Control of Ge-Homojunction Band Offsets Via Ultrathin Ga-As Dipole Layers

Band offsets of 0.35-0.45 eV are produced at Ge homojunctions by placing a monolayer of As and an adjacent monolayer of Ga between the two Ge bulks. The "Ga-first" and "As-first" growth sequences exhibit band offsets of similar magnitude but opposite sign, consistent with a truly dipolar effect. To our knowledge, this is the first time that intralayer control of band discontinuities is extended to homojunctions, thereby expanding the potential domain of band offset engineering. The offsets were measured with photoemission spectroscopy. The existence, sign, and approximate magnitude of the effect are correctly predicted by a "theoretical alchemy" model.