Opto-electronic properties of different black silicon structures passivated by thermal ALD deposited Al_2O_3

Martin Otto, Matthias Kroll, Thomas Käsebier, Xiaopeng Li, Benjamin Gesemann, Kevin Füchsel, Johannes Ziegler, Alexander N. Sprafke, Ralf Wehrspohn
2013 Renewable Energy and the Environment   unpublished
 Abstract-Metal-assisted chemical etching (MACE) enables efficient texturing of diamond-wire sawn multicrystalline silicon (mc-Si) wafers. However, the excellent optics are often sacrificed by polishing the surface to achieve better surface passivation with chemical-vapor-deposited (CVD) silicon nitride (SiNx). In this work, we show that a polishing step is not required when CVD SiNx is replaced with atomic-layer-deposited (ALD) aluminum oxide (Al2O3). Indeed, while polishing increases
more » ... g increases reflectance, it has in general only very modest effect on surface recombination velocity of ALD-passivated b-Si. Furthermore, since ALD Al2O3 is compatible with various surface morphologies due to its excellent conformality, the MACE parameters can be more freely adjusted. First, the concentration of silver nitrate (AgNO3) in AgNO3/H2O solution that is used to deposit Ag nanoparticles is shown to affect the final b-Si morphology. Instead of needle-shaped b-Si produced by 5 mmol/L AgNO3 concentration, two orders of magnitude lower AgNO3 concentration produces porous structures, which are more challenging to passivate. Additionally, we demonstrate that a separate Ag nanoparticle removal step in nitric acid (HNO3) is not a prerequisite for high carrier lifetime. Instead, Ag nanoparticles present during polishing in a HF/HNO3/H2O solution affect the final b-Si morphology by accelerating the etching of Si. The results demonstrate that no trade-offs are necessary between optical and electrical properties of MACE b-Si when using ALD. Index Terms-black silicon, nanostructure, metal assisted chemical etching, atomic layer deposition All authors are with the
doi:10.1364/pv.2013.pm1c.3 fatcat:khrtoxlcbzbonlmsrmvzr47rvi