1,721,163 research outputs found
Surface passivation of black silicon phosphorus emitters with atomic layer deposited SiO2/Al2O3 stacks
No full textBlack silicon (b-Si) is a promising surface structure for solar cells due to its low reflectance and excellent light trapping properties. While atomic layer deposited (ALD) Al2O3 has been shown to passivate efficiently lightly-doped b-Si surfaces and boron emitters, the negative fixed charge characteristic of Al2O3 thin films makes it unfavorable for the passivation of more commonly used n+ emitters. This work studies the potential of ALD SiO2/Al2O3 stacks for the passivation of b-Si phosphorus emitters fabricated by an industrially viable POCl3 gas phase diffusion process. The stacks have positive charge density (Qtot = 5.5·1011 cm-2) combined with high quality interface (Dit = 2.0·1011 cm-2eV-1) which is favorable for such heavily-doped n-type surfaces. Indeed, a clear improvement in emitter saturation current density, J0e, is achieved with the stacks compared to bare Al2O3 in both b-Si and planar emitters. However, although the positive charge density in the case of black silicon is even higher (Qtot = 2.0·1012 cm-2), the measured J0e is limited by the recombination in the emitter due to heavy doping of the nanostructures. The results thus imply that in order to obtain lower saturation current density on b-Si, careful optimization of the black silicon emitter profile is needed.Peer reviewe
Recombination activity of light-activated copper defects in p-type silicon studied by injection- and temperature-dependent lifetime spectroscopy
No full textThe presence of copper contamination is known to cause strong light-induced degradation (Cu-LID) in silicon. In this paper, we parametrize the recombination activity of light-activated copper defects in terms of Shockley—Read—Hall recombination statistics through injection- and temperature dependent lifetime spectroscopy (TDLS) performed on deliberately contaminated float zone silicon wafers. We obtain an accurate fit of the experimental data via two non-interacting energy levels, i.e., a deep recombination center featuring an energy level at Ec−Et=0.48−0.62 eVEc−Et=0.48−0.62 eV with a moderate donor-like capture asymmetry (k=1.7−2.6) k=1.7−2.6) and an additional shallow energy state located at Ec−Et=0.1−0.2 eVEc−Et=0.1−0.2 eV, which mostly affects the carrier lifetime only at high-injection conditions. Besides confirming these defect parameters, TDLS measurements also indicate a power-law temperature dependence of the capture cross sections associated with the deep energy state. Eventually, we compare these results with the available literature data, and we find that the formation of copper precipitates is the probable root cause behind Cu-LID.Peer reviewe
Light-induced degradation in multicrystalline silicon: the role of copper
No full textIn this contribution, we provide an insight into the light-induced degradation of multicrystalline (mc-) silicon caused by copper contamination. Particularly we analyze the degradation kinetics of intentionally contaminated B- and Ga-doped mc-Si through spatially resolved photoluminescence (PL) imaging. Our results show that even small copper concentrations are capable of causing a strong LID effect in both B- and Ga-doped samples. Furthermore, the light intensity, the dopant and the grain qualitywere found to strongly impact the degradation kinetics, since faster LID was observed with stronger illumination intensity, B-doping and in the grains featuring low initial lifetime. Interestingly after degradation we also observe the formation of bright denuded zones near the edges of the B-doped grains, which might indicate the possible accumulation of copper impurities at the grain boundaries.Peer reviewe
Cu gettering by phosphorus-doped emitters in p-type silicon: Effect on light-induced degradation
No full textThe presence of copper (Cu) contamination is known to cause relevant light-induced degradation (Cu-LID) effects in p-type silicon. Due to its high diffusivity, Cu is generally regarded as a relatively benign impurity, which can be readily relocated during device fabrication from the wafer bulk, i.e. the region affected by Cu-LID, to the surface phosphorus-doped emitter. This contribution examines in detail the impact of gettering by industrially relevant phosphorus layers on the strength of Cu-LID effects. We find that phosphorus gettering does not always prevent the occurrence of Cu-LID. Specifically, air-cooling after an isothermal anneal at 800°C results in only weak impurity segregation to the phosphorus-doped layer, which turns out to be insufficient for effectively mitigating Cu-LID effects. Furthermore, we show that the gettering efficiency can be enhanced through the addition of a slow cooling ramp (-4°C/min) between 800°C and 600°C, resulting in the nearly complete disappearance of Cu-LID effects
Al-neal Degrades Al2O3 Passivation of Silicon Surface
Get PDFPublisher Copyright: © 2021 The Authors. physica status solidi (a) applications and materials science published by Wiley-VCH GmbHAtomic layer deposited (ALD) aluminum oxide (Al2O3) has emerged as a useful material for silicon devices due to its capability for effective surface passivation and ability to generate p+ region underneath the oxide as active or passive component in semiconductor devices. However, it is uncertain how Al2O3 films tolerate the so-called Al-neal treatment that is a necessary process step in devices that also contain silicon dioxide (SiO2) passivation layers. Herein, it is reported that the Al-neal process is harmful for the passivation performance of Al2O3 causing over eightfold increase in surface recombination velocity (SRV) (from 0.9 to 7.3 cm s−1). Interestingly, it is also observed that the stage at which the so-called activation of Al2O3 passivation is performed impacts the final degradation strength. The best result is obtained when the activation step is done at the end of the process together with the Al-neal thermal treatment, which results in SRV of 1.7 cm s−1. The results correlate well with the measured interface defect density, indicating that the Al-neal affects defects at the Si/SiOx/Al2O3 interface. The root causes for the defect reactions are discussed and possible reasons for the observed phenomena are suggested.Peer reviewe
