Crystallinity and electrical properties of hydrogenated microcrystalline silicon germanium by RF-PECVD for solar cell application

The deposition process of hydrogenated microcrystalline silicon germanium (μc-SiGe:H) film is developed with Applied Materials' AKT4300 PECVD system (substrate size: 600×720mm²) at the deposition rate up to 5Å/s. The crystallinity and the chemical composition are characterized with Raman scattering spectroscopy and X-ray diffraction (XRD) analysis. The peak shift of the Si-Si transverse optic (TO) vibration modes by Raman spectra indicates the incorporation of Ge atoms. The peak of the (220) plane by the XRD also shifts to smaller 2-theta value due to increased interplanar spacing. The grain size is calculated around 80~90Å based on the (220) peak position and full width at half maximum (FWHM) and verifies that the film is microcrystalline. The temperature dependent dark and photo conductivity are measured around 1×10^-7 and 1×10^-5 S/cm respectively which are within the range of microcrystalline. The activation energy is deduced around 1.1~1.2 eV. The incorporation of Ge atoms changes the crystallinity and electrical properties of the microcrystalline silicon film accordingly while maintains the deposition rate and makes it promising to improve the film quality as the absorber layer in the multi-junction solar cell.