High mobility GaAs-Al_x Ga_1-x as single period modulation-doped heterojunctions

Single period modulation-doped structures composed of an Al_xGa_1-xAs layer, part of which is doped with Si, on top of an undoped GaAs layer have been grown by molecular beam epitaxy. The films were characterised using Hall effect measurements carried out at temperatures between 10 and 300 K. With 50-75 A thick undoped (Al, Ga)As layers near the interface, mobilities in excess of 115000 cm²/Vs at 10 K and 7450 cm²/Vs at 300 K have been achieved for an average doping concentration of ~ 5 × 10¹⁶ cm^-3. These are some of the highest mobilities as yet obtained from modulation-doped structures, and represent an increase in mobility over equivalently doped GaAs by about a factor of 20 at 10 K and by a factor of 2 at 300 K.