Scattering mechanisms in undoped In0.75Ga0.25As/In0.75Al0.25As Two-Dimensional Electron Gases

We have investigated the scattering mechanisms limiting the low-temperature electron mobility in unintentionally doped In0.75Al 0.25As/In0.75Ga0.25As metamorphic quantum wells grown on GaAs (0 0 1) substrates. We found that the mobility is limited by background impurity scattering for densities lower than 2.0×10 11 cm-2, and by the combination of this mechanism and alloy disorder scattering for higher densities. From such analysis we estimate an alloy disorder scattering potential of about 0.5±0.1 eV. Moreover we show that when a strained InAs layer is located in the centre of the In 0.75Ga0.25As well, the alloy disorder scattering can be reduced, yielding mobilities up to 320 000 cm2/Vs at a carrier concentration of 3.1×1011 cm-2.