Where to buy high purity semiconductors?

this could be fun

martin

there was a kit on the market for a diffusion doped solar cell done on a hot plate in air.

Look, most junctions in the beginning were done with oven diffusion in a quartz tube under vacuum, with a induction heater heating the silicon rod. If you first melt a segment of the rod and move the molten zone, the impurities will move with the melt. You can then move impurities into the rod the same way you diffused them out. The trick is picking where to slice the rod on either side of the junction. Buy a doped wafer and apply what you need to the surface, and then cook it on that side. Vacuum metalizing is easy if you sputter, as is chemically applied silver (Brashear process). Bonding would be done with indium onto the metalized pads.

do a google for "midwest tungsten" for evaporation supplies.

Steve

I used to work for a place where one of their products was a molecular beam epitaxy machine. I think it went for about $300,000-$400,000. =:-O

Cheers! Rich

This is not the silicon hot pad diffusion element site, but its a start :

I'd cheat and press the oxide against ITO glass.

Steve Roberts

google the following

"N+ silicon solar cells emitters realized using phosphoric acid as doping source in a spray process "

Steve

Books from the 60s are good IMHO.

Oooohh, and visit your local university's EE library! Tons of old reference works and thesises (theses?) to peruse! On all subjects!

I'm struggling to understand this. Two questions that are stumping me:

Several people have recommended buying a wafer. It was my impression that at the microscopic scale even undoped silicon has relatively low resistance. Perhaps I'm wrong. Anyhow, lets use the simplest semiconductor, a diode. Could someone _please_ tell me how a schottky diode is made on a doped wafer? It appears the recommended method is to somehow etch a long thin _hole_ into the wafer and then deposit metal into the hole to make the metal contact-- imagine shoving a thin metal plate sideways into the doped wafer. Then etch two similar holes on the outside of that and deposit the ohmic contact material, thus forming a schottky diode. Perhaps etching is easier than I thought. Anyhow, that's one simple diode, but how would multiple components work on the same doped wafer then the doped wafer itself has low resistance-- It would short out the entire circuit. I'm guessing that doped wafer would not work, which leads to buying an undoped wafer and using evaporator deposition (by heating the material in a vacuum) to make the doped areas. Both of these methods are different since it makes the junction plates vertical. My initial plan was to make the junction plates horizontal. Etching such thin vertical hole sounds far more difficult than simply depositing the plate materials on top of the surface. Any thoughts and recommendations would help a lot.

My second question is, if a polysilicon undoped wafer is purchased, and a small area (say 3um x 3um) is coated with ohmic contact material, followed by a similar metal contact coating, and followed by a similar silicon coating, all by means of evaporator deposition (by heating the material in a vacuum), then would the deposited silicon be polysilicon or amorphous? The goal is poly or mono crystalline silicon, or better yet GaAs. The thought is that since the wafer is polysilicon, then the metal atoms would convey the crystal structure to the deposited silicon. Perhaps it would help if the evaporator deposition process is slowed down, or perhaps chilling or heating the wafer. Perhaps it would help if the coating depths are thin, on the order of a few dozen nanometers.

Thanks, Anon

I don't think a raw wafer will have oxide on it, unless you count what would occur naturally (very very slow). I think the Schokty diode is a good idea. If you could get a wafer with epi, then sputter Al on it (as I mentioned in my earlier post), you would get an ohmic contact on one side and a Al-Si juction on the other side. Someone you need to insure the sputtered Al doesn't short the two sides together. I guess a HF etch would be a good idea since there could be a microscopic amount of oxide.

[snip] [snip]

I'm sorry. I'm not following most of that. Perhaps we could use the following image as a reference,

The dark gray is the epiwafer. Don't I need to make small doped areas, the green area?

Could I ask what happens if I sputter metal on top of a epiwafer, and then sputter silicon on top of that metal? What I'm getting at, is the sputtered silicon that is on top of the metal is it amorphous or polysilicon?

Thanks for the help, Anon

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I couldn't follow that website. Look at these::

I don't recall the semiconductor flavor (P or N) for a Schokty, but basically you want a heavily doped layer on one side and a lightly doped layer on the other. The metalization on the heavily doped layer will be an ohmic contact. The metalization on the lightly doped layer with be the diode junction.

I'm not really up on my semiconductor physics. Er, not my job. ;-)

OK, I drew a picture of what I'm talking about of making a simple schottky diode. See this page

I would start with an undoped polysilicon silicon wafer. Then sputter ohmic contact. Then sputter metal contact. Then sputter silicon. Then sputter the top layer ohmic contact. The two pins (anode and cathode) are at the edges to be used for the rest of the circuit on the chip.

Could someone please set me straight on if this is the way to go or not?

Thanks, Anon

I'm lost on what you consider an ohmic contact. Basically the only way you contact silicon is via metal on silicon of sufficient doping to get an ohmic contact.

I never made any semi with poly, though there are solar cells using poly. Generally poly is just used for gates and capacitors.

I think what you really want to get is a wafer that is heavily doped on one side and lightly doped on the other. I believe this is possible with an epi wafer. Ah, here is someone's patent that looks right:

I think CCDs would be built on such a wafer.

Most modern ICs are built on such wafers, with the moderately highly doped side (the shiny side) being an epitaxial layer.