  We report on transport characteristics of field effect two-dimensional
electron gases (2DEG) in 24 nm wide indium arsenide surface quantum wells. High
quality single-subband magnetotransport with clear quantized integer quantum
Hall plateaus are observed to filling factor $\nu=2$ in magnetic fields of up
to B = 18 T, at electron densities up to 8$\times 10^{11}$ /cm$^2$. Peak
mobility is 11,000 cm$^2$/Vs at 2$\times 10^{12}$ /cm$^2$. Large Rashba
spin-orbit coefficients up to 124 meV$\cdot$\r{A} are obtained through weak
anti-localization (WAL) measurements. Proximitized superconductivity is
demonstrated in Nb-based superconductor-normal-superconductor (SNS) junctions,
yielding 78$-$99% interface transparencies from superconducting contacts
fabricated ex-situ (post-growth), using two commonly-used experimental
techniques for measuring transparencies. These transparencies are on a par with
those reported for epitaxially-grown superconductors. These SNS junctions show
characteristic voltages $I_c R_{\text{N}}$ up to 870 $\mu$V and critical
current densities up to 9.6 $\mu$A/$\mu$m, among the largest values reported
for Nb-InAs SNS devices.
