COMPARATIVE-STUDY OF CROSS-SECTIONAL SCANNING-TUNNELING-MICROSCOPY SPECTROSCOPY ON III-V HETEROSTRUCTURES AND HOMOSTRUCTURES - ULTRAHIGH VACUUM-CLEAVED VERSUS SULFIDE PASSIVATED

A comparative study of surfaces prepared by sulfide passivation and by UHV cleaving using cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S) is performed. Test samples used include both GaA s/(AlGa)As heterojunctions and GaAs pn junctions. Sulfide-passivated h eterojunction surfaces allow much useful electronic information to be deduced from the tunneling spectroscopy since the tip-induced band ben ding problem is solved. Atomic resolution across UHV-cleaved heterojun ctions allows a direct measurement of the asymmetrical interfacial rou ghness which agrees very well with the value deduced from tunneling sp ectroscopy on the sulfide-passivated surface. In the case of the UHV-c leaved p n junction surface, the tip-induced band bending effect is se en to manifest itself as a spatial shift in the conductivity profile w ithin the depletion region. Sulfide-passivated pn junctions show a top ographic profile which correlates very well with the secondary ion mas s spectrometry profile, indicating that this technique is a potentiall y powerful dopant profiling method. Each type of prepared surface poss esses its own advantages and disadvantages which are discussed. In par ticular, we address the manifestation of the tip-induced band bending effect in the tunneling spectroscopy.