High Temperature Crystallization Process of a-Si Thin-films on Aluminum Nitride Substrates

Abstract

Crystallization of silicon (Si) from amorphous silicon (a-Si) on foreign substrates has been studied by various research institutes. Crystallization of silicon thin-films on foreign substrates acts as an active layer in silicon thinfilm solar cells. In this research, due to the compatibility of thermal stability and expansion coefficient with Si, we used an aluminum nitride (AIN) substrate as an alternative candidate to glass and other ceramic substrates. P-type amorphous Si 5 μm thin-film was deposited using an ebeam evaporator directly on AIN substrates. The deposited layer was annealed at high temperature (°C) with N2 environment in a conventional tube furnace. Optical characterization was done using an optical microscope to investigate the surface morphology of as-grown and annealed samples. A smoother surface with an average grain size of about 3–4 μm was formed after annealing. Reflectance parameters were measured by UV-vis spectrometry. UV-vis-NIR was studied on as-grown and annealed samples to calculate the quality factor of the Si thin-film which was about 84.4 %. X-ray diffraction (XRD) was used to determine the phase direction of the Si thin-film before and after thermal annealing. It was observed that FWHM varied from 7.73 to 9.30 cm−1, Raman shift was from 520 to 522 cm⁻¹, and the stressed level also changed from 180 to 540 Mpa after annealing at high temperature for a long time. Interestingly, a crystallinity fraction was achieved of about 90 % at 1100 °C.