Semiconductors

Semicondutors

David A. Dietzler, 2007

It has been suggested that regolith be treated with fluorine, hydrofluoric acid or chlorine to make vapors of SiF4 or SiCl4 (b.p. 57.6 at 1 atm) that would then be decomposed on hot tungsten or tantalum filaments at about 800 C. to get rather pure silicon for solar panels. These could be zone refined further for ultra high purity. This would require the upport of large masses of fluorine, HF, or chlorine and these are very corrosive and dangerous chemicals that will attack most materials, except for Teflon. Moreover, very little fluorine or chlorine exists on the Moon. Leakage is always a reality and even recycled reagents become contaminated after many cycles of reuse. Losses might be replenished by halogens boiled off of large masses of volcanic glass that contain zinc, gallium and chlorine on the surfaces of the glass beads, but this would require mining extradordinary tonnages of glass and this stuff won't be nearly as valuable as helium 3, so mining millions of tons of volcanic glass for thousands of tons of chlorine for making millions of tons of solar panels won't be justified.

For solar panel quality silicon we only need to take silicon from magma electrolysis and zone refine it, since it will probably contain some iron and traces of manganese, chromium and sodium. After ten passes in the zone refiner it's purity should be excellent for solar panels. On the Moon we can zone refine much larger bars of silicon than we can on Earth because of the low gravity. The heavier bars won't fall apart at the molten zone as easily. We won't need inert gas filled chambers because we have free vacuum. In space, at the construction shack, we might refine bars of silicon the size of telephone poles because there will be no limit in weightlessness. Perhaps this will be one of the first jobs tackeld at the C-shack, purifiying silicon ingots launched from the Moon to make huge solar panels to increase the shack's power generating capacity.

Though zone refining can produce ultra-high purity silicon, silicon that has been extracted from minerals with halogens to get SiF4 or SiCl4, decomposed with heat, and then zone refined will be even more pure simply because the silicon we start the zone refining with is more pure to begin with. I don't think solar panel construction justifies upporting huge masses of halogens or even salts that will be decomposed later to get halogens, but semiconductor chip making could because chips require the purest silicon and the masses of halogens needed to make them will not be too large.

While computers will be upported from Earth in the early years of lunar and space industrialization, eventually it will make economic sense to make them on the Moon. At today's rates, about $15,000 a pound to the Moon, shipping computers and other electronic devices will be costly. At a third of today's rates, $5,000 a pound, it would cost $40,000 to ship an eight pound $700 notebook computer to the Moon! Eventually, especially as the population in space expands and tourism grows, it will make sense to build computers and other electronics in space. This will require the purest silicon. So the work of scientists who have described methods of treating regolith with halogens to make SiF4 or SiCl4 that is then decomposed with heat has not been in vain. We will need semiconductors labs on the Moon and in orbital space. Not just to make CPUs but also flat panel screens instead of old fashioned CRTs and other parts. We will need to upport dopants, but the mass of these will not be prohibitive. Metal cases and chassis can be made of lunar metals. Keyboards might be made of metal instead of plastic like old fashioned typewriters.

If we are going to spend a trillion dollars to industrialize the Moon and outer space, it doesn't seem ridiculous to me to make a billion of it devices needed to set up semiconductor chip labs and computer shops. Meanwhile, what if somebody breaks his glasses? We could use optical shops too that make eyewear out of in situ materials, because a two ounce pair of lightweight glasses would cost nearly $700 to upport! And glasses cost about $100 or less, depending on where you buy them. Will we also have small pharmaceutical labs too where technicians can whip up just about any drug with chemicals derived from volatiles we mine on the Moon? In case someone looses his pills?

With large masses of purified silicon, could we make large power transistors and diodes for induction heater oscillators??? Large crystals could be grown in the low G of the Moon and the ultra-clean vacuum.