Normally, when you design an electronic gadget, you worry about how hot it will get. Automotive-grade components, for example, often have higher allowable temperatures than commercial parts. However, extremely cold environments, such as deep space or the interiors of quantum computers, are also challenging. Researchers at King Abdullah University of Science and Technology believe gallium oxide may be key to operating near absolute zero.
According to [Vishal Khandelwal], one of the researchers, most conventional electronics fail below -173C or 100K. Quantum computers routinely operate at 4K. However, β-Ga2O3 is a wide-bandgap semiconductor that has low current leakage and works at high temperatures up to 500C. However, it also avoids the freeze-out effect that traps electrons in other semiconductor materials.
The team built two devices from the material seeded with a silicon dopant. The first was a FET with a fin-shaped geometry. The second was an inverter. Both operated reliably down to 2K.
Gallium oxide has many interesting properties. For that matter, so does gallium.
So … what goes wrong with conventional semiconductors at low tempertures? Cursory searching didn’t find an explanation, I suppose because I couldn’t figure out the right search query…
freeze-out effect? I too was hoping for some quantum mechanics explanations but the article has only 3 paraghraphs..
There’s a longer one over at tom’s hardware for what it’s worth. https://www.tomshardware.com/tech-industry/scientists-create-electronic-devices-that-function-reliably-at-extreme-temperatures-using-advanced-silicon-doped-beta-gallium-oxide-semiconductor-material
I was curious too, not sure what went wrong with your search but I found this article you might like.
https://www.numberanalytics.com/blog/ultimate-guide-carrier-freeze-out-semiconductor-physics
Sigh, stupidly lost a longer reply, so here we go.
All semiconductors have potential issues at the low end and real limits at the high end. At the high end, when temperatures become too high, the intrinsic (undoped) material releases carriers so much that there’s like, no difference between the doped and undoped regions and obviously now your transistor structures don’t work. This is related to the bandgap of the material, which is why your USB high power bricks now advertise themselves as “GaN” because GaN has a bandgap of like 3.4 eV vs normal silicon’s 1.1 eV. Higher bandgap = higher temperature operation, provided things don’t like, y’know, melt.
At the low end, at a low enough temperature, if the dopants can’t actually release the carriers due to thermal motion, you just… don’t have carriers, and again, the doped regions don’t act any different, and transistors don’t work. Basically: sure, you might’ve stuck an antimony atom there and it’s got an extra valence electron, but the atom’s so cold that that electron’s not going anywhere.
The low end isn’t an absolute issue though, because at some level of doping the dopants don’t need any thermal energy to release carriers (that’s called a ‘degenerate semiconductor’). It also depends on the structure of the transistor as well (since that locally changes the doping, obviously), and so stuff like GaAs and various FET structures operate in the millikelvin range and O(10 K) operation is common. One physics group I know of was confused when I asked them about low temperature chips (because normally when you buy them, they’re only rated to like -65 C minimum) – they just shove them in liquid nitrogen and rarely have problems.
Here they’re actually talking about getting wide/ultrawide band gap (WBG/UWBG) materials working at cryogenic temperatures (ones that potentially will operate at extremely high temperatures too).