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The lattice parameter of a single-crystal boron-doped synthetic diamond has been measured in the range 4.2-300 K by x-ray diffraction (Bond method), with precision . Over the whole range the results are consistent with Å, where T is the absolute temperature. The dilation due to doping indicates a boron concentration of about 100 ppm. The increase of thermal expansion over that of an undoped synthetic diamond is found to be unexpectedly large (10-15%), giving an apparent dilation on doping that is markedly temperature dependent.

We have measured low frequency generation-recombination noise ͑g-r noise͒ spectra of a heavily borondoped diamond crystal over the temperature range 20-300 K. The experimental results show that there are two peaks in the g-r noise spectrum at 120 K and 67 K, respectively. The 120 K peak corresponds to experimental evidence for existence of a hard gap having width of 10.4 meV. We interpret the 67 K peak as evidence for Wigner lattice formation whose gap width is 5.8 meV.