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 GaAs/(AlGa)As heterojunctions and GaAs pn junctions. Sulfide-passivated heterojunction surfaces allow much useful electronic information to be deduced from the tunneling spectroscopy since the tip-induced band bending problem is solved. Atomic resolution across UHV-cleaved heterojunctions allows a direct measurement of the asymmetrical interfacial roughness which agrees very well with the value deduced from tunneling spectroscopy on the sulfide-passivated surface. In the case of the UHV-cleaved p n junction surface, the tip-induced band bending effect is seen to manifest itself as a spatial shift in the conductivity profile within the depletion region. Sulfide-passivated pn junctions show a topographic profile which correlates very well with the secondary ion mass spectrometry profile, indicating that this technique is a potentially powerful dopant profiling method. Each type of prepared surface possesses its own advantages and disadvantages which are discussed. In particular, we address the manifestation of the tip-induced band bending effect in the tunneling spectroscopy.