Needle-shaped and film- or plate-shaped black phosphorus single crystals were prepared by an improved bismuth-flux method. The conversion of red phosphorus to white phosphorus and the growth of black phosphorus single crystals from the solution of white phosphorus in liquid bismuth were performed in an evacuated quartz-glass apparatus without breaking the vacuum. Needle crystals measured about 5 mm in length and 10 to 100 µm in thickness. The thickness of film or plate crystals ranged from 1 to 10 µm and the width was usually above 100 µm, generally increasing with decreasing thickness. Some crystal morphologies were observed and analyzed crystallographically.

Systematic measurement of the electrical transport phenomena of black phosphorus grown by the all-closed bismuth-flux method has been performed in the range from room temperature down to 0.5 K for the electrical resistivity and down to 1.5 K for the Hall effect and the magnetoresistance effect. These samples exhibited p-type conduction with two types of acceptors, of which activation energies were 26.1 meV and 11.8 meV, respectively. The effective concentrations of acceptors were typically 1.36×1015 cm-3 for the deeper level and 0.44×1015 cm-3 for the shallower level. The maximum of the Hall mobility was found to be 2×104 cm2/Vs around 20 K. A new observation of n-type conduction below about 7 K for some of these samples suggested the existence of a surface inversion layer as a channel of electron conduction.

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PACS 71.35.-y, 78.55.Et Photoluminescence (PL) was circumstantially measured for ZnO single crystals with polar and non-polar faces. PL spectra of ZnO single crystals depended on the sector and polarity of ZnO single crystals. Emissions due to excitons from c-plane substrates sliced from the +c sector were strong, and FWHMs of the emissions were smaller than those from substrates sliced from the -c sector. An emission due to neutraldonor-bound exicitons (D 0 X) at 3.361 eV was dominantly observed on all surfaces of ZnO single crystals, and an emission due to ionized-donor-bound excitons (D + X) around 3.366 eV was observed on the O-face but not on the Zn-face at 4.2 K. It is thought that surface state densities due to oxygen caused this difference in PL emission for polarity of ZnO.

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