Synthesis and optical properties of Sn-rich Ge_{1-X -y}Si _xSn_y materials and devices

Sn-rich Ge_{1 - x - y}Si_xSn_y alloys (y > x) have been deposited on Si(100) using recently developed growth processes aimed at achieving the material quality and compositions required to investigate their optical emission properties. The samples are produced using two different methods, each providing optimal quality material within distinct composition ranges of low (2-4% Sn and 1-2% Si) and high (5-10% Sn and 3-4% Si) Sn and Si contents, allowing a comprehensive investigation of their optical response over the targeted 2-10% Sn range. The growth processes are based on ultra-low temperature (310-260 °C) Ultra-High Vacuum Chemical Vapor Deposition and Gas-Source Molecular Beam Epitaxy techniques using stoichiometric reactions of highly reactive hydride sources, including Ge₄H₁₀, Ge ₃H₈, Si₄H₁₀ and SnD₄. Under these conditions the depositions produce monocrystalline layers exhibiting high quality microstructure, flat surfaces, and large thicknesses of 450-600 nm. The latter provide a significantly high volume-fraction of GeSiSn active component away from the inherently defective GeSiSn/Si(100) interface, leading to dramatically improved optical quality materials which are found to exhibit a tunable direct-gap photoluminescence below 1550 nm. Photocurrent measurements of prototype photodiodes were also used to corroborate and further explore the dependence of the direct gap on the Si/Sn concentration. Collectively the results indicate that thermally superior Ge_{1 - x - y}Si _xSn_y alloys may offer an alternative technology to Ge _{1 - y}Sn_y analogs for long-wavelength applications beyond the absorption edge of elemental Ge.