CROSS-SECTIONAL SCANNING-TUNNELING-MICROSCOPY OF EPITAXIAL GAAS STRUCTURES

The scanning tunneling microscope is used to study GaAs epitaxial stru ctures, 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 wid th at pn junctions. In the vicinity of the pn junctions, net donor con centrations of greater than 2 X 10(19) cm-3 are observed. This interfa cial donor activity is an order-of-magnitude higher than that found in the bulk. In the second application, low-temperature-grown and anneal ed GaAs is studied. Arsenic precipitates are observed in the material. The precipitates are found to produce electronic states within the Ga As band gap, and these states cause the Fermi level to be pinned near midgap.