  In this Letter, four-point magnetotransport of high mobility InGaAs/InP
heterointerfaces is measured from 1.6 K to 300 K and from 0 to 15 T, and an
analysis is shown whereby the mobility and density of the two-dimensional (2D)
accumulation layer can be separately characterized from that of the parallel
conducting dopant layer over all but a small intermediate temperature range.
Standard magnetotransport regimes are defined as the temperature increases from
1.6 K to 300 K, namely quantum Hall (QH), Shubnikov de Haas (SdH), and Drude
regimes (D), and in the QH and D regimes different analyses are applied to
deduce densities and mobilities of both layers separately. Quantitative
conditions for the intermediate SdH regime are defined, within which both QH
and D analyses fail. The density and activation energy of unintentional donors
at the InP epilayer/substrate interface is deduced. At base temperature, QH
minima are resolved down to B = 0.4 T at nu = 20, revealing a mobility of mu =
160,000 cm^2/Vs. The 2D system maintains this high mobility up to at least 40 K
in this high quality structure.

Mesoscale and Nanoscale Physics;Materials Science