How does a semiconductor work?

Answer 1

we know that in a transistor we have three types of regions: EMITTER, COLLECTOR, BASE, and we know that emitter is highly doped, so charge carriers are very high, so resistance is very less, and on the other side collector is moderately doped so charge carriers are less, so resistance is very high. So from the above concept we conclude that in a transistor current is flowing from low resistance to high resistance. for example the 100 electrons are moving from emitter to base, in base only some (4 electrons) of the electrons are neutralized, and remaining 96 electrons are moved to collector terminal through high resistance path. so now same current flowing through high resistance so voltage amplified.

Answer 2

There are two kinds of transistor: Bipolar Junction Transistors (BJTs) and Field Effect Transistors (FETs). These two transistors work in two different ways. However, both types of transistors are based on the fact that when a voltage is applied to impure semiconductor such as Silicon, it changes from a conductor to an insulator or vice versa.

Field Effect Transistors contain a narrow conductive channel which passes near a "Gate" electrode. The two ends of this channel are connected to terminals called "Source" and "Drain." When a voltage of the correct polarity is applied between the Gate and the transistor channel, the channel becomes wider, and if this polarity is reversed, the conductive channel narrows, or it even vanishes entirely. By changing the size of this conductive channel, the FET behaves as a voltage-controlled valve or switch. Since the Gate does not require any continuing current, the FET operation can be improved by including a layer of insulating glass (Silicon oxide) between the gate electrode and the rest of the transistor. This type of FET is called a "MOSFET," for Metal-Oxide-Semiconductor layers. Transistors without the glass layer are called JFETs or "Junction-FETs."

Bipolar transistors are composed of three segments called "Collector," "Base," and "Emitter." A thin insulating layer arises naturally between Base and Emitter. If a voltage of the correct polarity is applied to the Base and Emitter terminals, the insulating layer becomes so thin that it behaves as a conductor. If this voltage polarity is reversed, the insulating layer becomes wide. By changing the thickness of this insulating layer, the BJT behaves as a voltage-controlled valve or switch. HOWEVER, whenever the Base-Emitter voltage is causing the insulator layer to become thinner, there also is a leakage current in the base terminal. This tiny current is proportional to any larger current passing through the entire transistor. Although the BJT is controlled by the voltage between Base and Emitter, designers usually ignore the base-emitter voltage, and the BJT is treated as a current-controlled valve or switch.

All transistors are made of a "doped" semiconductor, typically silicon. Pure silicon contains almost no movable charges, so it behaves as an insulator. To create transistors, the silicon crystal has impurities deliberately introduced during manufacture. Each impurity atom will "donate" a movable charged particle in the silicon, which changes the silicon into a conductor. Doped silicon is very different than metal conductors. The charges within metals behave like a dense liquid, while the charges in doped silicon behave as a highly compressible gas. Doped semiconductor is a special kind of conductor where an externally-applied voltage can easily "compress" or sweep the charges away. By sweeping the charges away, the semiconductor is changed from a conductor back into an insulator. Semiconductors are like electric switches or valves, but with no moving parts.

Answer 3

== == A semiconductor is created primarily by silicon. Silicon is a substance that has four electrons in its outer electron shell, making it very suitable for creating crystals. When you introduce an "impure" substance, such as boron or gallium in small doses, it causes the crystal to become unstable. This instability can be either positive (an impurity with less than 4 electrons in its outer shell) or negative (an impurity with more than four electrons in its outer shell). The imbalance of electrons now allows current to flow through the silicon in restricted amounts, thus the term SEMIconductor. It is not as restrictive as an insulator and not as free-flowing as a conductor.

Answer 4

controls current going into a load There are two kinds of transistor: Bipolar Junction Transistors (BJTs) and Field Effect Transistors (FETs). These two transistors work differently. However, both are based on the fact that whenever a voltage is applied across impure semiconductor such as Silicon, the Silicon changes from a conductor to an insulator or vice-versa.

FETs

Field Effect Transistors contain a narrow conductive channel which passes near a "Gate" electrode. The two ends of this channel are connected to terminals called "Source" and "Drain." When a voltage of the correct polarity is applied between the Gate and the transistor channel, the channel becomes wider, and if this polarity is reversed, the conductive channel narrows, or it even vanishes entirely. By changing the size of this conductive channel, the FET behaves as a voltage-controlled valve or switch. Since the Gate does not require any continuing current, the FET operation can be improved by including a layer of insulating glass (Silicon oxide) between the gate electrode and the rest of the transistor. This type of FET is called a "MOSFET," for Metal-Oxide-Semiconductor layers. Transistors without the glass layer are called JFETs or "Junction-FETs."

BJTs

Main Circuit (+)

` ` ` ` ` |

` ______|_______

` | ` ` ` ` ` ` ` `'|

` | COLLECTOR N |

` |_____________|

` | ` ` ` ` ` ` ` `| ` ` ` ` ----->

` | ' BASE P ` ` `|______________

` |_____________| ` ` ` ` ` ` ` ` `| +

` | ` ` ` ` ` ` ` ` | ` ` ` ` ` ` ____|____

` | ` EMITTER N ` | ` ` ` ` ` ` ` _____

` |_____________| ` ` ` ` ` ` _________ "Base Battery"

` ` ` ` ` | ` ` ` ` ` ` ` ` ` ` ` ` _____

` ` ` ` ` |______________________| -

` ` ` ` ` |

` ` ` ` ` |

` ` ` Main Circuit (-)

In between each semiconductor segment is a "depletion layer", which acts as a sort of variable insulator, or variable resistor. The higher the voltage across the "depletion layer" the less insulated it becomes. The Base/Emitter Voltage across the "depletion layer" is controlled by the voltage source (your base battery) or the battery connecting your "base" and "emitter" semiconductor sections. The voltage across this depletion layer opens the floodgates across the entire transistor from a separate voltage source. The base voltage proportionally controls the transistor voltage so in other words it could be said that: "controls current going into a load". In other words, it sort of acts like an on off switch which can be partially opened.

• FETs are voltage controlled variable resistors, as are vacuum tubes
• BJTs are current controlled current amplifiers

The transistor is like an electronic switch. It can turn a current on and off. A simple way you can think of it is to look at the transistor as a relay without any moving parts. A transistor is similar to a relay in the sense that you can use it to turn something ON and OFF.

The transistor works because of something called a semiconducting material. A current flowing from the base to the emitter "opens" the flow of current from the collector to the emitter.

In a standard NPN transistor, you need to apply a voltage of about 0.7V between the base and the emitter to get the current flowing from base to emitter. When you apply 0.7V from base to emitter you will turn the transistor ON and allow a current to flow from collector to emitter.

Answer 5

The Related Link to Answers.com's site, shown below this answer, gives a good description of a photo-transistor.

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Answer 6

Transistor operates as a switch by providing minute forward bias voltage or no voltage between base emitter junction.

If forward bias is zero volts; transistor collector current becomes zero or collector impedance becomes infinite. By applying minute forward bias voltage at base emitter junction, collector current flows in terms of amps. This is how transistor works as a switch.

Answer 7

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