In Situ Biasing of Tapered Si-Ge NW Heterojunctions using Off-Axis Electron Holography

Heterojunction Si-Ge nanowires (NWs) have potential applications such as field effect transistors [1]. Knowledge of the active dopant concentration and distribution, and resultant built-in potential across the Si-Ge p-n junction under biasing conditions is important for improving device performance. Off-axis electron holography is an effective method to measure electrostatic potential with nanoscale resolution [2,3]. By reconstructing phase images from interference holograms, the projected potential distribution of the sample along the electron beam direction can be quantitatively mapped. Here, we have used off-axis electron holography to measure the potential profile across p-n heterojunctions in Si-Ge NWs in situ under varying biasing conditions. The heterojunction Si-Ge NWs are grown using the vapor-liquid-solid method with AuGa catalyst [4], and consist of a B-doped (~10 18 cm -3 ) tapered Ge base and an untapered P-doped (~10 19 cm -3 ) Si tip.