Impact of doping on epitaxial Ge thin film quality and Si-Ge interdiffusion

Ge-on-Si structures with three different dopants (P, As and B) and those without intentional doping were grown, annealed and characterized by several different materials characterization methods. All samples have a smooth surface (roughness < 1.5 nm), and the Ge films are almost entirely relaxed. B doped Ge films have threading dislocations above 1 × 108 cm−2, while P and As doping can reduce the threading dislocation density to be less than 106 cm−2 without annealing. The interdiffusion of Si and Ge of different films have been investigated experimentally and theoretically. A quantitative model of Si-Ge interdiffusion under extrinsic conditions across the full xGe range was established including the dislocation-mediated diffusion. The Kirkendall effect has been observed. The results are of technical significance for the structure, doping, and process design of Ge-on-Si based devices, especially for photonic applications.