Comment by Daniel204

I would like to clarify your second point. The "2D Hole Gas" is not a thin layer of voids in the diamond. It is rather an absence of electrons in that layer. Holes are a pseudo particle with positive charge and a different mass from electrons (effective mass). All semiconductors have them when you excite electrons, but they're generally not used as the main charge carriers, as their mass tends to be larger than electrons, making them less mobile