Optical properties of β-Si3N4 single crystals grown from a Si melt in N2

Large colored beta-Si3N4 single crystals were successfully grown from a Si melt in N-2. The transmission optical absorption of coloring beta-Si3N4 single crystal shows that impurities introduce a midgap level of similar to 2.4 eV into the wide band gap of similar to 5.3 eV in nondoped Si3N4. The infrared transmission spectrum and electron probe x-ray microanalysis of beta-Si3N4 samples show that the solution of the Al element affects the silicon-nitrogen molecular vibration and the states within the band gap of beta-Si3N4. The obtained results mean that the Al impurity acts as the radiative center and is the origin of the color in the beta-Si3N4 single crystal. (C) 1999 American Institute of Physics. [S0003-6951(99)02823-5].