Nanodot Formation in Thermally Annealed UHV-RTCVD Grown Si_(1-x)Ge_x Epitaxial Layers on Silicon for Photovoltaics

摘要

The surface and interface of SiGe layers on Si were found to incur drastic changes during layer rapid growth and post-growth rapid annealing. As deposited and thermal annealed samples were characterized using Energy dispersive X-ray Analysis (EDX) enhanced by Monte Carlo simulation for precise evaluation of Ge concentration. X-ray Diffraction (XRD) data exhibited a small shift of the SiGe (400) peak towards low 20 values, which was attributed, primarily, to change in the Ge concentration. Confocal Raman Spectroscopy of samples showed regions of high and low strain that resulted from fluctuations in Ge concentrations. Nano- and submicron-pyramidal features at the surface of Si_(1-x)Ge_s layers (x=17% and 28%) were revealed by Atomic Force Microscopy (AFM) and SEM. Additionally, pyramidal nanodots were revealed for [Ge]=17% samples and high density nanostructure for 28% appeared along the Crosshatch strain pattern induced by misfit dislocations, when annealed at 700°C and 900°C, respectively. The observed Ge-rich nano-features, which were obtained with low thermal budget low cost techniques, are expected to be useful for bandgap engineering and third generation solar cells.