ATOMIC-SCALE ANALYSIS OF QUANTUM NANOSTRUCTURES WITH THE STM

Important features of semiconductor quantum structures can be observed by cross-sectional scanning tunneling microscopy down to the atomic s cale. The MBE-grown III-V multilayers are cleaved in UHV to expose an atomically flat cross-sectional plane, which is then imaged with the S TM. Chemically selective imaging enables us to distinguish between ato ms within the group III and analyze the AlGaAs composition in atomic d etail: we find Al clustering on the scale of a few nanometers in many MBE-grown materials. The heterojunction interfaces and their roughness can be analyzed down to the unit-cell lattice period. The electronic signature of active dopants such as Be is observed and quantified. Rec ent work shows that all these possibilities can be used to study the M BE growth of AlAs/GaAs superlattices on V-grooved substrates with unpr ecedented detail.