Silicon nitride (SiN) films are crucial in microelectronic and photonic devices, where their interface affects performance and reliability. In this study the effect of deposition temperature on the surface roughness of amorphous SiN, films on silicon (Si) substrates is investigated using our kinetic Monte Carlo algorithm (Silicon 15, 5209 (2023)). The low-pressure chemical vapor deposition process is mod-eled on a three-dimensional triangular lattice with disilane (Si2H6) and ammonia (NH3) as precursor sources. The nanoscopic events included in this work are the nanoparticle adsorption and the Si adatom migration. A new growth model is adopted to control the obtained surface morphologies, Le., size and density of amorphous Si clusters as well as film surface roughness. The deposition of Si and N atoms is carried out alternately to create a SiN compound characterized by small Si clusters and a rough surface. Both volume migration and surface migration are taken into account during the simulation, leading to the development of vacancies and pores. The formation of peaks and valleys is described by our kinetic Monte Carlo algorithm. Our analysis includes deposition simulations at temperature values ranging from 723 to 753 K, with a gas flow rate fixed at 0.3 and a deposition duration of 1 h. The surface roughness values of the deposited nanostructures are deduced from the simulation matrix. Numerical results indicate that an increase in process temperature leads to an increase in the size of Si clusters along with an increase in surface roughness. The deposition temperature largely determines whether the film surface is smooth or rough. This means that our growth model is able to accurately predict the evolution of the film nanostructure for a wide range of process conditions. The stoichiometry z (N/Si ratio) is determined based on all deposition parameters. The average distance between Si clusters is also calculated here. The acquired insights enable the refinement of thin film deposition simulation techniques, the improvement of surface morphology properties, and the support of the development of reliable SiN platforms for microelectronics and photonics.

In this article, an approach to a 2D model of homojunction poly-Si/c-Si solar cells is demonstrated, in which the effects of grain joints on the electrical properties of the solar cell are analyzed. Using the Silvaco TCAD program, we were able to create a model of a solar cell consisting of grains separated from each other by grain boundaries. The physical models of the grain boundaries were introduced onto polysilicon. Based on experimental parameters, the grains were designed with an average size ranging from 40 to 80 [nm]. The density of traps stats at the grain boundaries between 4 similar to 9.10(16)[1/cm(2)] at an energy level between 0.15 similar to 0.17[eV]. The results clearly show that the efficiency of solar cell composed of polysilicon do with large grains is very high, compared to solar cell composed of poly-silicon-do with small grains, which It allows a large number of charge carriers to pass well due to the direct relationship between the grains and the grain joints. "The larger the size of the grains, the lower the density of the grain joints, and thus the cell yield is greater."

A systematic methodology is developed for modeling and controlling the surface roughness in LPCVD SiNx film deposition. The deposition process is modeled via kinetic Monte Carlo (KMC) simulation on a three-dimensional triangular lattice using disilane (Si2H6) and ammonia (NH3) as precursor sources. New algorithmic modifications are considered in our simulations to create a SiN compound with small Si clusters and a rough surface. The nanoscopic events included in this study are particle adsorption and subsequent migration, leading to the development of vacancies and pores. Vacancies and pores are allowed inside the porous SiNx film to model film thickness and surface roughness. The roughness and thickness of the obtained nanostructures are calculated in terms of the gas flow ratio, and a new method is proposed. Simulation results illustrate the effectiveness of the proposed modeling and control approach in the context of the surface roughness under consideration. Since the simultaneous control of surface roughness and film thickness is carried out, the obtained surface height structures are regulated to desired values. The formation of peaks and valleys is defined in our KMC algorithm. The dependence of surface roughness and film thickness on silicon (Si) cluster size is studied. The simulations reveal the existence of a minimum surface roughness after increasing the gas flow ratio.

We propose through this work a correlation method leading to a determination of a semi-empirical relationship between optical and electrical properties in terms of refractive index and dark conductivity of doped silicon nanocrystals based on experimental data published in literature. First, an analytical model relating the conductivity and bandgap of doped silicon nanocrystals was derived. Using an empirical expression relating the refractive index to the bandgap energy, we correlated the electrical and optical parameters of N-type nanocrystalline silicon with a semi-empirical expression. The semi-empirical relationship was found to account correctly for the experimental results and yield a reasonably good agreement in an interval of the bandgap energy variation of N-type silicon nanocrystal films. The values of the fitting parameters were calculated for the N-type silicon nanocrystal films having their bandgap energy between 1. 7 eV and 2.2 eV.

