Enhanced Light Scattering by Preferred Orientation Control of Ga Doped ZnO Films

What is it about?

We have explored the effective approach to fabricate GZO/ZnO films that can make the pyramidal surface structures of GZO films for effective light scattering by employing a low temperature ZnO buffer layer prior to high temperature GZO film growth. The GZO thin films exhibit the typical preferred growth orientations along the (002) crystallographic direction at deposition temperature of 400°C and SEM showed that column-like granule structure with planar surface was formed. In contrast, GZO films with a pyramidal texture surface were successfully developed by the control of (110) preferred orientation. We found that the light diffuse transmittance of the film with a GZO (800 nm)/ZnO (766 nm) exhibited 13% increase at 420 nm wavelength due to the formed large grain size of the pyramidal texture surface. Thus, the obtained GZO films deposited over ZnO buffer layer have high potential for use as front TCO layers in Si-based thin film solar cells. These results could develop the potential way to fabricate TCO based ZnO thin film using MOCVD or sputtering techniques by depositing a low temperature ZnO layer to serve as a template for high temperature GZO film growth. The GZO films exhibited satisfactory optoelectric properties.

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Why is it important?

In this work, we explored the methodology to increase the light diffuse transmittance through controlling the preferred orientation of polycrystalline Ga doped ZnO (GZO) films grown by the low-pressure chemical vapor deposition (LPCVD) technique using diethyl zinc (DEZn) and trimethyl gallium (TMGa) as the Zn and Ga precursors, respectively. Different from the low process temperature (~150°C) of B-doped ZnO, the GZO films exhibited satisfactory optoelectric properties at reaction temperatures as high as 400°C. X-ray diffraction measurement indicated that major growth direction was (002) plane and secondary electron microscopy showed that column-like granule structure with planar surface was formed. By depositing a low temperature ZnO layer to serve as a template for high temperature GZO film growth, the main preferred orientation of the GZO films was manipulated to (110) plane and the film surface to the pyramid-like structure. Through this two-step growth, the light diffuse transmittance of the film with a GZO (~800 nm)/ZnO (766 nm) combination exhibited 13% increase at 420 nm wavelength due to the preservation of the pyramidal surface morphology.

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