Gating high mobility silicon-germanium heterostructures

Possible methods for fabricating gates to modulate the carrier density of modulation-doped Si/SiGe two-dimensional electron gas (2DEG) material have been investigated. Plasma anodised oxides with Al gates along with Pt/Al Schottky barriers have demonstrated excellent modulation of the 2DEGs. For the plasma oxides, the subsequent low temperature mobility of the material depended on the thickness of oxide grown relative to the consumption of the capping layers of the Si/SiGe material. For an oxide which just consumes the silicon cap, the gates do not adversely affect the as-grown mobility of the material. The application of a bias to the gates of the thicker oxide samples produced similar mobilites as the ungated wafer when the carrier densities were matched.