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Cadmium Zinc Telluride: The wonder material powering a medical 'revolution'

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53 points 1659447091 | 1 comments | 12 Dec 25 01:41 UTC | HN request time: 0s | source
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analog31 ◴[12 Dec 25 04:04 UTC] No.46240765[source]▶
This isn't much more than a factoid, but notice that many of the useful semiconductors are made from elements that straddle the column containing silicon and germanium. Making compounds whose outer shell electrons add up to be silicon-like lets you make semiconductors, but with electrical and optical properties that you can tune. GaAs is another one, and the LED's are made by choosing particular combinations that have specific bandgap energies corresponding to colors of photons.

Part of the "magic" involves finding ratios of elements that have relatively little mechanical strain, because the atoms "fit" just right, which introduce defects that degrade the semiconductor behavior.

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gsf_emergency_6 ◴[12 Dec 25 07:37 UTC] No.46241776[source]▶
Factoids are facts without citation, I suppose the other factoid to be mentioned is the direct band gap (which CZT has?)

https://en.wikipedia.org/wiki/Direct_and_indirect_band_gaps

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1. adrian_b ◴[12 Dec 25 09:16 UTC] No.46242314[source]▶
For those unfamiliar with this, when a semiconductor has a direct band gap that means that it is likely to be suitable for devices that emit or detect photons, because when photons are absorbed, they generate electron-hole pairs, and when electron-hole pairs combine, their energy is released as photons.

In semiconductors with indirect band gap, when electron-hole pairs combine they usually just heat the material, instead of emitting light, which is why silicon, for instance, is not suitable for making LEDs.

While a direct band gap is desirable in LEDs, lasers and photodetectors, an indirect band gap is preferable in other applications where you do not want electrons and holes to recombine easily, e.g. in bipolar transistors or SCRs and in many kinds of diodes.