Effect of Si incorporation to produce Ge-rich nc-SixGe1-x absorber layer for nc-Si solar cells

Nanocrystalline silicon germanium (nc-SiGe) thin films has been attracted increased attention for useful applications as infrared absorber layer at the bottom cell of multi-junction nc-Si solar cells. In the present work, Ge-rich nanocrystalline silicon-germanium alloy (nc-SixGe1-x) films have been grown by conventional RF-PECVD, by efficiently incorporating Si into the low temperature (220 degrees C) grown highly conducting nc-Ge matrix having good crystallinity. The influence of the incorporation of Si was studied by XRD, Raman, optical absorption and electrical conductivity measurements. The nc-SixGe1-x film prepared with an optimum flow ratio of the precursor gases, SF = [SiH4] / [(GeH4) + (SiH4)] = 0.1, demonstrating narrow band gap similar to 1.23 eV, good electrical conductivity similar to 4.72 x 10(-4) S.cm(-1), corresponding low activation energy similar to 167 meV and reasonable crystallinity with an intensity ratio of <220> to <111> crystallographic orientation similar to 0.66, seems significantly potential as an absorber layer to use as the bottom cell of tandem-type nc-Si solar cell.