In fact such, they are fun once and a genius.

Type-N

For example on a silicon material given doping phosphorus or arsenic pentavalen the crystalline material with atomic nuclei has 5 valence electrons. With doping, silicon is no longer pure (impurity semiconductor) will have an excess of electrons. Excess electrons to form n-type semiconductors. N-type semiconductor is also called a donor ready to release electrons.

doping atoms pentavalen
 

Type-P

If silicon were doped Boron, Gallium or Indium, it will be obtained p-type semiconductor. To obtain p-type silicon, the material is a material dopingnya with trivalent ions of elements which has 3 electrons in the valence band. Since the silicon ion has 4 electrons, thus there is a covalent bond is perforated (holes). Hole is described as an electron acceptor that is ready to accept. Thus, a deficiency of electrons cause the semiconductor is a p-type.

trivalent atom doping 

Resistance

P-type semiconductor or n-type by itself is nothing but a resistor. Just like carbon resistors, semiconductors having resistance. This method is used to create a resistor in a semiconductor component. However a large minor resistance that can be obtained because of limited volume of the semiconductor itself.

PN diode

If the two types of semiconductor material is attached - use glue probably yes:), then the connection will be obtained PN (pn junction) is known as a diode. In the type material of manufacture is P and N type is not connected to harpiah, but from one material (monolithic) to give doping (impurity material) is different. 

p-n connection 

If given a forward voltage (forward bias), where P side voltage is greater than the N, electrons can easily flow from the N side to fill the void of electrons (holes) in the P.

forward bias 

Conversely, if given a reverse voltage (reverse bias), understood that no electrons can flow from the N side of the fill hole on the side of P, because the voltage potential on the N side is higher.
Diode will only be able to stream flow in one direction only, so it is used for applications rectifier circuit (rectifier). Diode, Zener, LED, varactor and varistor are some connections PN semiconductor components are discussed in a special column. 

Bipolar Transistor

The transistor is a diode with two connections (junction). Connections that form the PNP and NPN transistor. The ends of the terminal in a row are called emitter, base and collector. Base is always in the middle, between the emitter and collector. These transistors are called bipolar transistor, because the structure and working principle of the displacement of electrons depends on the negative pole to fill shortage of electrons (holes) in the positive pole. bi = 2 and polar = pole. William Schockley in 1951 who first discovered bipolar transistors.

NPN and PNP transistors 

Will be explained later, the transistor is a component that works as a switch (switch on / off) and also as an amplifier (amplifier). Bipolar transistor is the innovation that replaces the transistor tubes (vacuum tube). In addition to the bipolar transistor dimensions are relatively smaller, power dissipation is also smaller so it can work in colder temperatures. In some applications, transistor tubes are still used primarily in audio applications, to get good sound quality, but power consumption is very large. For to be able to release electrons, the technique used is as in the heating filament incandescent lamp.

DC Bias

Junction bipolar transistor has a second that can be equated with the incorporation of 2 pieces of diodes. Emitter-Base is a base-collector junction and other junctions. As in the diode, current will only flow only if given a positive bias, ie only if the voltage on the material P is more positive than the material N (forward bias). In the following illustration NPN transistor, the base-emitter junction are positively biased while the base-collector gets a negative bias (reverse bias).

Electron current NPN transistor 

Because the base-emitter got it as a positive bias on the diode, electrons flow from emitter to base. Collectors in this series is more positive because it gets a positive voltage. Because the collector is more positive, the flow of electrons moving toward this pole. For example there is no collector, the flow of electrons will be entirely toward the base as in the diode. But because the base width is very thin, only a portion of electrons that can be joined with the existing holes on the base. Most will penetrate the base layer toward the collector. This is why if the two diodes can not be combined into a transistor, because the requirements are that the width of the base must be very thin so it can be hit by electrons.
If for example the base-emitter voltage is reversed (reverse bias), then it will not happen the flow of electrons from the emitter to the collector. If gently 'tap' given base forward bias (forward bias), electrons flow towards the collector and the magnitude of the bias current is proportional to the given base. In other words, adjust the amount of base current of electrons flowing from emitter to collector. This is called the strengthening effect transistors, because of the small base currents produce emitter-collector current is greater. The term amplifier (reinforcement) to be misguided, because with the above explanation is actually occurring is not strengthening, but a smaller flow control a larger current flow. Can also be explained that the base set to open and close the emitter-collector current flow (switch on / off).
In the PNP transistors, the same phenomenon can be explained by giving a bias as shown below. In this case the so-called displacement current is the flow hole.

Hole current PNP transistors
 

To facilitate discussion of the principle of further bias transistor, the transistor parameters of the following is the terminology. In this case the current direction of the potential is greater to a smaller potential.

potential flow

IC: collector current
IB: base flow
IE: the emitter currents
VC: voltage collector
VB: base voltage
VE: emitter voltage
VCC: voltage at the collector
VCE: collector-emitter voltage clamp
VEE: the voltage on the emitter
VBE: base-emitter voltage clamp
ICBO: current base-collector
VCB: collector-base voltage clamp
Please note, although no difference in the doping material for the emitter and collector, but in practice the emitter and collector can not be reversed.

cross section of a bipolar transistor 

From a silicon material (monolithic), the emitter is made first, then base with different doping and the last is the collector. Sometimes also the effect of diodes made on the terminals so that the flow will only occur in the desired direction.

source : patas121.blogspot.com