Experimental Control of the Number of Ionized Donors in an AlGaAs/GaAs Heterostructure

The high mobility of electrons in AlGaAs-GaAs heterostructures relies on the concept of modulation doping. As a sample is cooled down to T = 4.2 K under a fixed gate bias the number of ionized donors can be frozen and is then independent on the gate potential. We discuss the consequences of this procedure on the electron density and mobility in a two-dimensional electron gas. For a laterally patterned sample we find that the amplitude of the potential modulation can be maximized for a given carrier density by a suitably chosen cool-down voltage.