Surface Morphology Of Silicon Research Articles

Effects of Black Silicon Surface Morphology Induced by a Femtosecond Laser on Absorptance and Photoelectric Response Efficiency

In this study, the effects of variations in the height (h) and bottom radius (r) of black silicon microstructures on their absorptance and photoelectric response efficiency were analyzed. By using the relation cot⁡θ2=hr to combine the parameters, it was found that changes in morphology affected the absorptance of black silicon microstructures, with h being directly proportional to the absorptance, while r was inversely proportional. A positive correlation was observed between cot⁡θ2 and absorptance. However, the correlation between cot⁡θ2 and photoelectric response efficiency was not significant. Through Raman spectroscopy analysis of the samples, it was concluded that as the laser ablation energy density increased, more lattice defects were introduced, weakening the charge carrier transport efficiency. This study further elucidated the mechanism by which microstructural changes impacted the absorptance and energy density of black silicon, providing valuable insights for optimizing its energy density.

Enhancement in the Stability of Porous Silicon Using Electrochemical Grafting of Polymer 2,6 Dihydroxy Naphthalene

While there have been many advancements related to porous silicon, the reactivity of silicon with the ambient (particularly in environments with oxygen and humidity) has limited its use and integration in a wide variety of applications. Therefore, it is important to passivate the surface of nanostructured/porous silicon. To this end, there have been many reports in literature where passivation of bare (or unpassivated) porous silicon (UPSi) surface has been performed using gas phase techniques (thermal carbonization) and solution-based methods. In this work, we have studied the influence of the electrochemical deposition of polymer 2,6 dihydroxynaphthalene (2,6 DHN), in enhancing the stability of porous silicon surfaces.Porous silicon was synthesized by the electrochemical etching of pre-cleaned p-type silicon substrates with resistivity of about 0.001 Ω-cm to 0.005 Ω-cm, in a PTFE cell that we have fabricated, with 48% HF and ethanol mixture (7:3) as the electrolyte solution, at a current density of about 1.08 A/cm². The polymer solution used for electrodeposition was prepared as a solution of 1 mM 2,6-dihydroxy naphthalene (2,6-DHN) in 100 mL of 1x phosphate buffer solution, which was vacuum infiltrated in the synthesized porous silicon and electrodeposited on the same with the standard three electrodes chronopotentiometry method, at a constant current density of about 2 mA/cm² for 120 seconds. Electrodeposited porous silicon was kept on the hot plate for 10 min at 220℃, followed by a thermal treatment at 600℃, for 180 min, in the presence of N2 flow (1 L/min).The surface morphology of the unpassivated porous silicon (UPSi) and passivated porous silicon (PPSi) are shown in the insets of Fig. 1(a) and (b), respectively. This suggests the presence of an incredibly thin coating of the polymer on the pore walls. The pores in, both, unpassivated and passivated porous silicon samples (UPSi and PPSi) remained open and unobstructed, offering a uniform distribution of pores with sizes ranging between 5 nm and 20 nm.To perform a corrosion test of the UPSi and PPSi, we look at these layers after they have been exposed to 1 M NaOH aqueous solution, for different time durations. We have seen the formation of a spontaneous bubble on the surface of the UPSi sample during the test. To this end, we have observed visible and morphological changes of both UPSi and PPSi samples after the corrosion stability test for 5 seconds and 120 minutes, respectively, as seen in Fig. 1(a) to (h). Due to the very high internal area and the hydrogen-terminated surface, in an aqueous solution, UPSi is oxidized by water at room temperature and degrades. In comparison, the PPSi sample is stable for more than 120 minutes.Electrochemical characterisation of UPSi and PPSi was performed in a 10 mM NaCl aqueous electrolyte with a three-electrode cyclic voltammetry (C-V) setup. C-V measurements of the UPSi sample show strong redox reaction in the potential window of 0 V to 1 V, whereas, the PPSi sample shows a nearly constant charging current response in the potential window of -1 V to 1 V, as shown in Fig. 1(i). These results emphasize that the passivation of porous silicon using 2,6 DHN polymer makes it more stable and less reactive in an aqueous medium. Figure 1

High-performance UV light detector using layered perovskites and textured silicon heterojunction

