Synthesis And Characterization Of Superhard Semiconductor Boron Phosphide

Electronic information manufacturing is an important strategic industry,and its foundation is the research and manufacture of semiconductor.However,the performance of the first generation semiconductor represented by silicon and the second generation semiconductor represented by gallium arsenide in its various application fields has been approaching to its physical limits.In this context,it is particularly important to study next-generation semiconductors with high mobility,high thermal conductivity,wide bandgap,and capable of working at high temperature and in other hostile environments.Boron phosphide,BP,is such an attractive candidate with exceptional properties,which is,however,mainly limited to theoretical study because of the difficulty in sample preparation.In this work,we report the synthesis of large single-crystal BP in millimeter size.The final product has a zincblende structure and is optically transparent with a suitably large bandgap of 2.1 eV.Our experiment,in conjunction with ab initio theory,reveals that the compound exhibits an extraordinary strain stiffening,leading to an unexpectedly high load-invariant hardness of 37 GPa,close to the 40 GPa threshold for superhard materials and the hardest among the known semiconductors except diamond and cBN.Based on the first-principles calculations,the fracture mechanisms in BP under tensile and shear deformations can be attributed to the formation of metastable hexagonal phase.Further spectroscopy study indicates that an unusual electronic transition is occurred at high pressure of 13 GPa,resulting in asymptotically enhanced covalent bonding state.In addition,a phonon-assisted photoluminescence process and evidences for photon-pumped red lasing at 707 nm are also presented in detail.Findings in this work make BP as a benchmark material for diverse applications ranging from superhard tools to high-power lasing devices.