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Semiconductor devices (I) PN junction
2022-07-05 08:01:00 【Drink more hot water-】
( One ) Intrinsic semiconductor Impurity semiconductor
Intrinsic semiconductor It is a semiconductor with pure crystal structure . The impurities 、 Have a stable structure .
At a certain temperature, the carrier concentration in the intrinsic semiconductor is certain , And the concentration of free electrons and holes is equal .
Impurity semiconductor There are two kinds of :N Type semiconductor P Type semiconductor
N Type semiconductor :
Intrinsic semiconductor doping 5 After the valence element , Some silicon atoms in the original crystal will be replaced by impurity atoms . The outermost layer of impurity atoms has 5 A valence electron , among 4 A covalent bond with silicon , More than one electron is attracted only by its own nucleus , It can become a free electron at room temperature .
Electrons are called majority carriers ( abbreviation children ),Negitive
Holes are called minority carriers ( abbreviation Young son ).
5 Valence impurity atoms are called Donor atom .
P Type semiconductor
In silicon or germanium crystal doped with a small amount of 3 Valence impurity element , Like boron 、 gallium 、 Indium, etc , Composition P Type semiconductor .The hole is ** Most carriers **,Positive Electron is ** Minority carriers ** 3 Valence impurity atoms are called ** Acceptor atom **.
explain :
1. The concentration of doped impurities determines the concentration of most carriers ; Temperature determines the concentration of minority carriers .
2. The number of carriers in impurity semiconductors is much higher than that of intrinsic semiconductors , Therefore, its conductivity is greatly improved .
3. Impurity semiconductors generally remain electrically neutral .
( Two ) PN The formation of knots
PN junction Formation process : Spread 、 Drift movement
Doping on one side of a semiconductor single crystal becomes P Type semiconductor , The other side is doped into N Type semiconductor , A special thin layer is formed at the junction of the two areas , be called PN junction .
original P Area and N All areas are electrically neutral , because children The spread of , It will inevitably lead to the destruction of the electrical neutrality inside the semiconductor , Thus in the conductor PN An internal electric field is formed at the junction : Pay attention to the direction of the internal electric field
The width of the depletion layer is determined by the intensity of the diffusion movement . The resistivity of the depletion layer is very high , It is high resistance area . This is because the resistance reflects the conductivity , The depletion layer has reached dynamic equilibrium , Basically non-conductive , Natural resistance is very large .
Although whether it is diffusion motion or drift motion , The actual motion is all electrons . But in order to distinguish between diffusion motion and drift motion , Diffusion motion is often referred to as multiparticle motion , Because diffusion is the process of many children in this region entering the other region ; The corresponding drift motion becomes the minority carrier motion .
( 3、 ... and )PN The nature of the knot
3.1 Unidirectional conductivity
stay PN Add a small forward voltage to the junction , You can get a larger forward current , To prevent excessive current , Resistance can be connected R.
Reverse current is also called reverse saturation current I S. Very sensitive to temperature , As the temperature rises , IS Will increase dramatically .
3.2 PN The capacitance effect of the junction
When PN When the voltage on the changes ,PN The amount of charge stored in the junction will change accordingly , send PN The junction has a capacitive effect .
Capacitance effect includes two parts : Barrier capacitance 、 Diffusion capacitance
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