Heterojunction band lineups in Si-Ge alloys using spatially resolved electron-energy-loss spectroscopy

We describe a new method for determining band lineups at semiconductor heterojunctions, applicable to Si-Ge systems. Spatially resolved transmission electron-energy-loss spectroscopy is used to detect bulk core-to-conduction-band transitions in alloys. The core levels then provide relatively accurate ‘‘reference levels’’ for aligning bands across an interface. This approach eliminates the major sources of experimental uncertainty in other methods, while permitting the study of local regions within more complex structures (e.g., real devices). Valence-band offsets in Si-Ge systems are found to vary linearly with Ge content, reaching 0.78 eV (strain-averaged) for interfaces between pure Ge and Si.