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

A transient laser photoconductivity (PC) technique is applied to the investigation of non-linear multi-photon excitation of mixed cBN/hBN films. A selection of sub-micron thickness films on sapphire substrates with different stoichiometries were synthesized using ion-assisted and ECR-plasma CVD techniques. Efficient free carrier generation in these thin films is demonstrated under nanosecond pulses excitation from VIS/UV harmonics of a Nd:YAG laser. The effect is shown to be influenced largely by the nitrogen deficiency and the carbon impurities present in the BN thin films. Both parameters are responsible for the existence of donor and acceptor levels in the material. A laser generated 400 mV electrical signal was realized when using 200 nm boron-rich hBN films. A method for further enhancing the carrier generation efficiency via post-growth X-ray irradiation of the films is demonstrated.