UV photodetectors have gained popularity due to their high precision and capability to filter out interference from solar electromagnetic radiation. A UV detector of (BA)2PbCl4/textured silicon (BA = n-butylammonium) heterojunction was fabricated by depositing (BA)2PbCl4 thin film on textured silicon. High performances of a rapid UV light response (trise = tfall = 0.24 s), high responsivity (8.16 mA/W), and a low detection limit (7.5 μW/cm2) were obtained from the designed detector, which were ascribed the unique morphology and structure of the detector. The rough surface morphology of textured silicon enlarges the light-absorbing area of (BA)2PbCl4 by 20 times. Moreover, a p-n junction was constructed between (BA)2PbCl4 and textured silicon. The electric field naturally present in the heterojunction facilitates the transport of carriers. Furthermore, the (BA)2PbCl4/textured silicon heterojunction exhibited significant selectivity towards UV light and demonstrated remarkable stability and repeatability in the air environment. This work offers a new strategy for developing inexpensive and high-performance UV photodetectors, which is significant for exploring the potential of layered perovskites in new photodetector device applications.

Optoelectronic properties of black silicon fabricated by femtosecond laser in ambient air: exploring a large parameter space.

We study the surface morphology, optical absorption (400-1100 nm), and carrier lifetime of black silicon fabricated by femtosecond (fs) laser in air. We explore a large laser parameter space, for which we adopt a single parameter ξ to describe the cumulative fluence delivered to the sample. We also study the laser-oxidized surface layer by measuring its photoluminescence spectra and comparing its effect on the aforementioned properties. Our study in a broad range of ξ is instructive in choosing laser parameters when targeting different applications.

Fabrication of Porous Silicon as a Gas Sensor: The Role of Porous Silicon Surface Morphology

Manufacture of an environmental polluting gas sensor with improved properties by controlling the preparation conditions of the photo-electrochemical etching technique (PECE). The amount of porosity, the diameter of the pores, and the thickness of the prepared layer of porous silicon (Psi) can be controlled by changing one or all of these conditions. In this paper, n-type Si with a crystalline orientation (100) was used, whereby PSi was prepared with the use of a red diode laser with a wavelength of 650 nm, using different radiation intensity, and with the constancy of etching time and current density. Through the results obtained, it was noted that: the porosity increases significantly up to 75% as well as the thickness of the PSi layer up to 1.45 µm with the increase in the intensity of the laser beam. Also, examining the morphology of the surface samples by field emission scanning electron microscope (FE-SEM) besides, the average pore diameters of the prepared samples were calculated. It is clear that the intensity of the laser beam used in the irradiation process is one of the important factors in determining the properties of the prepared PSi. PSi samples have been tested by FTIR to investigate chemical bonds on surfaces such as, (Si-Si, Si-H, Si-H2, Si-O-Si, Si-O-Si, Si-H, Si-O-Si). Samples tested as gas sensors and noticed that an increase in the sensing current to 5.3 µA has appeared with the increase of porosity value where methanol gas is used as background.

Surface Morphology Evolution during Chemical Mechanical Polishing Based on Microscale Material Removal Modeling for Monocrystalline Silicon.

Chemical–mechanical polishing (CMP) is widely adopted as a key bridge between fine rotation grinding and ion beam figuring in super-smooth monocrystalline silicon mirror manufacturing. However, controlling mid- to short-spatial-period errors during CMP is a challenge owing to the complex chemical–mechanical material removal process during surface morphology formation. In this study, the nature of chemical and mechanical material removal during CMP is theoretically studied based on a three-system elastic–plastic model and wet chemical etching behavior. The effect of the applied load, material properties, abrasive size distribution, and chemical reaction rate on the polishing surface morphology is evaluated. A microscale material removal model is established to numerically predict the silicon surface morphology and to explain the surface roughness evolution and the source of nanoscale intrinsic polishing scratches. The simulated surface morphology is consistent with the experimental results obtained by using the same polishing parameters tested by employing profilometry and atomic force microscopy. The PSD curve for both simulated surface and experimental results by profilometry and atomic force microscopy follows linear relation with double-logarithmic coordinates. This model can be used to adjust the polishing parameters for surface quality optimization, which facilitates CMP manufacturing.

Functional Performance of Silicon with Periodic Surface Structures Induced by Femtosecond Pulsed Laser

A micro/nano surface structure can produce specific properties, such as super hydrophilicity, low reflectance property, etc. A femtosecond laser-induced periodic surface structure is an important manufacturing process for the micro/nano structure. This research investigated the effects of scanning intervals and laser power on the surface morphology, wetting properties, and reflectance properties of LIPSS based on a silicon wafer. The results showed that the laser power had a significant effect on the surface morphology and wettability of silicon. With the increase of laser power, the surface roughness, etching depth and surface hydrophilicity increased. However, the laser power had little effect on the surface reflectance. The scanning interval had a great influence on the wettability and reflectance property of silicon. With the decrease of the scanning interval, the surface hydrophobicity and reflectance of silicon first decrease and then remain basically stable from 10 μm.

