Influence of the precursor materials on the process of aluminium induced crystallisation of a-Si and a-Si:H

Thin films of poly-Si on low cost substrates such as glass are attractive for thin film solar cells and other large-area electronic devices. The controlled and reproducible preparation of polycrystalline silicon thin films by aluminium-induced crystallisation (AIC) needs optimization of both the process of crystallisation and the deposition conditions of the precursor silicon and aluminium layers. In this work, the influence of the hydrogen concentration in the precursor amorphous silicon layer and the deposition temperature of the aluminium layer on the structural properties of poly-Si thin films obtained by AIC of un-hydrogenated (a-Si) and hydrogenated amorphous silicon films (a-Si:H) are studied. Stacks of glass/a-Si:H/Al were prepared for performing the AIC process. The aluminium and amorphous silicon films are deposited by rf magnetron sputtering. The hydrogen concentration in the a-Si:H films is varied from 0 to 18 at.%. The substrate temperature during a-Si (a-Si:H) deposition is kept constant at 250 °C. The Al film is deposited on top of the a-Si (a-Si:H). The deposition temperature of the aluminium films (TSAl) is varied from room temperature (RT) to 500 °C. The samples are isothermally annealed in air at Tan = 530 °C for 7 h. The structural properties of the poly-Si films are studied by Raman spectroscopy and optical microscopy. The results indicate that the hydrogen concentration in the precursor a-Si:H is a very important parameter. It is also observed that TSAl influences the structural properties of the poly-Si films. It is found that films with better crystalline structure are obtained when the a-Si:H precursor layers contain 9 at.% hydrogen and the aluminium deposition temperature is about 350 °C.