A Schottky diode's junction is some kind of metal to silicon
junction, which conducts differently, with a smaller forward voltage
drop.  (I always get the spelling wrong, you got it right, its
"Schottky" and capitalized, its the inventor's name.  I wonder which
company got THAT patent for a dollar?)

> So if schottkies are so fast, why dont they make transistors out of them?
> or do they?
Schottky diodes are not necessarily all that fast.  The 1N5817,
for example, is a Schottky rectifier, but its rated for use at 60Hz,
which by switching regulator standards is SLOOOW.

And there are diodes that are ultra-fast that are not Schottky
diodes.

However, the diodes used in switching power supplies must be BOTH
very fast and low drop for best efficiency.  The huge quantities
of switchmode power supplies being built has created a huge demand
for fast Schottkys, that makes them common and therefore cheaper.

I think the best way to build a transistor using metal / silicon
junctions is called a MOSFET.  They DO make those :)

Semiconductor Physics was a while ago, so I don't remember if the
Schottky junction trick is applicable to bipolar transistors.
Usually, low forward drop is not an issue in bipolar transistors,
since the controlled current (Collector current) is not flowing
across a regular forward-biased PN junction.

------------
Barry King, KA1NLH
Engineering Manager
NRG Systems "Measuring the Wind's Energy"
Hinesburg, Vermont, USA
barry@nrgsystems.com
"The witty saying has been deleted due to limited EPROM space"