We have investigated the scattering mechanisms limiting the low-temperature electron mobility in unintentionally doped In0.75Al0.25As/In0.75Ga0.25As metamorphic quantum wells grown on GaAs (001) substrates. We found that the mobility is limited by background impurity scattering for densities lower than 2.0 x 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 In0.75Ga0.25As well, the alloy disorder scattering can be reduced, yielding mobilities up to 320 000 cm(2)/Vs at a carrier concentration of 3.1 x 10(11) cm(-2). © 2005 Elsevier B.V. All rights reserved.