  We present molecular beam epitaxial grown single- and double-side
$\delta$-doped InAlSb/InSb quantum wells with varying distances down to 50 nm
to the surface on GaSb metamorphic buffers. We analyze the surface morphology
as well as the impact of the crystalline quality on the electron transport.
Comparing growth on GaSb and GaAs substrates indicates that the structural
integrity of our InSb quantum wells is solely determined by the growth
conditions at the GaSb/InAlSb transition and the InAlSb barrier growth. The
two-dimensional electron gas samples show high mobilities of up to 349 000
cm$^2$/Vs at cryogenic temperatures and 58 000 cm$^2$/Vs at room temperature.
With the calculated Dingle ratio and a transport lifetime model, ionized
impurities predominantly remote from the quantum well are identified as the
dominant source of scattering events. The analysis of the well pronounced
Shubnikov$-$de Haas oscillations reveals a high spin-orbit coupling with an
effective $g$-factor of $-38.4$ in our samples. Along with the smooth surfaces
and long mean free paths demonstrated, our InSb quantum wells are increasingly
competitive for nanoscale implementations of Majorana mode devices.
