From: andyh@syma.sussex.ac.uk (Andy Holyer)
Subject: Re: TP research
Organization: University of Sussex
Date: Wed, 23 Dec 1992 12:31:54 GMT

In article <1992Dec22.202252.8076@novell.com> rpratt@novell.com (Robert Pratt) writes:
>In article <Bzo62p.Iov@apollo.hp.com> johnf@apollo.hp.com (John Francis) writes:
>>In article <memo.825134@cix.compulink.co.uk> tpratchett@cix.compulink.co.uk writes:
>>>This is a question for all you godless scientists out there:
>>>
>>>What is the troll equivalent of a drug?
>>>What is the troll equivalent of alcohol?
>
>>Bearing in mind the fact that addition of these elements to silicon is
>>refered to as 'doping', I think we have found the troll equivalent of a drug.
>>so we have the following rules for trolls:
>>    1)  Stay away from matches
>>    2)  Don't cook in Aluminium vessels.
>>John Francis                                 johnf@apollo.hp.com
>>with 9 cats to feed, I don't have time to think up a clever .sig
>
>  It seems to me that the natural extension of this is that trolls smoke
>aluminum joints :-), or maybe eat aluminum 'shrooms that human types might
>want to use for lawn decorations.

There's more to it than that: Virtually any element which is reasonably
reactive and which will bond with silicon will do for doping a chip: Metals
(i.e. anything on the LHS of the periodic table are quite common 'cos most of
them are cheap, you get a big bang for the buck, and you don't need to heat
the silicon too much for the dope to stick (this is what MOS IC's are: Metal
Oxide Silicon) There are two types of doping: P-type ans N-type (he says,
frintcally trying to remember details from the first two lectures of a course
he got a "D" in ten years ago :-)

N-type produce spare electrons floating around in the substrate (hence
"Negative". I *think* this is what aluminium, iron etc. produce. P type are
cuter: they make the subtrate have "holes" (as they're called) - i.e. places
where an electron should by rights be, but isn't.

The semiconductor effect occurs at the boundary between two differently-doped
regions. MOS chips have a junction between N-type and vanilla silicon (almost
always). The trendier CMOS (Complementary MOS)uses junctions between P-doped
and N-doped silicon (thus MOS voltages go between minus omega and earth,
whereas CMOS voltages are between -omega/2 and +omega/2. This explains why MOS
chips take more power, and why CMOS chips tend to go foom from the static
charge in your hand :-)

So how do you bugger a semiconductor? Overdope the substrate - or dope it with
the wrong stuff. So we have trolls taking either "uppers" or "downers", and if
they take too much of the wrong one they keel over.  This also raises the
vision of there being N-type and P-type trolls (with a few stick-in-the-mud
germanium adherants, and of course all the trendy gallium arsenide boys
wearing luminous bermuda shorts and blowing whistles at each other :-)

Hope this helps.

&.
-- 
&ndy Holyer, School of Cognitive and     |Due to recent events in the USA,
Computing Studies, University of Sussex, |I find I can no longer use this
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                                         |be resumed when I find another one.
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