  Although most theoretical calculations of quantum wells with non-square
profiles assume that material composition is varied continuously, it is more
common in experiment to grow digital alloys. We compare the Rashba spin-orbit
interaction of triangular wells using continuous, discrete, and digital
alloying profiles in (001)-grown triangular InSb/Al_f(z)In_(1-f(z))Sb, finding
a very large difference between digital alloying and the others, including a
sign change in the Rashba spin-orbit coupling. We find that the interface
contribution to the Rashba spin-orbit coupling is much larger in the
continuously- and discretely-alloyed triangular quantum wells than in the
digitally-alloyed triangular wells, in which it is almost completely absent.
The electric field contribution, however, is quite similar in all three
systems. Due to a much stronger doping dependence in all three systems, the
electric field contribution dominates at higher dopings, although the very
large offset due to the near absence of interface contribution in
digitally-alloyed wells persists.
