Effects of synchrotron x-rays on PVD deposited and ion implanted α-Si

We have studied the effects of intense x-ray irradiation on the structure of amorphous Si films. The films were obtained by either physical vapor deposition or by implantation of high energy ions into crystalline Si. They were exposed to different total doses of synchrotron x-rays. From the EXAFS and EXELFS measurements we find that an exposure to x-rays increases the Si coordination number. Also in the PVD films a prolonged x-ray exposure enlarges, by about 2%, the Si-Si bond length. Raman spectroscopy shows that Si amorphized with high energy ions contains small residual amounts of crystalline material. Irradiation of such films with x-rays annihilates those crystallites resulting in homogeneously amorphous layer with a close to four-fold coordination of Si atoms. This rearrangement of the local structure has a pronounced effect on the crystallization process of the amorphous films. Thermal annealing of x-ray irradiated ion amorphized films leads to nearly defect free solid phase epitaxy at 500°C. Also we observe a delay in the onset of the crystallization process in x-ray irradiated PVD films. We associate this with a reduced concentration of nucleation centers in the x-ray treated materials.