Self-limiting Sb monolayer as a diffusion source for Ge doping

A new method for the creation of high-quality, fully electrically active junctions to be applied in nanostructured semiconductor materials is explored in this work. The method consists in a gas phase antimony deposition on Ge, which gives rise to an antimony self-limiting behavior to form a monolayer (ML) on the Ge (100) surface. The ML formation is characterized by a wide thermal process window in terms of time and temperature. Synchrotron radiation Angle Resolved X-ray Photoelectron Spectroscopy shows that the ML structure consists in oxidized Sb grown over a very thin layer of Ge oxide, and a small amount of metallic Sb is embedded beneath the Ge surface during the deposition process. Interestingly, during the ML formation process native Ge oxide is reduced without the need of strong acid pre-treatments. By performing further thermal annealing in equilibrium conditions, Sb diffusion can be faithfully described by a well assessed diffusion model. Finally, processing the Sb monolayer with Pulsed Laser Melting technique, which is a strongly out-equilibrium diffusion process, allows to exploit the entire Sb ML as a dopant source, thus achieving junctions with a very high dopant concentration (1.2 × 1020 cm-3 Sb surface concentration) and a 100% Sb electrical activation.