  We report the effect of the insertion of an InP/In$_{0.53}$Ga$_{47}$As
Interface on Rashba spin-orbit interaction in
In$_{0.52}$Al$_{0.48}$As/In$_{0.53}$Ga$_{0.47}$As quantum wells. A small spin
split-off energy in InP produces a very intriguing band lineup in the valence
bands in this system. With or without this InP layer above the
In$_{0.53}$Ga$_{47}$As well, the overall values of the spin-orbit coupling
constant $\alpha$ turned out to be enhanced or diminished for samples with the
front- or back-doping position, respectively. These experimental results, using
weak antilocalization analysis, are compared with the results of the
$\mathbf{k\cdot p}$ theory. The actual conditions of the interfaces and
materials should account for the quantitative difference in magnitude between
the measurements and calculations.
