Ge-rich homogenous GeSi alloying induced by Si–Ge interdiffusion under high temperature thermal cyclic annealing

Thermal cyclic annealing (TCA) is recognized as the key process in improving Ge film quality during epitaxial growth on Si substrates. In Ge-on-Si systems, annealing temperatures rarely exceed 900°C due to the limitation of the Ge melting point (938°C). In this study, ultra-high temperature TCA is performed on a series of 500 nm Ge buffer layers grown on Si (001), with the upper limit ranging from 900 to 950°C. The structural properties of the Ge thin films are investigated, indicating that an optimized TCA profile occurs with the upper annealing temperature just below the melting point of Ge. Higher annealing temperature above the melting temperature of Ge results in homogeneous alloying of Ge and Si, induced by enhanced Si diffusion into Ge. This process produces a Ge_0.75Si_0.25 layer with a threading dislocation density of 3.5 × 10⁸ cm^-2 and a surface roughness of 3 nm. These findings inspire a novel approach for creating Ge-rich GeSi layers on Si, which potentially benefits the Ge/GeSi/Si (001) heterostructures and their applications in advanced Si-based semiconductor devices.