Properties of amorphous boron nitride thin films

Amorphous boron nitride films were prepared by very high frequency plasma chemical vapour deposition. The material obtained was stoichiometric and the choice of preparation conditions (substrate temperature, gas phase pressure) critically affected hydrogen concentration and bonding. The films showed a bandgap of typically 5 eV. A considerable density of electronic states in the bandgap and fairly flat band tails were revealed by photothermal deflection spectroscopy. The electric break-through field strength was about 2.2 MV/cm. From the dependence of the infrared absorption on the substrate temperature, an IR absorption band at 910 cm ^-1 was attributed to the wagging mode of the BH vibration. The amorphous phase of BN consists almost exclusively of sp ² bonding. In samples which contain sp ³ bonding also the formation of a crystalline phase is detected by X-ray diffraction.