Si₂₄: a next-generation semiconductor with growing promise for future solar energy

The recently discovered allotrope of silicon, Si₂₄, is an exciting material for the future of solar energy due to a quasi-direct bandgap near 1.3 eV [1]. Synthesized via precursor Na₄Si₂₄ at high temperature and pressure (~850 °C, 9 GPa), free standing single crystals of on the 1 mm scale are now achievable [2]. An epitaxial relationship between Na₄Si₂₄ and diamond cubic silicon (DC-Si), observed through high-resolution transmission electron microscopy (HRTEM), is proposed to facilitate the growth of these high-quality Na₄Si₂₄ crystals from DC-Si wafers mixed with metallic Na. These observations illuminate a path toward scaling of Na₄Si₂₄ and Si₂₄. Removal of Na from Na₄Si₂₄ on this length scale is shown to be effective, revealing intrinsic optical and electronic properties of Si_24. Our results encourage the pursuit of Si₂₄ for future solar energy conversion and efficient optoelectronics.
[1] D. Y. Kim, et al., Nat. Mater., vol. 14, no. 2, pp. 169–173, Feb. 2015.
[2] Guerette, M.; Ward, M.; Lokshin, K.; Wong, A.; Zhang, H.; Stefanoski, S.; Kurakevych, O.; LeGodec, Y.; Juhl, S.; Alem, N.; et al. Synthesis and Properties of Single-Crystalline Na₄Si₂₄. Crystal Growth & Design 2018.