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Teaching silicon to lase


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#1 gribbon

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Posted 26 March 2007 - 06:17 AM

Making silicon lasers

Scientists did, some while back, persuade silicon to emit laser beams. Hopefully, computers and other electronics, which currently use low cost silicon chips to transfer information around, will handle light as well as electrons.

C1ay had an article on this, but it doesn’t seem to go into much detail, so I’ll see if I can find out any more here. I will explain as succinctly as possible what was found.

I have always been interested in this particular development, and it is my understanding that scientists had problems with teaching this material to lase, as it has several irksome properties accompanying its usefulness. We do have much more expensive materials which we can use to lase as well, such as Gallium Arsenide, but the obvious aim here was to make things a lot cheaper by using this abundant material. It cannot emit light efficiently when energised, (the first requirement) and what light it does produce is incapable of amplifying into a laser beam by “stimulating” it to create more electrons. (Laser stands for “Light Amplification by Stimulated Emission of Radiation.) It is my understanding that in a laser an external energy source, usually light or an electric current provides the energy to pump the electrons to a higher energy level, and so when these atoms return to their normal/ground state the energy is liberated as a photon. When a photon is absorbed, an electron jumps to a higher level, and when a photon is released, an electron drops to a lower level. If a material has an appropriate crystal lattice, these photons can be amplified when they collide with excited phonons, (which are vibrations occurring in the crystal lattice). The trouble with Silicon is that there is never enough energy to get an electron to jump energy bands just as the result of a photon strike. Usually the electrons lose their energy as heat before a suitable phonon arrives, which prevents the Silicon from producing a constant stream of electrons. It is my understanding that to teach Silicon to lase required scientists to make a quantum cage for the electrons, which would confine their movement to a few directions. As the quantum cage for the electron shrinks, it vibrates quicker and becomes more agitated as the result of the Heisenburg uncertainty principle. A thin film of silicon dioxide glass embedded with pieces of crystalline silicon did the trick, and as these were nano-crystals, only a few atoms wide, they could be pumped and so achieve quantum confinement.

That’s as much as I can remember, and I can’t find the article anywhere on the web or at home, but does anyone know anymore about this? In particular, how do earth metals such as erbium compare in cost to silicon and practicality? I can’t imagine that production of such intricate pieces of silicon can be cost effective. It’s cheaper than Gallium Arsenide, sure, but how much cheaper? Any figures?