Local electrical transport studies of individual self-assembled quantum dots using ballistic electron emission microscopy

Quantum structures and specifically quantum dots are of great scientific and practical interest, exhibiting the effects of lowered dimensionality including quantum confinement and discretized energy states. Self-assembled quantum dots are of particular interest because they occur as a natural consequence of the growth process, and can be formed with few processing steps. Their small {dollar}rm ({lcub}<{rcub} 500A ){dollar} lateral size however prohibits traditional transport measurements due to the difficulty of forming electrical contacts to single dots. The imaging and spectroscopic capabilities of the scanning probe technique ballistic electron emission microscopy (BEEM) have been exploited to image and locally probe individual self-assembled dots for the first time. Topographical images of the surface above InAs dots in a GaAs matrix show that the capping layer is strongly affected by the presence of the dots, dominating the transport through the dots. Fine structure in BEEM spectra through InAs dots implies the existence of localized zero-dimensional states within these dots. Images and spectra of GaSb dots in a GaAs matrix establish the existence of a staggered band lineup with a local conduction band offset at the dot, and provide a first measurement of this offset.