Semiconductors and how they work...

[Urmi]

Semiconductor Physics...

Hi everyone! I've just got a few questions to ask about semiconductor diodes and what hapens inside them. My questions are:

1.In terms of diode resistance and current,what happens in a diode at extremely large forward biases? (i.e does the intrinsic resistance value of the diode decrease? Also,the current can't really become infinite,so do all the bonds in the semiconductor break up?)

2.How does zener diode regain itself after the breakdown...I mean during breakdown ,all the bonds break up and the diode kind of blasts....but then we can use the same zener diode for later applications,so how do all the broken bonds in the diode restored all on their own?

3. Often,electrons generated as a result of electron-hole pair generation cross the depletion region....how is this possible? Aren't the electrons supposed to be repelled back by the stationary charges in the depletion region?

 

[Urmi]

Anyone? Please please please help!:?:

 

[IanP]

Each diode is rated to carry a certain amount of current, once this level is exceeded, the diode will begin to overheat. Once the diode gets hot enough, the junction can melt. If this happens, the diode can start to conduct on both directions and will be destroyed. Another thing to remember is that even though a diode won't allow current to flow in the opposite direction under normal conditions, it is possible to introduce enough voltage that it jumps across the junction anyway. This will cause damage to the diode and it will not function any more. (The junction may vaporize!)

The above quote describes behavior of all diodes, including Zeners ..
So, if you keep current under control, by for example adding resistor in series, nothing dramatic happens and a diode can function {almost} for ever ..

IanP


quoted from:
**broken link removed**

 

[Urmi]

Hey,thanks IanP!! That short paragraph certainly addressed my first two questions very well.
Could you help me with the last question too,please?

 

[rahul.6sept]

In case of diodes recombination of E-H pairs takes place simultaneously along with generation of free electrons (charge carriers)in case of forward bias.

In case of Zener i'll have to refer book and then reply.

Regards,