Cross-sectional scanning tunneling microscopy of epitaxial GaAs structures

Abstract

The scanning tunneling microscope is used to study GaAs epitaxial structures, cleaved in ultrahigh vacuum, and viewed in cross section. Two applications are described: in the first, the net donor concentration in Si-doped GaAs is deduced by direct measurement of the depletion width at pn junctions. In the vicinity of the pn junctions, net donor concentrations of greater than 2×1019 cm−3 are observed. This interfacial donor activity is an order-of-magnitude higher than that found in the bulk. In the second application, low-temperature-grown and annealed GaAs is studied. Arsenic precipitates are observed in the material. The precipitates are found to produce electronic states within the GaAs band gap, and these states cause the Fermi level to be pinned near midgap.