Abstract
Mobilities and sheet carrier densities of single interface, modulation-doped AlGaAs-GaAs heterostructures depend on the structure and molecular beam epitaxial growth parameters. Variation of the thickness of the undoped spacer between 20 and 360 Å gave electron densities in the range 1012–2×1011 cm−2 in two-dimensional electron gases. Thick spacers resulted in high 4.2-K mobilities of 1.2×106 cm2/Vs in dark and 1.8×106 cm2/Vs under illumination with corresponding channel densities of 2.3×1011 cm−2 and 3.9×1011 cm−2, respectively. Two-dimensional hole gases had mobilities of 83 000 cm2/Vs and hole concentrations of 2.7×1011 cm−2 at 4.2 K.