Efficient surface passivation of black silicon using spatial atomic layer deposition
No full textNanostructured silicon surface (black silicon, b-Si) has a great potential in photovoltaic applications, but the large surface area requires efficient passivation. It is well known that b-Si can be efficiently passivated using conformal Atomic Layer Deposited (ALD) Al2O3, but ALD suffers from a low deposition rate. Spatial ALD (SALD) could be a solution as it provides a high deposition rate combined with conformal coating. Here we compare the passivation of b-Si realized with prototype SALD tool Beneq SCS 1000 and temporal ALD. Additionally, we study the effect of post-annealing conditions on the passivation of SALD coated samples. The experiments show that SALD passivates b-Si surfaces well as charge carrier lifetimes up to 1.25 ms are obtained, which corresponds to a surface recombination velocity Seff,max of 10 cm/s. These were comparable with the results obtained with temporal ALD on the same wafers (0.94 ms, Seff,max 14 cm/s). This study thus demonstrates high-quality passivation of b-Si with industrially viable deposition rates.Peer reviewe
Impact of Standard Cleaning on Electrical and Optical Properties of Phosphorus-Doped Black Silicon
No full textBlack silicon (b-Si) has been estimated to considerably grow its market share as a front texture of high-efficiency silicon solar cells. In addition to excellent optical properties, high-efficiency cell process requires extreme cleanliness of the bulk material, and thus cleaning of b-Si surfaces is often a critical process step. While standard clean (SC) 1 solution efficiently removes possible contamination from wafer surfaces, we show here that it may cause challenges in b-Si solar cells. First, the silicon etch rate in SC1 solution is shown to depend on the phosphorous concentration and as high rate as ∼1.4 nm/min is observed on planar emitter surfaces. When extending the study to b-Si, which has much larger surface area in contact with the cleaning solution, even higher volumetric Si consumption occurs. This is observed in significant changes in emitter doping profiles, for instance, a 10 and 30-min cleaning increases the sheet resistance from 47 to 57 Ω/□ and 127 Ω/□, respectively. Furthermore, the SC1 solution alters substantially the nanostructure morphology, which impacts the optics by nearly doubling and more than tripling the surface reflectance after a 30 and 60-min immersion, respectively. Thus, uncontrolled cleaning times may impair both the electrical and optical properties of b-Si solar cells.Peer reviewe
Nanostructured germanium with >99% absorption at 300-1600 nm wavelengths
No full textTarkista embargo, kun artikkeli julkaistu. | openaire: EC/H2020/777222/EU//ATTRACTNear-infrared (NIR) sensors find numerous applications within various industry fields, including optical communications and medical diagnostics. However, the state-of-the-art NIR sensors made of germanium (Ge) suffer from rather poor response, largely due to high reflection from the illuminated device surface. This work demonstrates a method to increase the sensitivity of Ge sensors by implementing nanostructures to the wafer surfaces. The absorbance of nanostructured Ge wafers is measured to be >99 % in the whole UV-VIS-NIR spectrum up to 1600 nm wavelength, which is a significant improvement to bare Ge wafers that reach absorption of only 63 % in maximum. The process is shown to be capable of producing uniform nanostructures covering full 100-mm-diameter substrates as well as wafers with etch mask openings of different sizes and shapes, which demonstrates its applicability to CMOS sensor manufacturing. The results imply that nanostructured Ge has potential to revolutionize the sensitivity of Ge-based sensors.Peer reviewe
Low-T anneal as cure for LeTID in Mc-Si PERC cells
No full text| openaire: EC/FP7/307315/EU//SOLARXLight and elevated temperature induced degradation (LeTID) is known to be affected by the last dark anneal that the silicon wafers or cells experience prior to illumination. Here we study how low-temperature dark anneal performed on fully processed multicrystalline silicon (mc-Si) passivated emitter and rear solar cells (PERC) influences LeTID characteristics, both the intensity of the degradation and the degradation kinetics. Our results show that a relatively long anneal at 300 °C provides an efficient means to minimize LeTI D while too short dark anneal at the same temperature seems to have a negative impact on the subsequent degradation under light soaking. Finally, we compare the experimental results with the model originally developed for metal precipitation and discuss the possibility of metals being involved in LeTID mechanism.Peer reviewe
Tailoring Femtosecond-Laser Processed Black Silicon for Reduced Carrier Recombination Combined with >95% Above-Bandgap Absorption
No full textThe femtosecond-pulsed laser processed black silicon (fs-bSi) features high absorptance in a wide spectral range but suffers from high amount of laser induced damage as compared to bSi fabricated by other methods. Here, we aim to minimize the charge carrier recombination in the fs-bSi caused by laser damage as indicated by the sub-bandgap absorption and as quantified by the carrier lifetime, while maintaining high absorption in the above-bandgap. The effect of the laser parameters, including the focal position, the average power, and the scan speed are systematically studied by characterizing the surface morphology, the absorptance spectra, and the minority-carrier recombination lifetime. For the surface passivation of fs-bSi we use the well-established atomic layer deposited (ALD) Al2O3. The results show that with the tailored laser parameters, high average absorptance of about 96% in the visible range and minority carrier lifetime of 54 μs at the injection level of Δn = 1 ∙ 1015 cm−3 can be obtained simultaneously. This work paves the way towards high-performance broadband optoelectronic devices based on surface passivated fs-bSi.Peer reviewe
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