Hex-SiGe: A new direct bandgap semiconductor
Jonathan Finley, TU Munich, Germany
Silicon has dominated the semiconductor electronics industry for more than half a century but the cubic (diamond) forms of Si, Ge and SiGe alloys are all indirect gap materials that do not efficiently emit light. Despite decades of research and innovation, achieving efficient light emission from group-IV materials on silicon technology has remained elusive. However, the hexagonal (lonsdaleite) crystal phase of silicon germanium (Si1-xGex, x>0.6) alloys were recently predicted to be direct band gap semiconductors with tunable bandgaps spanning the technologically relevant infrared spectral range (λ_gap∼1.8 – 3.5 μm)1–3. I will present recent results in which we have developed new approaches for the growth of high-quality hex-Si1-xGex alloys, confirmed that they are indeed direct gap materials with excellent radiative efficiencies and bandgaps in good accord with theory4, understood their composition dependent radiative dynamics and obtained first evidence for optically pumped lasing. We measure sub-nanosecond, temperature-insensitive radiative recombination lifetimes and observe an emission yield similar to that of direct-bandgap group-III–V semiconductors. Experimental findings are in excellent quantitative agreement with ab initio theory.
Supported by the EU via 735008-SiLAS and Opto-Silicon 964191
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3. Rödl, C. et al. Accurate electronic and optical properties of hexagonal germanium for optoelectronic applications. Phys Rev Mater 3, 034602 (2019).
4. Fadaly, E. M. T. et al. Direct-bandgap emission from hexagonal Ge and SiGe alloys. Nature 580, 205–209 (2020).