Photoluminescence and transmission electron microscopy investigation of SiGe quantum wires grown on patterned Si substrates

Growth of SiGe by low pressure chemical vapor deposition on nonplanar Si substrates is studied for nominal Ge concentrations of 0.4 less than or equal to x(Ge)(nom.) less than or equal to 1. Self-organized growth leads to the formation of approx, 30 nm wide SiGe quantum wires at convex corners of the substrate. In photoluminescence (PL) spectra of samples with x(Ge)(nom.) = 0.4 we identify transitions from quantum wells on the flat parts of the substrate and from quantum wires. The energetic positions of the quantum wire transitions are in good agreement with Ge concentrations measured by spatially resolved energy dispersive X-ray spectroscopy, using a scanning transmission electron microscope (TEM), We find that the Ge concentration inside the wire is considerably lower than the nominal value for growth on planar parts of the substrate. Even for wires grown with x(Ge)(nom.) = 1, where only GeH4 and H-2 are present during growth, PL and TEM indicate a Ge concentration as low as 32% for the wires. In such growth experiments we observe different regimes of strain relaxation. While quantum wires and wells are heavily decorated with Stranski-Krastanov islands in larger structures, smaller structures (less than or equal to 5 mu m) exhibit homogeneous thickness.