Solid-state interdiffusion mechanism in strained Si_1-xGe_x/Si heterostructures

The interdiffusion in a low-strained Si_0.93Ge_0.07/Si epilayer was analyzed by double-crystal X-ray diffraction. The interdiffusion was characterized by a low diffusion barrier of 1.81 eV with a diffusion constant of 4.3 × 10^-5 cm²/sec, which indicates correlation with the stacking fault generated by the homoepitaxial growth of the Si layer prior to the growth of the strained SiGe layer. At the very low-strained layer, the driving force causing the interdiffusion is the concentration gradient, and the mechanism is self-diffusion of Si. Furthermore, the interdiffusion mechanisms were classified into three groups, depending on the Ge mole fraction x. For x < 0.2, the diffusion process in the SiGe alloy is similar to a self-diffusion of Si atoms, while, for 0.2 < x < 0.4, Ge atoms prefer to be diffused out from the alloy. Finally, for x > 0.4, Si atoms can be diffused into the alloy.