🚀 go-pugleaf

In article <83708@bu.edu>, raju@bass.bu.edu (rajminder Singh) writes:
> Hi there! I am  taking a course in Solid State Physics but I still 
> haven't been able to answer the basic question of why the voltage drop
> in a Silicon p-n junction is around 0.7 Volts ? Does this vary significantly
> with the doping level ? What about the effect of temperature, current and
> the energy band gap (E) of the material used in the junction ?
> 
Well, YES! is the answer to all of the above!  And, if I had my
textbooks with me from 10 years ago, I'd through big, nasty looking
complicated theoretical equations at you untill you couldn't stand
it.  Basically, the diode drop depends heavily upon the energy band
gap of the material(s) used, and that is a quantum level measurement
of the amount of energy it takes to get an electron and/or "hole" 
out of the "base" level into the conduction band.  Now, throw in
all the fun and games you get with imperfections in the crystal
lattice, >>and<< the fact that both the base and conduction bands
are actually many "close together" bands, that the number of
defects in the lattice and the speed of the electrons (not to
mention some fun stuff like tunneling) depend upon temperature and
the equations really get hairy.  However, they do, to a first
order approximation, collapse to the good 'ol standard diode
equation.  And you know how off >>that<< can be in reverse bias,
breakdown, and when you're running any substantial current through
the thing.  (Spice users take note:  When was the last time a
data sheet manufacturer put in the values for >>all<< the
parameters that the Spice model calls for?  And the Spice model
itself is just an approximation!)
	Well, it's early April.  If you're taking a "back to the
basics" course in solid state, they're probably still chugging
along in the details.  I expect you'll hit the diode equation in
the next week or so.  Good luck!


			Ken Becker