This work studies the effect of carrier trapping and the recombination activity at the grain boundaries in the p-layer of polysilicon solar cells with respect to the deposition temperature. The dependence of the grain size on the deposition temperature was studied in different samples of boron-doped low-pressure chemical vapor deposition (LPCVD) silicon deposits, conducted in a horizontal low-pressure atmospheric pressure reactor where the temperature varied over a range from 520 °C to about 605 °C. The obtained results show clear evidence of dependence on effective changes in the trapping effect as a function of the trapping density states, the doping level and the thickness dimension of the deposited layer.

In this work we will investigate the size distribution of the amorphous silicon quantum dots (Si-AQD) inside a silicon nitride film SiNx (x = 0.12). The studied film contains an ensemble of silicon nanocrystals (Si-nc) inside an amorphous silicon nitride matrix SiNy (y = 0.66). Since the nitrogen atoms number are less than the silicon atoms number in the amorphous matrix, we can suggest that silicon atoms can aggregate under amorphous quantum dots. In this context, we will first estimate the number of crystallized silicon atoms (c-Si). The number of amorphous silicon atoms (a-Si) can be deduced from the fraction of crystallized silicon atoms and leads to the determination of the number of nitrogen atoms. Results show that all the nitrogen atoms are localized in the Si-ncs cap shell. Thus, the amorphous quantum dots can be easily revealed from the scattering electron microscopy (SEM) image. The low yield of luminescence from amorphous quantum dots can explain the difference between both experimental and simulated photoluminescence (PL) from silicon nitride film containing Si-ncs.

In this study, we experimentally investigate the evolution of the Raman spectrum of single, bi-and trilayer graphene as function of gate voltage induced doping. In single layer graphene, the observed results are in agreement with the literature. Whereas, for bi-and tri-layer graphene, we report new results on the gate voltage induced doping dependence of G and 2D bands position, the 2D to G band intensity ratio and the G band linewidth. The gate bias through 90 nm-thick oxide allows us to move the Fermi level up to 0.43 eV and 0.31 eV for bi- and tri-layer graphene, respectively. We observe one minima in the evolution of the G band position of bilayer as function of doping. This result is explained by the presence of a larger charge density non-uniformity, which yields to electron and hole puddles in the sample. The G band position and linewidth and the 2D to G band intensity ratio show a slow variation with doping near the neutrality point, this becomes more important as doping keeps rising such as the trends present a parabolic shape dependence. We assign this to the band structure of bi- and tri-layer graphene where the carriers are massive with respect to single layer graphene. (C) 2019 Elsevier Ltd. All rights reserved.

Porous silicon (PS) has been prepared from n-type (100) silicon substrate by using electrochemical etching under He-Ne laser illumination. The PS was produced within several etching conditions. The morphological, structural and optical properties were studied by using atomic force microscopy (AFM), X-ray diffraction (XRD), Raman analysis, and reflectance measurements. Results show that the evolution of the obtained nanostructures is strongly related to anodization conditions. The optical analysis results show that a low reflectance was obtained for samples anodized by increasing current density. This is correlated to morphological results showing the strong dependence of the obtained nanoporous structure in terms of crystallites sizes and porosity, on the anodization conditions.

In this work, we have proposed a theoretical model allowing the calculation of electroluminescence (EL) from a light-emitting device, taken from the literature, composed of a silicon nitride film (containing silicon nanocrystals (Si-ncs)) between an indium thin oxide (ITO) layer and an aluminum (Al) anode. The EL model suggests that following the application of an electric field, carriers are injected by the Fowler-Nordheim process. The carriers transporting process to the cathode is modeled by the Hopping conduction and causing the generation of other carriers inside Si-ncs by ionic impact. The EL is created by the recombination of the carriers inside Si-ncs. Results exhibit that selective size distribution centered at a Si-nc radius of less than 1 nm allows blue emission for thin active film. The optimal carrier injection is obtained for bias voltages lower than 27 V that allowed the potential barrier diminution. A comparison between the experimental and the theoretical results indicated that the present model is able to satisfactorily explain the highest observed EL peak. (C) 2018 Elsevier GmbH. All rights reserved.

In this work, we will study the elastic and inelastic light scattering by the silicon nanocrystals (Si-nc) embedded in amorphous silicon nitride matrix. Indeed, the photons are subjected to several modifications in terms of intensity, direction and wavelength when they interact with Si-ncs. The reflectance combined with photoluminescence (PL) and Raman spectroscopy are a very sensitive tool for probing the scattering light. Results show that the observed shift of the experimental PL peaks is attributed to the Raman scattering and the PL broadening peaks to the Rayleigh scattering. A novel method allowed the determination of both the core and the surface bond lengths of Si-nc was reported. The decrease of the Raman shift observed in structures containing Si-ncs is mainly due to the Si-nc curved surface, and it reflects the presence of silicon dangling bonds at the Si-nc interfaces.

