Synthesis and materials properties of sn/p-doped ge on si(100): Photoluminescence and prototype devices

We report the fabrication of a new class of Sn/P-doped Ge-like materials with high quality optical, structural, and device properties. A flux of Ge ₂H₆ with trace amounts of SnD₄ is used to deposit thick Sn-doped Ge films via chemical vapor deposition (CVD) at low temperatures (∼390-370 °C) directly on Si(100) substrates. The presence of Sn in the gas mixture alters the standard Ge growth mechanism (Stranski-Krastanov) to yield atomically smooth layers with minimal threading defects at growth rates as high as 15-30 nm/min. The films, dubbed "quasi-Ge", contain ∼10¹⁹ cm^-3 Sn "impurities", which do not produce any measurable shift in the lattice constant or emission wavelength. This new method represents a low-cost, high-performance alternative to the standard CVD approaches to grow high-quality Ge-on-Si for optoelectronic applications. In this regard, the optical quality of the materials is corroborated by studying photoluminescence (PL) of both intrinsic samples and n-type analogues doped well above 10¹⁹ atoms cm^-3, using the single-source P(GeH₃)₃. Heavy n-doping significantly enhances the PL intensity, allowing the observation of distinct indirect and direct gap peaks. The device quality of the material was evaluated by fabricating prototype heterostructure photodetectors in n-i-p geometry. These are found to exhibit significantly higher responsivities than pure Ge p-i-n analogues and dark current densities comparable to the state of the art.