Surface Characteristics of Etched and Non-etched Silicon Germanium (SiGe)/Si Graded Structure with Varying Ge Concentration Grown by Ultra-high Vacuum (UHV)/Chemical Vapor Deposition (CVD) for Optoelectronic and Power Conversion Applications

Report No. ARL-TR-6128
Authors: Fred Semendy, Patrick Taylor, Greg Meissner, and Priyalal Wijewarnasuriya
Date/Pages: September 2012; 24 pages
Abstract: Graded high-quality silicon germanium (SiGe) epitaxial layers were grown on n-type Si with varying Ge concentration using low-temperature ultra-high vacuum (UHV)/chemical vapor deposition (CVD). The graded layers were grown on Si substrates followed by a final growth of doped Si1-xGex with varying percentage of Ge for comparison study. Various techniques, including atomic force microscopy (AFM), optical reflectance, and transmission were used to characterize the surface and structural quality of the materials. The investigation also included for the first time the reflectivity and absorbance of etched black silicon-germanium (Si1-xGex). Black Si1-xGex was produced by metal enhanced chemical etching using nanometer-scale gold particles as the catalyst and hydrogen fluoride (HF):hydrogen peroxide (H2O2):acetic acid (CH3COOH) as the etchant. The etched surface was black and textured, and showed strong suppression of reflectivity and enhanced absorption in the near-infrared, which are consistent with Si1-xGex becoming highly surface-textured due to metal catalysis and wet etching. Lowering reflection and enhancing absorption in Si1-xGex is an important milestone towards practical, extended wavelength (~2 ¼m) electro-optical applications. There is good evidence that varying Ge concentration affects the surface properties across different techniques in determining layer composition and thickness. The surface root-mean-square roughness before etching measured by AFM for all the samples indicate very smooth surfaces.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2012