Role of Al_xGa_1-xAs buffer layer in heterogeneous integration of GaAs/Ge

The material and optical properties of the GaAs/Al_xGa _1-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 Al_xGa_1-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 Al_xGa _1-xAs buffer layer suggests that the compressive strain at the Al_xGa_1-xAs-GaAs interface is compensated by the tensile strain at the Ge-Al_xGa_1-xAs interface when x ∼ 0.3. Al_xGa_1-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.