BACKGROUND IMPURITY PROFILES DETERMINED BY TUNNELING SPECTROSCOPY

Tunneling spectroscopy is used to determine the background impurity di stribution in the GaAs buffer layer on GaAs-AlGaAs heterostructures. O n a coupled two-dimensional system, consisting of an accumulation laye r and an inversion layer separated by a thin AlGaAs barrier, resonant tunneling processes are used to determine the subband energies and the potential profiles in both two-dimensional channels. Comparing the me asured peak positions in the resonant tunneling current with the resul ts obtained from self-consistent calculations, the depth dependence of the residual charged impurities in the GaAs buffer is obtained over t he first 1200 angstrom below the AlGaAs-GaAs interface. This informati on is a crucial sample parameter for all high-mobility two-dimensional electron systems and cannot be obtained from Hall measurements.