Photonic nanostructures for advanced light trapping in silicon solar cells: the impact of etching on the material electronic quality

Abstract

Dry plasma etching, commonly used by the Photonics community as the etching technique for the fabrication of photonic nanostructures, could be a source of device performance limitations when used in the frame of silicon photovoltaics. So far, the lack of silicon solar cells with state‐of‐the‐art efficiencies utilizing nanophotonic concepts shows how challenging their integration is, owing to the trade‐off between optical and electrical properties. In this study we show that dry plasma etching results in the degradation of the silicon material quality due to (i) a high density of dangling bonds and (ii) the presence of sub‐surface defects, resulting in high surface recombination velocities and low minority carrier lifetimes. On the contrary, wet chemical anisotropic etching used as an alternative, leads to the formation of inverted nanopyramids that result in low surface recombination velocity and low density of dangling bonds. The proposed inverted nanopyramids could enable high efficiency photonic assisted solar cells by offering the potential to achieve higher short‐circuit current without degrading the open circuit voltage. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Effect of Cryogenic Dry Etching on Minority Charge Carrier Lifetime in Silicon

“…This means that the plasma treatment of the silicon surface can destroy the crystal order in the subsurface region, leading to dangling bonds formation. In contrast, in a previous study, DLTS spectra also exhibited the responses from the deep center at high temperatures contrary to our experiments. Therefore, during the cryogenic ICP process, less degradation of silicon occurs due to lower ion bombardment.…”

“…It is correlated well with our DLTS spectra obtained for n-Si etched in SF 6 /O 2 gas mixture. The DLTS spectra in our study (Figure 7b) and in the study by Trompoukis et al [42] are similar, suggesting that the observed defect is related to the P b type. This means that the plasma treatment of the silicon surface can destroy the crystal order in the subsurface region, leading to dangling bonds formation.…”

“…No detailed study of the influence of the ICP process on defects in silicon was found. However, similar behavior of DLTS spectra was observed for RIE etching of n‐Si wafer with hydrogen and SF 6 /O 2 plasma . In both cases, plasma etching led to defect formation in the subsurface region.…”

“…However, similar behavior of DLTS spectra was observed for RIE etching of n-Si wafer with hydrogen [41] and SF 6 /O 2 plasma. [42] In both cases, plasma etching led to defect formation in the subsurface region. However, the process with SF 6 /O 2 plasma additionally led to deep-level defect appearance.…”

“…However, the process with SF 6 /O 2 plasma additionally led to deep‐level defect appearance. In the study by Trompoukis et al, silicon wafer after plasma treatment was investigated by the electron spin resonance (ESR) method and defects of P b type related to disorder silicon were observed. The thickness of the damaged layer was estimated by wet etching to be less than 50 nm.…”