Papers by Keyword: Black Silicon

Abstract: In this work, the impacts of wafer doping type on structural and optical properties of black silicon (b-Si) fabricated by metal-assisted chemical etching (MACE) process are investigated. P-type and n-type mono-crystalline silicon (mono c-Si) wafers are etched in an aqueous solution of hydrofluoric acid (HF), silver nitrate (AgNO₃) and deionised water (DI H₂O) at room temperature and various durations from 5-20 minutes. Surface morphological results demonstrate the formation of b-Si nanowires (NWs) with average lengths of 0.4-0.8 μm for p-type wafers and 0.8-3.0 μm for n-type wafers. The higher length of the NWs for the n-type wafers is due to the minority charge carriers, which lead to a higher etching rate during the MACE process. Within the 300-1100 nm wavelength region, weighted average reflection (WAR) for the p-type and n-type wafers decreases to 6.6% and 6.4%, respectively, after 20 minutes of etching. The corresponding improvement in broadband light absorption results in maximum potential short-circuit current density (J_{sc (max)}) of 38.2 and 38.8 mA/cm² for the p-type and n-type b-Si, respectively, which is an of enhancement of 39.9% and 42.1% when compared to the J_{sc (max)} of planar c-Si reference.

Abstract: This paper reports the temperature and the concentration dependence of anisotropic etching for (100) p-Silicon in an aqueous KOH solution etching rate of wet etching has been experimentally determined with varying concentrations and the temperature of the KOH solution. The texturing process was managed at different etching durations ( 20 min, 40 min, and 60 min). XRD test showed that the lowest value of grain size was 5.0 nm (obtained with the highest porosity percentage of 50% with 4.5% KOH concentration for 60 min). FESEM test showed that the pore diameter increased with increasing etching time. The lowest reflectance value was (2.8 % at 550 nm wavelengths for samples treated with 4.5% KOH concentration for 60 min etching time. The refractive index value was 1.8 for the same black Si sample, also Hall test is introduced.

Abstract: The aim of this study is to determine whether the effective medium approach (EMA) is suitable to model black silicon structures. The present study focuses on comparing EMA paired with 1D FDTD simulations to full 3D FDTD simulations. Comparison was done for ordered cylindrical and hemispherical b-Si nanostructures. From the simulation results, the 1D simulation seems to underestimate the transmittance and overestimate the reflectance for these structures. This was attributed to the failure of the EMA to capture scattering and diffraction effects that were present in the nanostructures. The absorptance spectrum was comparable for both 1D and 3D simulations, hence it was concluded that the simplification may be suitable for simplifying problems where calculating the absorption of light is desired.

Abstract: This work investigates properties of Poly (3,4-ethylenedioxythiophene)–poly (styrene sulfonate) (PEDOT:PSS) on black silicon (nanotextured) and hybrid textured (nanotextured/microtextured) surfaces. The black silicon (b-Si) surface is fabricated using two-step metal-assisted chemical etching (MACE) process on crystalline silicon (c-Si) while the hybrid textures are fabricated using two-step MACE process on microscale pyramids. With PEDOT:PSS, weighted average reflection (WAR) reduces from 9.2% to 7.7% for b-Si and from 7.2% to 5.2% for hybrid textures. This is due to the anti-reflective (AR) property of the polymer. Electrical characterizations of the PEDOT:PSS layer reveal higher sheet resistance (R_s), lower hole concentration (n_h) and improved mobility (μ_h) with the presence of the surface textures on c-Si, in comparison to the results from planar c-Si reference.

Abstract: This paper reports broadband anti-reflection in black silicon (b-Si) fabricated by two-step metal-assisted chemical etching (MACE) for potential photovoltaic (PV) applications. The method involves deposition of silver nanoparticles (Ag NPs) in aqueous solution of HF:AgNO₃, followed by etching in HF:H₂O₂:DI H₂O solution for different duration (10-25 s). Effects of etching time towards surface morphological and optical properties of b-Si nanowires are investigated. Surface morphological characterization confirms presence of b-Si nanowires with heights of 350-570 nm and diameter of 150-300 nm. The b-Si nanowires exhibit outstanding broadband anti-reflection due to refractive index grading effect. This is represented as weighted average reflection (WAR) in the 300-1100 nm wavelength region. After 20 s of etching, b-Si nanowires with height of 570 nm and width of about 200 nm are produced. The nanowires demonstrate WAR of 5.5%, which represents the lowest WAR in this investigation. This results in absorption of 95.6% at wavelength of 600 nm. The enhanced broadband light absorption yields maximum potential short-circuit current density (J_sc(max)) of up to 39.7 mA/cm², or 51% enhancement compared to c-Si reference. This facile b-Si fabrication method for broadband enhanced anti-reflection could be a promising technique to produce potential PV devices with high photocurrent.

