The material and optical properties of the GaAs/AlxGa1−xAs/Ge structures grown by metalorganic chemical vapor deposition were examined and found to be dependent of the Al content x. SIMS and PL measurements show that the 10 nm AlxGa1−xAs buffer layer with x = 0.3 and 0.6 are equally effective in suppressing the outdiffusion of Ge, whereas x = 1.0 gives the most abrupt interface. The best morphology with surface rms of 0.3 nm is obtained in the structure with x = 0.3 buffer layer. Analysis on change of strain in the AlxGa1−xAs buffer layer suggests that the compressive strain at the AlxGa1−xAs-GaAs interface is compensated by the tensile strain at the Ge-AlxGa1−xAs interface when x ∼ 0.3. AlxGa1−xAs lattice matched to Ge is crucial for better result in surface morphology, but higher Al content is preferred for eliminating the interdiffusion of atoms at the heterointerface.