Self-limiting segregation and incorporation during boron doping of Si and SiGe

We have studied the experimental conditions to obtain highly boron-doped thin layers (delta-doping) in Si and SiGe during gas source molecular beam epitaxy (GSMBE). Pre-deposition and the co-deposition of boron have been compared by secondary ion mass spectroscopy (SIMS) and electrochemical capacitance-voltage profiling eC(V). We have shown that provided a pre-deposition step is used before co-deposition, higher doping levels are obtained without degrading the abruptness of the interfaces. This is explained by a coverage limit of boron during the pre-deposition step, above which islanding occurs and degrades the crystalline quality of the film. In addition, a reflection high-energy electron diffraction (RHEED) oscillation study shows that there exists a virtually constant boron coverage of the surface during the Si and SiGe overgrowth, which produces a decrease of the growth rate.