Atomic-scale composition fluctuations in III-V semiconductor alloys

Composition fluctuations in epitaxially grown III-V compound semiconductor alloys are observed with atomic resolution in direct space. A tunneling microscope technique is employed on the (110) cross-sectional plane of epitaxially grown InGaAsP-InP and AlGaAs-GaAs multilayers cleaved in ultrahigh vacuum. The tunneling polarity is used to image the filled-state group-V (As,P) sublattice in InGaAsP and the empty-state group-III (Al,Ga) sublattice in AlGaAs. In both compounds, the atomic-scale variations observed in the charge density reflect the composition fluctuations in the respective sublattices: an attempt is made to identify different elements of similar valence (Al,Ga). The definition of the heterojunction interface can be directly assessed on the atomic scale. © 1993 The American Physical Society.