Prediction and verification of wafer surface morphology in ultrasonic vibration assisted wire saw (UAWS) slicing single crystal silicon based on mixed material removal mode

Monocrystalline silicon slicing is the first step in making chips, and the surface quality of silicon wafers directly affects the quality of later processing and accounts for a large proportion in the chip manufacturing cost. Ultrasonic vibration assisted wire saw (UAWS) is an effective sawing process for cutting hard and brittle materials such as monocrystalline Si, which can significantly improve the surface quality of silicon wafers. In order to further study the formation mechanism of the surface morphology of single crystal silicon sliced by UAWS, a new model for prediction of wafer surface morphology in UAWS slicing single crystal silicon based on mixed material removal mode is presented and verified by experiments in this paper. Firstly, the surface model of diamond wire saw tool is established by equal probability method. Then, the trajectory equation of arbitrary abrasive particles on the surface of wire saw is derived and analyzed. Thirdly, a new model for prediction of the wafer surface morphology based on mixed material removal mode is presented. Finally, the prediction model is verified by UAWS slicing experiment, and the effects of slicing parameters such as wire saw speed, feed speed, and workpiece rotate speed on the surface quality of silicon wafer were studied. It shows that the predicted wafer surface morphology and the experimental wafer surface morphology are similar in some characteristics, and the average error between the experimental and the theoretical values of the wafer surface roughness is 11.9%, which verifies the validity of the prediction model.

Laser desorption/ionization on nanostructured silicon: morphology matters.

The surface morphology of the silicon nanostructure plays a crucial role in the laser desorption/ionization (LDI) process. Understanding the correlation between the surface morphology and LDI performance is the foundation for creating silicon substrates with high LDI efficiency. Most of the present studies focus only on the structural parameters (such as porosity, depth, total surface area, dimension, etc.) of a single structure, but their effects on LDI efficiency vary with the types of silicon structures. Herein, two representative types of silicon nanostructures, porous silicon (PSi) and thorny silicon (TSi), were created to address this issue. The results indicate that the PSi substrate can generate a stronger heat effect and is beneficial to desorption; the TSi substrate can facilitate electron transfer and is favorable to ionization. Subsequently, the assertion was further confirmed by simultaneously detecting a dozen of standard samples and a real sample on both the TSi and PSi substrates, in which PSi can significantly enhance the detection signals of organic salts, whereas the TSi substrate can greatly increase the LDI efficiencies of neutral analytes. This finding provides a foundation for improving the LDI performance by tailoring silicon nanostructures, which is helpful for designing and creating substrates with high LDI performance.

Study for Laser Controlled Fabrication of Micro/Nano-Structures of Silicon Based on Multi-Physics Model.

This work proposes a detailed process of micro/nano-structure surface modification in relation to temperature field. In this paper, a femtosecond laser is used to induce the surface morphology of a silicon substrate. We provide a new method for the fabrication of a micro/nano-cantilever probe by controlling the aspect ratio of the silicon surface morphology. A computational method is used to investigate the mechanical behaviors of early perturbation to late-stage structure. A diffuse interface model is employed to describe the evolution and provide a general framework. The theoretical model of femtosecond laser control surface morphology is verified by the experiments. For systematic study, the model involves the interface energy and kinetics of diffusion. This method provides an effective way to improve the sensitivity of micro/nano-cantilever sensors.

Synthesis Of High Silicon Zeolites From Kaolin And Bentonite

In this paper problems of chemical and physical activation of local raw materials caoline and bentonite, and textural characteristics of high silicon zeolites and surface morphology were studied. The effect of the activation method of caoline and bentonite on the colloidal and sorption capacity was also studied. During the studies, the heat of wetting, adsorption linked water content and effective relative surface area were determined. Calculated distribution of pores by cycles (loops) of isothermal hysteresis r ≈ 8.5 nm. The volume of porosity of the sorbent when the capillaries were filled with water was determined as Vn= 0.135 cm3/g.

