A NEAR-IR IQE IMPROVEMENT OBTAINED BY Si STRUCTURAL MODIFICATIONS

摘要

One of the most important conversion efficiency limitations of Si concerns its bandgap value and its indirect bandgap transitions. We suggest that these two limitations can be partially overcome by nanoscale modifications of the material made possible by defect engineering for advanced semiconductor devices within a concept of third generation solar cell. P ion implantation at 180 keV has been used to create an amorphized nanolayer within the bulk of a good crystalline Si solar cell. The ion beam modifications had to be followed by a thermal treatment in order to obtain sharp a-Si/c-Si heterointerfaces and a homogeneous a-Si nanostructure. For implanted cells we observed a near-IR IQE improvement (between 900 and 1200 nm) in comparison with excellent classical cells. The increase IQE can be deconvoluted into four different characteristic energies that are supposedly related to an extrinsic energy band within the band gap. The amelioration depends on the duration of the post-implantation annealing. The influence of the ambient temperature suggests the participation of phonons.