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Re: Temperature behaviour of semiconductors

I can tell you roughly what happens to a PN junction as it ages .. the 
P and N majority carriers diffuse, so what starts out as a sharp P-N 
junction gradually becomes less sharp, and very thin regions like 
bipolar transistor bases slowly disappear.  I think MOSFET's are 
somewhat less affected by this because they use field effect to create 
a conductive channel through a more homogeneous substrate, but I know 
the classic NPN and PNP types have a limited lifetime because of this.  
So do SCR's and triacs, etc.  Incidentally, this is why semconductor 
devices typically fail to a short rather than an open circuit.

Where extreme temperatures come into this is that they speed up the 
diffusion, sometimes rapidly, and can cause thin and lightly doped 
regions like bases or SCR/triac gates to diffuse away into the 
surroundings.  High density VLSI chips are also subject to this.  It 
happens to all doped semiconductor eventually, but the thinner the 
features, the faster they fade away, and the hotter the device, the 
faster stuff moves around from thermal motion of the charge carrier 
nuclei ..

On Saturday, Sep 13, 2003, at 14:25 US/Central, William Leijenaar wrote:

> I am still looking for data about the behaviour of electronical 
> components under extreem temp. comditions. I remember that I red some 
> physics book for about 2 years what explained the physical changings 
> of a PN barier with increasing temperature, and also why silicon is 
> used instead of Germanium etc etc... but I can't find it anymore. I 
> can't find any usefull information about this topic at all.
"Oh yeah? Well, I speak LOOOOOOOUD, and I carry a BEEEEEEEger stick -- 
and I use it too!"  **whop!**   -- Yosemite Sam

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