Molecular synthesis of high-performance near-IR photodetectors with independently tunable structural and optical properties based on Si-Ge-Sn.

This Article describes the development of an optimized chemistry-based synthesis method, supported by a purpose-built reactor technology, to produce the next generation of Ge(1-x-y)Si(x)Sn(y) materials on conventional Si(100) and Ge(100) platforms at gas-source molecular epitaxy conditions. Technologically relevant alloy compositions (1-5% Sn, 4-20% Si) are grown at ultralow temperatures (330-290 °C) using highly reactive tetragermane (Ge(4)H(10)), tetrasilane (Si(4)H(10)), and stannane (SnD(4)) hydride precursors, allowing the simultaneous increase of Si and Sn content (at a fixed Si/Sn ratio near 4) for the purpose of tuning the bandgap while maintaining lattice-matching to Ge. First principles thermochemistry studies were used to explain stability and reactivity differences between the Si/Ge hydride sources in terms of a complex interplay among the isomeric species, and provide guidance for optimizing process conditions. Collectively, this approach leads to unprecedented control over the substitutional incorporation of Sn into Si-Ge and yields materials with superior quality suitable for transitioning to the device arena. We demonstrate that both intrinsic and doped Ge(1-x-y)Si(x)Sn(y) layers can now be routinely produced with defect-free microstructure and viable thickness, allowing the fabrication of high-performance photodetectors on Ge(100). Highlights of these new devices include precisely adjustable absorption edges between 0.87 and 1.03 eV, low ideality factors close to unity, and state-of-the-art dark current densities for Ge-based materials. Our unequivocal realization of the "molecules to device" concept implies that GeSiSn alloys represent technologically viable semiconductors that now merit inclusion in the class of ubiquitous Si, Ge, and SiGe group IV systems.