Bandgap and impedance barriers overcome by shear-synthesized metastable silicon and its implications for effective optoelectronics

ABSTRACT This work effectively synthesized gram-scale nanosilicon with a dual-phase metastable structure (ambient-pressure phase (diamond cubic phase, DC-Si) and high-pressure phase (body-centered cubic phase, BC8-Si)) at room temperature using the dynamic high-pressure shearing technique. In order to induce an inhomogeneous phase transition, synchronous shearing operations and gradient loading pressures were employed. Consequently, the phase-transition pressure of BC8-Si was reduced from >10 GPa, which is necessary for traditional static compression, to 1.4 GPa, and the average particle size was refined from 5 μm to 50 nm. Compared to micron-sized silicon, this system's bandgap shrank from 1.11 eV to 0.89 eV, its resistivity decreased by two orders of magnitude, its photogenerated carrier separation efficiency was significantly improved, and its photocurrent response increased by three orders of magnitude. These gains can be attributed to the direct bandgap character of BC8-Si, the optimization of nanoscale carrier-transport pathways, and the release of interfacial tensions caused by the shear. This technique overcomes the huge bandgap and high impedance constraints of conventional nanosilicon by combining outstanding electrical conductivity with structural stability. Technological support is provided for the large-scale preparation of high-performance materials, and the efficient synthesis of metastable-phase nanosilicon offers a suitable materials platform for high-efficiency optoelectronic devices.