Extended Compositional Range for the Synthesis of SWIR and LWIR Ge 1– y Sn y Alloys and Device Structures via CVD of SnH 4 and Ge 3 H 8

A chemical vapor deposition (CVD) strategy is presented for the synthesis of Ge 1– y Sn y alloys on Si wafers with band gaps in the short-wave infrared (SWIR) range of 1.8–2.6 μm, as well as in the long-wave infrared (LWIR) at 12 μm and beyond. This broad compositional versatility is achieved by CVD reactions of Ge 3 H 8 and SnH 4 as Ge and Sn precursors, respectively. The use of conventional SnH 4 instead of the previously used SnD 4 is found to be critical in synthesizing alloys with Sn contents between 30 and 36%, suggesting that at very low temperatures required to grow these supersaturated alloys, the incorporation of Sn is reaction-rate-dependent. The SnD 4 precursor was historically preferred to SnH 4 due to its longer lifetime at room temperature. However, the difference is found not to be significant from a practical perspective, and the fact that SnH 4 can be synthesized from cheap and readily available starting materials represents a significant cost reduction and portends feasibility for commercial applications. The subtle differences between SnD 4 and SnH 4 that may explain why alloys with Sn incorporation higher than 30% can only be achieved with the latter are discussed in detail. Optical experiments indicate that such concentrations may be sufficient to cover much of the LWIR range. Device structures containing SWIR Ge 1– y Sn y alloys were grown with the SnH 4 precursor to demonstrate its suitability as a viable Sn source. The fabricated heterostructure pin diodes display excellent structural properties and a clear rectifying behavior, providing evidence that SnH 4 is a practical and versatile CVD source of Sn at all concentrations of practical interest.