We present a new etch chemistry that enables highly selective dry etching of germanium over its alloy with tin (Ge(1-x)Sn(x)). We address the challenges in synthesis of high-quality, defect-free Ge(1-x)Sn(x) thin films by using Ge virtual substrates as a template for Ge(1-x)Sn(x) epitaxy. The etch process is applied to selectively remove the stress-inducing Ge virtual substrate and achieve strain-free, direct band gap Ge0.92Sn0.08. The semiconductor processing technology presented in this work provides a robust method for fabrication of innovative Ge(1-x)Sn(x) nanostructures whose realization can prove to be challenging, if not impossible, otherwise.

We theoretically study and experimentally demonstrate a pseudomorphic Ge/Ge0.92Sn0.08/Ge quantum-well microdisk resonator on Ge/Si (001) as a route toward a compact GeSn-based laser on silicon. The structure theoretically exhibits many electronic and optical advantages in laser design, and microdisk resonators using these structures can be precisely fabricated away from highly defective regions in the Ge buffer using a novel etch-stop process. Photoluminescence measurements on 2.7 μm diameter microdisks reveal sharp whispering-gallery-mode resonances (Q > 340) with strong luminescence.

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In-situ phosphorus doped silicon epitaxial film with 2.8 X 10 21 cm -3 doping level is found to show high tensile stress comparable to carbon doped silicon with 1.8% substitutional carbon. As-grown samples show electrically activated dopant concentration of less than 2 X 10 20 cm -3 . The high tensile and low activation could be well explained by formation of a pseudocubic Si 3 P 4 structure in silicon lattice. Film resistivity of 0.29 mOhm-cm could be obtained with 0.25 ms annealing at 1200°C, with slight reduction in tensile strain. Also, 0.23 mOhm-cm could be obtained by millisecond anneal at 1300°C, but with 30% reduction in tensile strain.

An in-situ heavily phosphorous doped selective epitaxial Si:P process was developed to reduce the source/drain contact resistance in the scaled-down 2D and 3D nMOSFET devices. The phosphorous concentration in as-deposited Si:P epitaxial films is >1×10 21 at/cc. Most of phosphorous atoms contribute to the in-film tensile strain that is comparable to Si:CP epitaxial film (with >1 at% C sub ) for nMOSFETs. High-resolution XRD data and cross sectional TEM images demonstrated high quality epitaxial Si:P film grown on differently orientated substrates and planar/fin structures. Furthermore, phosphorous atoms in Si:P films can be highly activated, resulting in a low resistivity of ~0.3 mOhm-cm, by the milli-second anneal treatment without the loss of phosphorous concentration and tensile strain.