Photo-Electrical Characterization of Silicon Micropillar Arrays with Radial p/n Junctions Containing Passivation and Anti-Reflection Coatings

In order to assess the contributions of anti-reflective and passivation effects in microstructured silicon-based solar light harvesting devices, thin layers of aluminum oxide (Al₂O₃), silicon dioxide (SiO₂), silicon-rich silicon nitride (SiN_x), and indium tin oxide (ITO), with a thickness ranging from 45 to 155 nm, are deposited onto regularly packed arrays of silicon micropillars with radial p/n junctions. Atomic layer deposition of Al₂O₃ yields the best conformal coating over the micropillars. The fact that layers made by low-pressure chemical vapor deposition (SiO₂ and SiN_x) are not conformally deposited on the sidewalls of the Si micropillars do not influence the photoelectrical efficiency. For ITO, a change in composition along the micropillar height is measured, which leads to poor performance. For Al₂O₃, deconvolution of the contributions of passivation and anti-reflection to the overall efficiency gain exhibits the importance of passivation in micro/nano-structured Si devices. Al₂O₃-coated samples perform the best, for both n/p and p/n configured pillars, yielding (relative) increases of 116% and 37% in efficiency of coated versus non-coated samples for p-type and n-type base micropillar arrays, respectively.