Abstract: This paper examines the influence of etching regimes on the reflectance of black silicon formed by Ni-assisted chemical etching. Black silicon exhibits properties of high light absorptance. The measured minimum values of the reflectance (R-min) of black silicon with thickness of 580 nm formed by metal-assisted chemical etching (MACE) for 60 minutes at 460 lx illumination were 2,3% in the UV region (200–400 nm), 0,5% in the visible region (400–750 nm) and 0,3% in the IR region (750–1300 nm). The findings showed that the reflectance of black silicon depends on its thickness, illumination and treatment duration. In addition, the porosity and refractive index were calculated.

Abstract: Thin Al₂O₃ films were deposited on p-type black silicon (b-Si) by using chemical liquid phase deposition (CLD) technique. The influence of annealing temperatures on the structural and optical properties of Al₂O₃ films was investigated. The b-Si with 80-nm Al₂O₃ films exhibits a low total reflectance of 5%. The sample annealed 300 °C exhibits negative fixed charge with the density of 1.5×10¹² cm^-2. With the increasing of annealing temperature, negative shift of C-V curve was observed, indicating the polarity of fixed charge changes to positive, with maximal the density of 8.7×10¹¹ cm^-2. The evolution of the polarity of fixed charge is assigned to the decreasing of O: Al ratio caused by the transition of the crystalline type of Al₂O₃. The change of fixed charge polarity in Al₂O₃ provides a feasible route for both p- and n-type Si passivation in Si solar cells by adjusting the thermal post-treatment.

Abstract: The very low efficiency of solar cells can be attributed to a plethora of reasons. The most important reason being, reflection of sunlight from the solar cell surface. Most of the sunlight incident on the solar cells gets reflected back due to the smooth surface of the silicon wafers. This paper presents a novel method to avoid this by using black silicon solar cells. Black silicon tends to make use of the concept of black body radiation to absorb all the rays incident on it and thereby reducing the reflectivity of the solar cell. The nano-fabrication technique involves usage of special wet-etch techniques to achieve nano-sized pores on the surface of silicon. In case of normal solar cells, usually layers of a suitable anti-reflective coating are given which tend to minimize the amount of reflection. This unfortunately increases the manufacturing cost. The unfavourable conditions of heat and dirt further tend to soil the layer of anti-reflective coating, reducing the gains of anti-reflective coating. Thus, black silicon solar cells provide better efficiency while simultaneously reducing the fabrication cost.

Abstract: A kind of hill-like black silicon have been designed and fabricated by using the combination method of KOH anisotropic etching and gold-assisted HF etching. Pillars array on the surface of a silicon sample was obtained by KOH etching with a SiN_x film dots pattern used as a mask. The sample was then etched in the oxidant HF solution catalyzed by Au nanoparticles for 5 minutes. The etched sample appears dark black. This black silicon is orderly hill-like textures in micro-scale with density nanopores on them. It can suppress the reflection to less than 4% in wavelength range from 250nm to 1000nm, and to about 2.5% at the wave number of 2000-4000 cm^-1. It also has high additional absorption in IR range.

Abstract: This paper investigates the influence of different number of laser pulses on contact behavior and conductivity of the surface layer of femtosecond laser microstructured, sulfur-doped silicon. Single shot laser processed silicon (Pink Silicon) is characterized by low surface roughness, whereas five shot laser processed silicon (Grey Silicon) has an elevated sulfur content with a surface roughness low enough to maintain good contacting. To laterally confine the laser induced pn-junction part of the Grey Silicon sample surface is etched off. The etching depth is confirmed to be sufficient to completely remove the active n-type sulfur layer. While Pink Silicon shows little or no lateral conductivity within the laser processed layer, Grey Silicon offers acceptable conductivity, just as expected by the fact of having incorporated a higher sulfur dopant content. Recombination dominates the irradiated regions of Pink Silicon and suppresses excess charge carrier collection. Grey Silicon, while showing sufficient lateral conductivity, still shows regions of lower conductivity, most likely dominated by the laser irradiation-induced formation of dislocations. According to our results, the optimum laser pulse number for electrical and structural properties is expected to be in the range between one and five laser pulses.