DIY BJTs. What process most prevents us making transistors?

[brett]

Hi.
Ok, I understand that the base-collector junction in NPN devices has to vacuum up the electrons, so the base can't be too thick, doping has to be just right, etc. 
But the base-emitter junction seems much simpler.  Just a tad more difficult than making a diode (which is dead easy). 

I wonder whether making our own transistors is whithin the capability of the group here.  I've heard of people using two "whiskers" to find adjacent diodes on lumps of lead ore and getting gains of 2 or 3.  Is this a half-truth, or has somebody done this?
cheers

[Sir H C]

One thing is the dopants are pretty scary chemicals.  Look up arsine gas.  Not a pleasant thing.   That and the temperatures involved in diffusing the dopants are quite high.

It can be done, but it is not something that I would recommend.

[R.G.]

Sir HC is dead right. What keeps us from making transistors is:

1. Materials; you need high purity silicon or germanium. That's probably a special order item at your local hardware store.
2. Dopants. Downright scary. Arsine is just the start.
3. Process chemicals. Hydrofluoric acid, anyone?
4. Environment. What class clean room can you maintain? Not to mention that most laboratory glassware is now on the DEA's controlled substances list and you need to prove you won't go cook methamphetamines or worse if they deign to sell you a lab retort or flask.
5. Equipment. Doping ovens run at several hundred to a thousand C. My toaster oven won't get there, even if I do have it in a class 10K clean environment. Photoresist, glass photomasks and shortwave UV lithography is tricky.

None of that is to say that you can't make A transistor. The first germaniums were made by taking a slab of high purity germanium, N-doped, then putting slabs of indium on each side of it and baking this sandwich in a diffusion oven. Works great. The gains, voltage, etc, etc, depend on the doping of the basic germanium slab and the temperature and temp profile of the baking. Once you get it out (and cooled!) you need to establish ohmic connections to base (that's the slab in the middle), emitter and collector.

That can be done with cat's whisker needles, as you note with galena ore crystals, or by plating on metal, then soldering or ultrasonicly bonding gold lead wires. The cat's whisker contacts are somewhat unreliable, but if you want it to work once, they're fine. Old radio amateurs used galena crystal detectors and had brass cups for them that had a setscrew and an adjustable spring loaded cat's whisker for the contact.

On the other hand, there is a market in old, used, surplus semiconductor equipment. You might be able to get great deals on the stuff, but that would be fairly expensive.

[Paul Marossy]

My question is: Why would you want to make your own?! Transistors are cheap these days, why bother with all that nasty stuff when you can typically buy 100 transistors for $10-20 which are pretty consistently manufactured? 

[burnt fingers]

I agree with paul. Si trannys are next to nothing even at Rshack.  Even paying the premium for Smallbears matched Ge's is still more cost effective ( and safer). 

Scott

[Eb7+9]

Like SirHC said, nowadays Silicon wafers are doped at 1100~1300 degC under pressure using Hydrogen gas as a carrier for the doping elements such as Boron which is highly toxic, let alone running hydrogen gas under pressure at those temps ... not a DIY friendly recipe unless you want a Darwin award attached to your name ...

You may want to look into a most amazing "free energy" researcher named Thomas Henry Moray - his transistors preceded Bell lab's by 20 years ... his work "might" lead to a doable approach :

http://www.aethmogen.com/wri/radams/tenigma1/10ent/01txt.shtml
http://en.wikipedia.org/wiki/Thomas_Henry_Moray
http://merlib.org/node/1588

... take XTRA care !!

jc

[phaeton]

My question is: Why would you want to make your own?! Transistors are cheap these days, why bother with all that nasty stuff when you can typically buy 100 transistors for $10-20 which are pretty consistently manufactured? 

Never try to put bounds on the DIY Spirit

Not money.  Not reason.  Not anything.

I agree that he'll have a hard time making any quantity of semiconductors at home.  But hopefully he'll view its manufacturing difficulties as the obstacles, not the "but you can just go buy some for $0.15 apiece" part.  You can buy a decent calculator with scientific functions and everything for about $2.99, but there are some people that will build a 16-bit adder out of bubblegum wrappers, chickenwire, pencil graphite and spit just because they can.

(This is coming from a guy who has built all kinds of crap that was impractical as hell.)

[Paul Marossy]

You can buy a decent calculator with scientific functions and everything for about $2.99, but there are some people that will build a 16-bit adder out of bubblegum wrappers, chickenwire, pencil graphite and spit just because they can.

Not me! There is a place where I draw a line in the sand. If I can buy it for cheaper than I can build it and not have to spend a week building it, I'll just buy one. Most of the things that I have built are things that you can't buy anywhere, and those are the things I'll spend money/time on. I certainly would never try to build a vacuum tube (or insert device here) for anything other than educational purposes - what's the point? And even then, there are more lines in the sand when it comes to practicality and safety.

[phaeton]

You can buy a decent calculator with scientific functions and everything for about $2.99, but there are some people that will build a 16-bit adder out of bubblegum wrappers, chickenwire, pencil graphite and spit just because they can.

Not me! There is a place where I draw a line in the sand. If I can buy it for cheaper than I can build it and not have to spend a week building it, I'll just buy one.

And that's fine!  Everyone's got different things that yank their crank.  My motivations are a tad different- i do things just to do them, i just like to tinker with stuff.  This might explain why I haven't really cloned any commercial pedals, for instance, but I've built a whole smattering of my "own" hodgepodge concoctions which are possibly not very useful to anyone else.  I used to hand-make electric motors some time ago- using solenoids, magnets, 'crankshafts' and 'pistons' and things to make an electrical version of an internal combustion engine.  They were all inefficient, noisy, expensive (comparatively) and didn't last very long.  But an electric V8 or L6 in a radio-controlled Lego car was more cool than a $1.50 rotary (can) motor from Radio Shack....(or so i thought)

And even then, there are more lines in the sand when it comes to practicality and safety.

Well yeah, I should have included that in my post... i assumed that part was 'assumed'.  Never screw around with stuff that's liable to kill you even if you do everything right.  Namely chemicals or explosives or things like that.  High Voltage electrical circuits like tube amps are perfectly safe if you're competent and follow the methods and procedures for safety.  I'm personally not ready to play with tubes, and this is good because I'm not horribly motivated to do so.  I'm still having fun blowing up cheap transistors and diodes up to 18V.

[RaceDriver205]

lol, I'll go out and mine my copper and extract it. And then Ill purify it and extrude it into wires. Then ill make my own fibreglass and coat it with copper. Then ill go and dig up some lead and tin - to make "The 'ultimate DIY' pedal" .
Dont even get me started on making a BBD!
As long as it produces the result, its good for me anyway.