Growth of Large Single Crystals of Black Phosphorus at High Pressures and Temperatures, and its Electrical Properties

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Abstract
The crystal growth of black phosphorus(B.P.) and its electrical properties have been studied at high pressures and high temperatures. A wedge type cubic anvil high pressure apparatus was used in the present experiments. From the measurement of the electrical resistance the melting points of B.P. have determined at high pressures. When B.P. is melted in the carbon furnace and slowly cools at 2.3 GPa, the large single crystals have often been grown. The size of the largest one is 4 mm in diameter and 5 mm in length. The anisotropic resistivity within the layers(ac-plane) has been observed. The resistivities along the a-, c- and b(perpendicular to the layer)-axes were about 0.1, ∼1 and 102∼103 Ωcm, respectively at atmospheric pressure. The resistivity along the a-axis was insensitive to pressure; on the other hand, the resistivities along the c- and b- axes decreased rapidly with increasing pressure at room temperature. The resistivity along the b-axis was about two orders of magnitudes larger than that of the a- and c- axes at 3.0 GPa. The intrinsic energy gaps observed in the single crystals were isotropic within the experimental error at atmospheric and high pressure. The electrical properties of B.P. are compared with the result of the band structure calculated by Asahina et al.