Degradation study of carrier selective contact silicon solar cells with ageing: Role of silicon surface morphology

Ageing effect on the performance of Ag/ITO/MoOx/n-Si/LiFx/Al carrier selective contact (CSC) silicon solar cells has been investigated based on silicon surface morphology (planar, different pyramid sizes, and chemical polishing of pyramids). The cells with small silicon pyramids (~2 µm) have shown better stability with time than the medium/large pyramids (~5/~8 µm). The chemical polishing of pyramid peaks and valleys has further reduced the cells ageing effect due to minimization of the microstructural stress (tensile in the valleys and compressive at the peaks) at the MoOx/n-Si interface, which has been verified indirectly with cells fabricated on a planar surface. The cell’s performance degradation based on morphology points out the instability of the MoOx layer and Schottky barrier reduction, which results in hole-transport hindrance at the MoOx/n-Si junction with the S-shape in J-V graphs under illumination. The ageing effect on device performance is further investigated using the Sentaurus TCAD simulations with the MoOx layer work function variation, and the study indicates the band bending reduction (minimal carrier inversion) and hole transport barrier at the junction region.

An Experimental Study on Irradiated Interface of Silicon

Atomic Force Microscopic (AFM) studies of Mega electron-volt (MeV) ions irradiated silicon surface morphology has been studied to a fluence of 5 x 108 ions/cm2. Interesting features of cracks of 50 nm in depth and 100 nm in width have been observed on the irradiated surface. The features seemed to have been caused by the irradiation-induced stress in the irradiated regions of the target surface. The observed feature of crack seems to be mainly due to the high electronic energy loss of the irradiated ions on the surface that induces the stress in it. It confirms that the coarseness of the microstructure of a material directly affect the mechanical properties.

Preparation and characterization of NiO/PSi as self-cleaning surface

Water-resistant surfaces are very important to many modern technology applications. So the progresses of hydrophobic & hydrophilic surfaces for self-cleaning applications has received widespread attention over the past years. In this paper, investigating in self-cleaning surfaces technique are presented. Nickel oxide Nanoparticles (NiONPs) were manufactured at different concentrations on the porous silicon (PSi) surface by immersion plating process, which filled with square-pores like structure which affected in classification of hydrophilic and hydrophobic surfaces. This green method to prepare Nickel oxide Nanoparticles/porous silicon (NiONPs/PSi) structures was interesting because it is effective for self-cleaning applications and is low cost and environmentally friendly. NiONPs/PSi structures characterized by the use of X-Ray Diffraction, electron microscopy scanning, Fourier-transform infrared (FTIR) analysis, Ultraviolet–visible (UV) spectroscopy, and contact angle analysis. The results show that hydrophilicity & hydrophobicity of these structures strongly depend on the surface morphology of porous silicon and the resulting the shape and distribution of NiO nanoparticles. From all results, it was found that the optimum contact angle is 118° at a NiO concentration of 10-2 M for the NiONPs/PSi structure which has hydrophobic properties as it can be used as a self-cleaning surface.

Analysis of Surface Morphology and Chemical Composition of Silicon Implanted with Copper Ions

We report on the results of analysis of the structure and chemical composition of the surface of c-Si single crystal substrates implanted with Cu+ ions with energy of 40 keV and doses in a range of 3.1 × 1015–1.25 × 1017 ions/cm2 for a current density of 8 μA/cm2 in the ion beam. It has been established using scanning electron microscopy and probe microscopy combined with X-ray photoelectron and Auger spectroscopy that at the initial stage, the implantation with Cu+ ions to a dose of 6.25 × 1016 ions/cm2 induces the formation of Cu nanoparticles with an average size of 10 nm in the Si surface layer. Upon a further increase in the implantation dose, beginning with 1.25 × 1017 ions/cm2 and higher, the nucleation of the η phase of copper silicide (η-Cu3Si) is observed. This is due to heating of the surface layer of the Si substrate during its irradiation to a temperature facilitating the formation of the η-Cu3Si phase.

Cavity resonance tunability of porous silicon microcavities by Ar+ ion irradiation

Present work reports the effect of low-energy Ar+ ion beam irradiation on the optical properties and surface morphology of porous silicon (PSi) based optical microcavities. These microcavities were realized by an active λ/2 spacer layer sandwiched between two Distributed Bragg Reflectors fabricated by galvanostatic electrochemical etching. Low-energy 10 keV Ar+ ions at various fluences were used for this irradiation study for these microcavities and characterized. The peak in the reflectance spectra of resonant cavity shows a red-shift after ion irradiation. These experimental observations are in good agreement with transfer matrix simulations. The Raman studies show that the crystalline Si is modified in nanostructured PSi and subsequently, the structural features of Si-Si and Si-O bonds. The simulated depth profiles suggest that the penetration of Ar+ ion is limited to top two PSi layers and the reduction of effective refractive index of these two layers. These experimental findings, analytical simulations, and cavity modelling provide the evidence of resonent cavity peak tunability, optical field intensity modulation, and photon confinement within the microcavity. This approach could be useful to tune the optical properties of PSi and an effective method for producing widely tunable optical structures in Si-based photonic architectures.

