Nanodot Formation in Thermally Annealed UHV-RTCVD Grown Si₁-_XGe_X Epitaxial Layers on Silicon for Photovoltaics

Abstract

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 2 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 submicronpyramidal features at the surface of Si 1-x Ge x 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.