Enhanced free carrier generation in boron nitride films by pulsed laser radiation

A transient laser photoconductivity (PC) technique is applied to the: inves tigation of non-linear multi-photon excitation of mixed cBN/hBN films. A se lection of sub-micron thickness films on sapphire substrates with different stoichiometries were synthesized using ion-assisted and ECR-plasma CVD tec hniques. Efficient free carrier generation in these thin films is demonstra ted under nanosecond pulses excitation from VIS/UV harmonics of a Nd:YAG la ser. The effect is shown to be influenced largely by the nitrogen deficienc y and the carbon impurities present in the BN thin films. Both parameters a re responsible for the existence of donor and acceptor levels in the materi al. A laser generated 400 mV electrical signal was realized when using 200 nm boron-rich hBN films. A method for further enhancing the carrier generat ion efficiency via post-growth X-ray irradiation of the films is demonstrat ed. (C) 1999 Elsevier Science B.V. All rights: reserved.