The electrical resistivity, Hall coefficient, and thermoelectric power of microscopic boron single crystals have been measured as a function of temperature. Rectification and photoconductivity effects were observed at room temperature. The large majority of these single crystals had a high resistivity (about 1.7×${10}^6$ ohm cm at 300°K) which decreased by a factor of nearly ${10}^{10}$ as the temperature was increased from 200°K to 1000°K. A few crystals, however, had a much lower resistivity at 300°K (less than 100 ohm cm) and at this temperature their resistivity decreased much more slowly with increasing temperature. Such behavior is attributed to donor impurity levels. From data in the high-temperature range (800°K to 1000°K) the energy gap between the filled band and conduction band was calculated to be 1.55±0.05 ev. Hall, thermoelectric, and rectification studies indicated that hole conduction predominated for all crystals at high temperatures but that electron conduction predominated for the low-resistivity crystals near 300°K. The mobilities of the charge carriers at 300°K were found to be the order of one ${\mathrm{cm}}^2$ ${\mathrm{volt}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ with the hole mobility the larger. Non-ohmic conduction was observed and shown to arise from Joule heating.

• Received 1 October 1956

DOI:https://doi.org/10.1103/PhysRev.107.419