Characterization of reduced pressure chemical vapor deposited Si _0.8Ge_0.2/Si multi-layers

We have investigated the Si_0.8Ge_0.2/Si multi-layer grown directly onto the Si (001) substrates using reduced pressure chemical vapor deposition. The thicknesses of the Si_0.8Ge_0.2/Si multi-layer were determined using transmission electron microscopy. From the results of energy-dispersive X-ray spectroscopy and X-ray diffraction analyses on the Si_0.8Ge_0.2/Si multi-layer, Ge composition in the Si_1-xGe_x layers was determined as ∼20% and the value of residual strain ε of the Si_0.8Ge_0.2 layer is calculated to be 0.012. Three peaks are observed in Raman spectrum, which are located at approximately 514, 404, and 303 cm^-1, corresponding to the vibration of Si-Si, Si-Ge, and Ge-Ge phonons, respectively. The photoluminescence spectrum originates from the radiative recombinations both from the Si substrate and the Si_0.8Ge_0.2/Si multi-layer. For the Si_0.8Ge_0.2/Si multi-layer, the transition peaks related to the quantum well region observed in the photocurrent spectrum were preliminarily assigned to e-hh and e-lh fundamental excitonic transitions.