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 In 0.75 Al 0.25 As/In 0.75 Ga 0.25 As 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 0.75 Ga 0.25 As well, the alloy disorder scattering can be reduced, yielding mobilities up to 320 000 cm 2 /Vs at a carrier concentration of 3.1×10 11 cm −2 .