Gallium Arsenide. Semiconductor with certain nicer properties than silicon that allow it to switch faster and have a larger operating temperature at the cost be

Gallium Arsenide. Semiconductor with certain nicer properties than silicon that allow it to switch faster and have a larger operating temperature at the cost being harder and more expensive to manufacture. That's a fairly big caveat, being a lot of the reason why silicon is so ubiquitous, relegating adoption of other semiconductors to more niche applications where their more optimal properties are a necessity.