We have studied molecular beam epitaxy growth and magneto-transport of novel In
xGa
1−xAs/In
xAl
1−xAs (
x=0.5 and 0.75) inverted modulation-doped heterojunctions. Large Rashba-type spin–orbit coupling constants,
20×10
−12 eV m, as well as high two-dimensional electron mobilities,
μe2×10
5 cm
2/V s, have been confirmed at
1.5 K. It was also found that larger
’s were confirmed in the higher In-content heterojunctions with thinner InGaAs surface channel. These results are qualitatively explained by the differences in the energy bandgap, the electron effective mass, and the mean electric field strength at the heterojunction interface. The above features of
and
μe, seem to be promising in the applications in the spintronic devices as well as in the mesoscopic structures for novel spin physics based on the Rashba spin–orbit interaction.