ATOMIC-SCALE COMPOSITION FLUCTUATIONS IN III-V SEMICONDUCTOR ALLOYS

Composition fluctuations in epitaxially grown III-V compound semicondu ctor alloys are observed with atomic resolution in direct space. A tun neling microscope technique is employed on the (110) cross-sectional p lane of epitaxially grown InGaAsP-InP and AlGaAs-GaAs multilayers clea ved in ultrahigh vacuum. The tunneling polarity is used to image the f illed-state group-V (As,P) sublattice in InGaAsP and the empty-state g roup-III (Al,Ga) sublattice in AlGaAs. In both compounds, the atomic-s cale variations observed in the charge density reflect the composition fluctuations in the respective sublattices: an attempt is made to ide ntify different elements of similar valence (Al,Ga). The definition of the heterojunction interface can be directly assessed on the atomic s cale.