Direct Nanoscale Mapping of the Conduction Band in Semiconductor Heterostructures by Off-Axis Electron Holography

Understanding the spatial variation of the conduction band in semiconductor materials is essential for unraveling charge transport phenomena, especially at interfaces, defects, and in nanoscale devices. However, direct experimental access to the conduction band with the required energy and spatial resolution has remained a major challenge. Here we demonstrate that off-axis electron holography enables direct measurements of the conduction band edge in semiconductor systems with nm-scale spatial resolution. We are able to map conduction band profiles across semiconductor heterostructures, revealing band bending, band offsets, and interface dipoles with unprecedented clarity. This method provides access to the local electronic landscape in real space, without relying on indirect modeling or assumptions about doping profiles. Applied to an InP/In_0.53Ga_0.47As high-speed double heterojunction bipolar transistor for the next generation of telecommunications, our approach uncovers previously inaccessible details of band alignment, opening new avenues for exploring the electronic structure in functional nanostructures.