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close this bookRadio and Electronics (DED Philippinen, 66 p.)
close this folder9. ACTIVE COMPONENTS -1- DIODES
close this folder9.2. THE PN-JUNCTION OR DIODE
View the document(introduction...)
View the document9.2.1. PN-JUNCTION CONNECTED TO VOLTAGE
View the document9.2.2. CHARACTERISTICS OF A PN-JUNCTION OR DIODE
View the document9.2.3. ZENERDIODE

(introduction...)

The next step of explanation is a totally theoretical one, because in reality a material with two zones - a N-type and a P-type one - is created in practice by doping with from two opposite sides with two different materials.

But in order to understand the effect, it will be imagined here, that both types are ready prepared and then brought together. As soon as they are near to each other the free chargecarriers near to their border will move in direction to each other as shown in fig. 86 j.


fig. 86j

Of course will the positive and the negative chargecarriers meeting at the border at once cancel each other.


fig. 86k

But the cancellation of chargecarries on each side will leave the opposite chargecarriers belonging to them back. This will lead along the border to a so called SPACE-CHARGE-REGION, which is represented in fig. 86 l (top).


fig. 86l

This space-charges prevent now the free charge carriers from both sides to cross the border and to go on cancelling eachother.

At last there will appear a voltage across this border which is depending on the material used. So the intruding of the chargecarriers from one side to the other is called DIFFUSION this voltage is called DIFFUSION POTENTIAL. In technical sense it will be called THRESHOLD VOLTAGE (Ge = 0.2 V/Si = 0.7 V)

As we derived above, the free chargecarriers around the border cancelled eachother. This leaves on the other hand a zone in which we will find no more free chargecarriers a so called DEPLETION ZONE (Depletion means to get poor). From the point of view of conductivity means this:

THIS ZONE HAS NO CONDUCTIVITY AND AN ALMOST INFINITE RESISTANCE.