High mobility GaAs heterostructure field effect transistor for nanofabrication in which dopant-induced disorder is eliminated

We have fabricated field effect transistors with undoped GaAs channels, undoped Al_xGa_1-xAs barriers, and either n⁺GaAs or epitaxial Al gates. Low resistance ohmic contacts are made separately to the gate and channel in samples with 250 Å barriers and in which the depth of the channel below the top surface is 900 Å. Because electrons in the channel are neutralized by conducting charge on the gate, they do not experience the dopant-induced disorder inevitable in modulation doped structures. Electron mobility is above 10⁶cm²/V s, even when their Fermi wavelength exceeds 1000 Å, making these devices ideally suited for nanofabrication.