The effect of substrate temperature and interface oxide layer on aluminum induced crystallization of sputtered amorphous
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The effect of substrate temperature and interface oxide layer on aluminum induced crystallization of sputtered amorphous silicon Maruf Hossain*, Husam Abu-Safe, Marwan Barghouti, Hameed Naseem & William D. Brown Arkansas Advanced Photovoltaic Research Center, Department of Electrical Engineering 3217 Bell Engineering Center, University of Arkansas, Fayetteville, Arkansas 72701
ABSTRACT The effect of substrate temperature and interface oxide layer on aluminum induced crystallization (AIC) of amorphous silicon (a-Si) is investigated. The effect of substrate temperature on the AIC process was studied by changing the deposition temperate of a-Si from 200 to 300ºC in a Al/a-Si/glass configuration. To study the effect of interface oxide on AIC, samples with a-Si/Al/glass, a-Si/Al-oxide/Al/glass, and Al/Si-oxide/a-Si/glass configurations were prepared at a fixed substrate temperature. The samples were annealed in the temperature range from 300ºC to 525ºC for different periods of time. The X-ray diffraction (XRD) patterns confirmed the crystallization of the a-Si films in the various configurations. From the analysis, we report that crystallization of a-Si happen at 350ºC annealing temperature in the Al/a-Si/glass configuration. However, with or without the presence of Si-oxide at the interface, crystallization saturated after annealing for 20 minutes at 400ºC. On the other hand, when Al-oxide is present at the interface, higher annealing temperatures and longer annealing times are required to saturate the crystallization of a-Si. Environmental Scanning Electron Microscope (ESEM) and Energy Dispersive X-Ray (EDX) mapping were used to study the surface morphology as well as the layer sequence after crystallization. This analysis revealed that Si-Al layer-exchange happens regardless of the deposited film configuration.
INTRODUCTION Polycrystalline silicon (pc-Si) thin film solar cells and transistors are being widely investigated nowadays. For thin film solar cells pc-Si is the most promising material in reducing the production cost [1]. In order to use this material to fabricate low cost devices, reduced processing temperature is required. At low processing temperature, low cost glass or plastic substrate can be used to fabricate thin film solar cells. Pc-Si thin films can be fabricated by crystallization of amorphous silicon. Solid phase crystallization (SPC) of a-Si occurs with annealing for 24 hours at 600ºC. With the help of a metal, this crystallization temperature can be reduced dramatically. With Al, the crystallization process can be initiated with temperature as low as 150ºC [2]. Lot of research has been focused on AIC using different a-Si deposition techniques. Among those techniques, plasma enhanced chemical vapor deposition (PECVD) has been used extensively [2-7]. Different researchers have studied AIC of hydrogenated a-Si (aSi:H) using this technique in the sequence of Al/a-Si:H/glass [2]. Haque et. al. [2] observed that aluminum induced crystallization of a-Si:H for this configuration occurred at tem
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