Role of laser pulse duration and gas pressure in deposition of AlN thin films

We investigated the relative merits and limits of pulsed laser deposition f rom AlN targets in vacuum and low-pressure nitrogen in obtaining stoichiome tric and crystalline aluminum nitride thin films. We used two UV excimer la ser sources (lambda =248 nm): a nanosecond system (tau (FWHM)=30 ns) and, a subpicosecond (tau (FWHM)=450 fs) system. The obtained structures were cha racterized by x-ray diffraction, electron microscopy in cross section, sele cted area electron diffraction, and profilometry. We demonstrated that the best results are obtained with the sub-ps laser source in vacuum and in low pressure nitrogen when the AlN thin films are very pure, crystalline, clea rly exhibiting a tendency to epitaxy. Metallic Al is present in the films d eposited with the ns laser source. We believe this is an effect of the grad ual decomposition of AlN inside the crater on the target surface under mult ipulse laser irradiation. (C) 2001 American Institute of Physics.