Next generation of Ge _1-ySn _y (y = 0.01-0.09) alloys grown on Si(100) via Ge ₃H ₈ and SnD ₄: Reaction kinetics and tunable emission

Film growth and reaction kinetics studies have shown that trigermane (Ge ₃H ₈) is a superior Ge source for the epitaxial synthesis of Ge _1-ySn _y/Si(100) alloys using ultra-high vacuum chemical vapor deposition. The Ge ₃H ₈/SnD ₄ combination yields 3-4 times higher growth rates than the traditional Ge ₂H ₆/SnD ₄ approach, with film Sn/Ge ratios reflecting the corresponding gas-phase stoichiometries much more closely. These advances have led to optical quality Ge _1-ySn _y layers with Sn concentrations up to at least 9 and thicknesses approaching 1 μm. These thick films are found to be crucial for the observation of a strong, tunable photoluminescence signal near the threshold of the predicted direct-indirect bandgap crossover.