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.
We describe an alternative strategy to the fabrication of Ge-Sn based materials on Si by using chlorogermane (GeH3Cl) instead of the specialty Ge hydrides (Ge2H6, Ge3H8, Ge4H10) currently employed as...
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