  Low-temperature Hall measurements have been performed on two-dimensional
electron gases (2DEGs) induced by deposition of Cs or Na on in situ cleaved
surfaces of p-type InAs. The surface donor level, at which the Fermi energy of
the 2DEG is pinned, is calculated from the observed saturation surface electron
density using a surface potential determined self-consistently. The results are
compared to those of previous photoelectron spectroscopy measurements.