Properties investigation of crystalline silicon surface irradiated by nanosecond laser pulses in different background atmospheres

Black silicon materials were obtained by irradiation with ns laser pulses in different ambient atmospheres. The surface morphology, optical properties, and electrical properties of the black silicon were investigated after the ablation by ns laser pulses. Slab-like structures and boundaries were formed on the surface of black silicon fabricated in sulfur hexafluoride (SF6), argon (Ar), and vacuum. In addition, a micrometer-sized sphere was observed at the tip of the slab-like structure, which was not obvious for the black silicon prepared in oxygen (O2), nitrogen (N2), and air. The infrared absorption of all the black silicon materials was enhanced. For the two samples fabricated in SF6 and Ar, the infrared absorptance was approximately 50% at 1500 nm. A post-thermal annealing process decreased the infrared absorptance of all the black silicon materials except for that prepared in SF6. The sheet resistance of the black silicon was reduced by the ns laser irradiation process, and thermal annealing further decreased the sheet resistance of all the samples except for the one fabricated in SF6. After annealing at 875 K, the sheet carrier density of the black silicon fabricated in an Ar atmosphere and vacuum was approximately 1013 cm−2, which was approximately three orders of magnitude larger than that of the silicon substrate (1010 cm−2). The large difference in carrier density between the black silicon layer and substrate is beneficial for establishing contact junctions and for application in infrared photodetection.

3D characterisation using plasma FIB-SEM: A large-area tomography technique for complex surfaces like black silicon

This paper demonstrates an improved method to accurately extract the surface morphology of black silicon (BSi). The method is based on an automated Xe+ plasma focused ion beam (PFIB) and scanning electron microscope (SEM) tomography technique. A comprehensive new sample preparation method is described and shown to minimize the PFIB artifacts induced by both the top surface sample-PFIB interaction and the non-uniform material density. An optimized post-image processing procedure is also described that ensures the accuracy of the reconstructed 3D surface model. The application of these new methods is demonstrated by applying them to extract the surface topography of BSi formed by reactive ion etching (RIE) consisting of 2 µm tall needles. An area of 320 µm2 is investigated with a controlled slice thickness of 10 nm. The reconstructed 3D model allows the extraction of critical roughness characteristics, such as height distribution, correlation length, and surface enhancement ratio. Furthermore, it is demonstrated that the particular surface studied contains regions in which under-etching has resulted in overhanging structures, which would not have been identified with other surface topography techniques. Such overhanging structures can be present in a broad range of BSi surfaces, including BSi surfaces formed by RIE and metal catalyst chemical etching (MCCE). Without proper measurement, the un-detected overhangs would result in the underestimation of many critical surface characteristics, such as absolute surface area, electrochemical reactivity and light-trapping.

Modelling of single UV nanosecond pulsed laser surface modifications of silicon

Irradiation with a single spatially Gaussian-shaped nanosecond laser pulse in the melting regime can result in a characteristic annular change in the surface morphology of crystalline silicon. This has been verified experimentally in a variety of situations, where dimple-shaped surface topographies are produced. In a recent work we have investigated the induced changes in the surface topography upon exposure to wavelengths in the visible and near infrared spectral region. Irradiation in the UV requires a more detailed analysis due to the enhanced absorption of the material. In the present analysis, we determine under which conditions our previous model can be used and the corresponding results are presented.

Formation of periodic superhydrophilic microstructures by infrared nanosecond laser processing of single-crystal silicon

The evolution of the morphology and composition of the single-crystal silicon surface irradiated by infrared and visible nanosecond laser pulses is investigated as a function of processing parameters (laser fluence, irradiation spot size, the number of pulses, background gas pressure and composition). Two types of periodic surface microstructures are obtained with IR (1064 nm) laser pulses in a narrow fluence range of 3–6 J/cm2. At a relatively low number of laser pulses applied, a grid of cleavage cracks is produced within the irradiation spot along the crystal orientation. With further Si irradiation, periodic microhillocks are formed in the nodes of the crack grid. Silicon surface with such microhillocks exhibits superhydrophilic properties which are retained during prolonged storage in air. The cracks are produced in any environment (including vacuum) but the microhillocks are observed only in the presence of oxygen. No periodic structures were observed with visible (532 nm) laser pulses. Mechanisms of nanosecond laser-induced periodic microstructure formation on silicon are discussed.