Effect of MACE Parameters on Electrical and Optical Properties of ALD Passivated Black Silicon

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 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.

Recent Progress of Black Silicon: From Fabrications to Applications

“…Additionally, the thickness has little influence on the reflectivity, but the increase of thickness will increase the stability of the reflectivity. In 2019, K. Chen et al [ 53 ] fabricated black silicon by MACE, and the researchers studied the effect of silver ion concentration on the optical and electrical performances of the material in the etching solution. The results show that the silver ion concentration has an effect on the porosity of black silicon samples, and the lower concentration of silver ion can improve the electrical performance, but has some damage to the optical performance.…”

“…( d ) Different etching time in high concentration Ag + solution. Adapted from reference [ 53 ], with permission from IEEE © 2020.…”

“…The results express that the longer the time from 20 s to 180 s, The researchers not only used MACE to fabricate black silicon, but also explored the optimization of the preparation process [46] through experiments. When a different etching time [54,55], solution metal ion density [53], or substrate thickness are used, the fabricated black silicon sample will have different optical properties.…”

Black-Silicon Ultraviolet Photodiodes Achieve External Quantum Efficiency above 130%

“…While there might be some concerns about the industrial applicability of the nanostructures, it has been shown that the black-Si nanostructures survive well in the industrial mass production lines [47] and their manufacturing costs can be competitive even in the cost-driven photovoltaics industry [48]. Furthermore, there are also alternative cheaper nanotexturing technologies available, such as metal assisted chemical etching, that can be considered [49,50].…”

Effects of silver nanoparticles layer thickness towards properties of black silicon fabricated by metal-assisted chemical etching for photovoltaics

“…2. Details on the mathematical equations of current density of the cathodic process and chemical equations of the two half reactions of the redox couple (reactions at cathode and anode) can be found in related literatures [25][26][27]. From Fig.…”