It took me too long to find this: information:

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

From the article - possible replacements for CMOS include:

Rapid single flux quantum devices Carbon nanotube field-effect transistor Silicon nanowire FET Spintronics, various types Tunnel junction devices, e.g. Tunnel field-effect transistor Indium antimonide transistors Photonics, optical computing Graphene nanoribbons Molecular electronics