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Growth of tin-free germanium carbon alloys using carbon tetrabromide (CBr4)

https://doi.org/10.1063/5.0172330

Reza, Md Shamim; Dey, Tuhin; Arbogast, Augustus W; Muhowski, Aaron J; Holtz, Mark W; Stephenson, Chad A; Bank, Seth R; Wasserman, Daniel; Wistey, Mark A (November 2023, Journal of Applied Physics)

Direct bandgap group IV materials could provide intimate integration of lasers, amplifiers, and compact modulators within complementary metal–oxide–semiconductor for smaller, active silicon photonics. Dilute germanium carbides (GeC) with ∼1 at. % C offer a direct bandgap and strong optical emission, but energetic carbon sources such as plasmas and e-beam evaporation produce defective materials. In this work, we used CBr4 as a low-damage source of carbon in molecular beam epitaxy of tin-free GeC, with smooth surfaces and narrow x-ray diffraction peaks. Raman spectroscopy showed substitutional incorporation of C and no detectable sp2 bonding from amorphous or graphitic carbon, even without surfactants. Photoluminescence shows strong emission compared with Ge.
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Gas Source Techniques for Molecular Beam Epitaxy of Highly Mismatched Ge Alloys

https://doi.org/10.3390/cryst6120159

Stephenson, Chad; Gillett-Kunnath, Miriam; O’Brien, William; Kudrawiec, Robert; Wistey, Mark (December 2016, Crystals)

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Extended Defect Propagation in Highly Tensile-Strained Ge Waveguides

https://doi.org/10.3390/cryst7060157

Qi, Meng; O’Brien, William; Stephenson, Chad; Patel, Victor; Cao, Ning; Thibeault, Brian; Schowalter, Marco; Rosenauer, Andreas; Protasenko, Vladimir; Xing, Huili; et al (June 2017, Crystals)

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Band structure of germanium carbides for direct bandgap photonics

https://doi.org/10.1109/PHOSST.2016.7548543

Stephenson, Chad A.; O'Brien, William A.; Gillett-Kunnath, Miriam; Yu, Kin Man; Kudrawiec, Robert; Stillwell, Roy A.; Wistey, Mark A. (July 2016, Photonics Society Summer Topical Meeting Series (SUM), 2016 IEEE)

Ab-initio simulations of dilute germanium carbides (Ge:C) using hybrid functionals predict a direct bandgap with <;1%C. Growth of dilute Ge:C shows reduced direct gap consistent with the model, with no structural defects detected. Ge:C may enable lasers and compact modulators on Si.
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