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 tha n or equal to x(Ge)(nom.) less than or equal to 1. Self-organized grow th 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 we lls on the flat parts of the substrate and from quantum wires. The ene rgetic positions of the quantum wire transitions are in good agreement with Ge concentrations measured by spatially resolved energy dispersi ve X-ray spectroscopy, using a scanning transmission electron microsco pe (TEM), We find that the Ge concentration inside the wire is conside rably lower than the nominal value for growth on planar parts of the s ubstrate. Even for wires grown with x(Ge)(nom.) = 1, where only GeH4 a nd H-2 are present during growth, PL and TEM indicate a Ge concentrati on 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 struct ures, smaller structures (less than or equal to 5 mu m) exhibit homoge neous thickness.