Year: 2020
Type: article
Abstract: Si 24 is a new, open-framework silicon allotrope that is metastable at ambient conditions. Unlike diamond cubic silicon, which is an indirect-gap semiconductor, Si 24 has a quasidirect gap near 1.4 eV, presenting new opportunities for optoelectronic and solar energy conversion devices. Previous studies indicate that Na can diffuse from micron-sized grains of a high-pressure Na 4 Si 24 precursor to create Si 24 powders at ambient conditions. Remarkably, we demonstrate here that Na remains highly mobile within large (~100 µ m) Na 4 Si 24 single crystals. Na readily diffuses out of Na 4 Si 24 crystals under vacuum with gentle heating (10 −4 mbar at 125 °C) and can be further reacted with iodine to produce large Si 24 crystals that are 99.9985 at% silicon, as measured by wavelength-dispersive x-ray spectroscopy. Si 24 crystals display a sharp, direct optical absorption edge at 1.51(1) eV with an absorption coefficient near the band edge that is demonstrably greater than diamond cubic silicon. Temperature-dependent electrical transport measurements confirm the removal of Na from metallic Na 4 Si 24 to render single-crystalline semiconducting samples of Si 24 . These optical and electrical measurements provide insights into key parameters such as the electron donor impurity level from residual Na, reduced electron mass, and electron relaxation time. Effective Na removal on bulk length scales and the high absorption coefficient of single-crystal Si 24 indicate promise for use of this material in bulk and thin film forms with potential applications in optoelectronic technologies.
Institutions: Carnegie Institution for Science, Geophysical Laboratory
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: bronze
Awards: G102163711, G1055550527, G107546177, G1313983767, G1664757510, Discovery and Biological Signatures of Microbiome-Derived Xanthohumol (XN) Metabolites and their Role in Ameliorating Inflammatory Bowel Disease (IBD), G1996433053, G222768804, G2287611682, G262962599, G2702915538, G3075337988, G3589692066, GEO CARS: A NATIONAL RESOURCE FOR EARTH, PLANETARY AND ENVIRONMENTAL SCIENCE RESEARCH AT THE ADVANCED PHOTON SOURCE, Facility Support: GeoSoilEnviroCARS: A National Resource for Earth, Planetary, Soil and Environmental Science Research at the APS, G498139845, G513797252, New forms of silicon with enhanced optoelectronic properties, G6470673664, G6848031779, G6918803902, G7088026799, G7275060768, G969889393, GEO CARS: A NATIONAL RESOURCE FOR EARTH, PLANETARY AND ENVIRONMENTAL SCIENCE RESEARCH AT THE ADVANCED PHOTON SOURCE, G993149817
OpenAlex ID: W3000485367