Direct experimental measurements were made of a new mechanism for Fermi-level pinning in Si-doped (001) GaAs. Scanning tunnelling microscopic imaging showed that high levels of Si doping caused the (100) 2 x 4 unit cells to re-order, via the formation of kinks in the dimer vacancy rows. It was shown that these kinks were surface acceptors which formed in numbers that were precisely those required in order to compensate the surface region. It was found that, in the depleted layer, all of the incorporated Si atoms were donors at Si concentrations of up to at least 1019/cm3.

M.D.Pashley, K.W.Haberern: Physical Review Letters, 1991, 67[19], 2697-700