Extended Compositional Range for the Synthesis of SWIR and LWIR Ge_1–ySn_y Alloys and Device Structures via CVD of SnH₄ and Ge₃H₈

Abstract

A chemical vapor deposition (CVD) strategy is presented for the synthesis of Ge1–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 Ge3H8 and SnH4 as Ge and Sn precursors, respectively. The use of conventional SnH4 instead of the previously used SnD4 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 SnD4 precursor was historically preferred to SnH4 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 SnH4 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 SnD4 and SnH4 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 Ge1–y Sn y alloys were grown with the SnH4 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 SnH4 is a practical and versatile CVD source of Sn at all concentrations of practical interest.

Synthesis of High Sn Content Ge1–x–ySixSny (0.1 < y < 0.22) Semiconductors on Si for MWIR Direct Band Gap Applications

“…Extrapolating to a fully strained film with 20% Sn, the strain would reach a value of −2.7%, which is unrealistic and would likely result in a catastrophic relaxation that renders the sample unsuitable for optical applications. This phenomenology is analogous to that observed in the case of Ge 1– y Sn y /Ge, where the high strain is the limiting factor for the incorporation of ever higher Sn fractions . The solution in that case was to forego the Ge buffer and grow directly on Si, and we adopt a similar strategy here.…”

Molecular Sn(ii) precursors for room temperature deposition of crystalline elemental tin

“…Our solution-based routes to Sn metal provides alternatives to known gas/vapor phase methods, such as the use of SnH 4 in the formation of tin-containing materials by chemical vapor deposition. 2,9…”

Transfer-printing-enabled GeSn flexible resonant-cavity-enhanced photodetectors with strain-amplified mid-infrared optical responses

“…Recent theoretical studies have reported that the performance of GeSn PDs is comparable, and can be even superior to that of the current commercially available semiconductor MIR PDs, 24,25 which make it a promising candidate for low-cost practical applications. Despite the limited solubility of Sn in Ge of ∼1%, 27,28 the recent advancements in low-temperature growth techniques using molecular beam epitaxy (MBE), 27,28 chemical vapor deposition (CVD), [29][30][31] and sputter 32 have enabled the growth of high-quality GeSn layers on Si or silicon-on-insulator (SOI) substrates, which can yield Sn contents up to 36%. 30 Various GeSn-based PDs have been demonstrated with an extended photodetection range, [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] attaining up to 3.7 µm 47 and enhanced quantum efficiency, which highlights their potential for efficient MIR photodetection.…”

“…Despite the limited solubility of Sn in Ge of ∼1%, 27,28 the recent advancements in low-temperature growth techniques using molecular beam epitaxy (MBE), 27,28 chemical vapor deposition (CVD), [29][30][31] and sputter 32 have enabled the growth of high-quality GeSn layers on Si or silicon-on-insulator (SOI) substrates, which can yield Sn contents up to 36%. 30 Various GeSn-based PDs have been demonstrated with an extended photodetection range, [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] attaining up to 3.7 µm 47 and enhanced quantum efficiency, which highlights their potential for efficient MIR photodetection. However, the epitaxy of GeSn layers on Si or SOI substrates typically requires an appropriate buffer (usually Ge) to improve the material quality and induces an indispensable biaxial compressive strain.…”