Silicon-germanium interdiffusion in strained Ge/SiGe multiple quantum well structures

A strain-symmetrized Ge/Si0.35Ge0.65 multiple quantum well (MQW) structure has been grown on a relaxed Si0.2Ge0.8 virtual substrate by reduced pressure chemical vapour deposition. The as-grown Ge/Si0.35Ge0.65 MQW structure with one period thickness of 25 nm (14 nm/11 nm) was annealed in nitrogen ambient at different temperatures from 550 to 750 degrees C. The thermal stability and interdiffusion properties were studied by high-resolution x-ray diffraction. No obvious interdiffusion or strain relaxation in the Ge/Si0.35Ge0.65 MQW structure was observed for annealing temperatures <= 600 degrees C, while the onset of interdiffusion occurred as the temperature was increased to above 650 degrees C. The interdiffusion coefficient was obtained by analysing the decay rate of Ge/SiGe periodic satellites in the recorded intensity at temperatures 650-750 degrees C. The extracted activation energy was found to be 3.08 +/- 0.1 eV for the strained Ge/Si0.35Ge0.65 MQW structure with an average Ge composition of 85 at%.