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 2 H 6 with trace amounts of SnD 4 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 ∼10 19 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 10 19 atoms cm –3, using the single-source P(GeH 3 ) 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.