A Comprehensive Study of Growth Techniques & Characterization of Epitaxial Ge_1−xC_x (111) Layers Grown Directly on Si (111) for MOS Applications

Abstract

We report the growth and characterization of thin germanium-carbon layers grown directly on Si (111) by ultra high-vacuum chemical vapor deposition. The thickness of the films studied is 8-20 nm. The incorporation of small amount (less than 0.5%) of carbon facilitates 2D growth of high quality Ge crystals grown directly on Si (111) without the need of a buffer layer. The Ge_1−xC_x layers were grown in ultra high vacuum chemical vapor deposition chamber, at a typical pressure of 50 mTorr and at a growth temperature of 440 °C. CH₃GeH₃ and GeH₄ gases were used as the precursors for the epitaxial growth. The Ge_1−xC_x films were characterized by atomic force microscopy (AFM), secondary ion mass spectroscopy, x-ray diffraction, cross-sectional transmission electron microscopy and Raman spectroscopy. The AFM rms roughness of Ge_1−xC_x grown directly on Si (111) is only 0.34 nm, which is by far the lowest rms roughness of Ge films grown directly on Si (111). The dependence of growth rate and rms roughness of the films on temperature, C incorporation and deposition pressure was studied. In Ge, (111) surface orientation has the highest electron mobility; however, compressive strain in Ge degrades electron mobility. The technique of C incorporation leads to a low defect density Ge layer on Si (111), well above the critical thickness. Hence high quality crystalline layer of Ge directly on Si (111) can be achieved without compressive strain. The fabricated MOS capacitors exhibit well-behaved electrical characteristics. Thus demonstrate the feasibility of Ge_1−xC_x layers on Si (111) for future high-carrier-mobility MOS devices that take advantage of high electron mobility in Ge (111).