The reflectance combined with photoluminescence (PL) and Raman spectroscopy are a very sensitive tool for probing silicon nanocrystals (Si-ncs) characterization. Indeed, the structure of a thin film SiNx (x=0.12) containing Si-ncs in terms of composition, Si-ncs size distribution and defects is studied. The elastic and inelastic light scattering by the silicon nanocrystals (Si-nc) embedded in amorphous silicon nitride matrix are also investigated in this work. Results shows that the PL spectrum can be deconvoluted into several peaks attributed to the quantum confinement effect, the surface effect and the photocarriers recombinaision between band tail states in the amorphous matrix. The PL peak broadening is attributed to the Rayleigh scattering and the PL peaks positions are affected by the Raman scattering. Here we offer also a new approach to describe the coordination of the silicon surface atoms. From a parameter called the ratio of surface bonding contribution in Raman red shifts, we demonstrated that the silicon surface atoms are hyper coordinated under a sp3d2 hybridization.

This paper presents an analytical model calculating the threshold voltage in nanocrystalline silicon (nc-Si) thin film transistors by considering a granular morphology of silicon nanocrystallites forming the channel and using the two-dimensional the Poisson equation. The numerical calculations demonstrate that, according to the quantum size effects on both dielectric constant and band gap, the threshold voltage values are strongly related to the silicon crystallites structure. To justify the validity of our model suitable for implementation in circuit simulators such as SPICE, the simulation results obtained are compared with the available research data and they shows a satisfactory match, thus, demonstrating the validity of our model.

In this work, we shed light on a theoretical study of photonic crystal (PhC) cavities on Gallium Nitride (GaN). Particularly, the photonic band gap (PBG), resonant wavelength and quality factor (Q) of designed PhC structures were studied. In fact, the PBG was calculated by the plane wave expansion (PWE) method and the normalized transmission spectra of suspended GaN-based PhC cavities were obtained using finite difference time domain (FDTD) method. Accordingly, the resonant mode of GaN-based PhC cavity was observed at ∼460nm wavelength. Furthermore, the optical confinement of the hexagonal cavity can be improved by adjusting the diameter and the distances of the adjacent holes along with the change of the cavity's type from the H0 to the L3. Indeed, the transmission spectrum of the cavity was found to be strongly modified by the increase in the size of the structure, in the shifted distance value and the number of the shifted holes as well as the decrease of the holes diameters surrounding the defect in addition with changing the type of the cavity in order to obtain a significantly narrow FWHM of 0.002 pm. To sum up, our simulation results were in accord with those obtained from OptiFDTD software.

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In this work, the effect of the high silicon nanocrystals density as well as the radiated waves interference on the photoluminescence (PL) spectrum of silicon nanocrystal (Si-nc) embedded in silicon nitride film is studied. The film is prepared using low pressure chemical vapor deposition (LPCVD) following by a high temperature annealing. It was found that for silicon nitride of a high silicon content sample, the interference effect based on only the thickness of the film is unable to satisfactory explain the distortion on the PL spectrum. Using Monte Carlo analysis, it was shown that the simulated and the experimental PL spectra accurately superpose when taking into account the contribution of the reflection from silicon nanocrystals as well as the distance traveled by the radiated waves.

In the present work, the phase matching type II conditions using birefringence for second harmonic generation (SHG) in negative uniaxial crystals were studied. A novel numerical method allowing the simultaneous and reliable calculations of the type II phase matching angle and temperature versus fundamentals wavelengths for SHG in Lithium Niobate (LiNbO3) was proposed. The angles and temperatures were determined for values less or equal to 5×10−6 of uncertainty. Indeed, SHG efficiency curves at fundamental frequency f=1.6 THz obtained for various error values highlighted the validity and accuracy of the calculations. The proposed method was also applied in the case of the type I phase matching SHG using both the same crystal and precision. A good agreement between the analytical and numerical results was obtained.

The photoluminescence (PL) from silicon nanocrystals (Si-ncs) embedded in an amorphous silicon nitride matrix was examined both experimentally and through theoretical simulations. The film was prepared using low-pressure chemical vapor deposition with subsequent high-temperature annealing. The experimental parameters required for the PL modeling were determined using Raman spectroscopy. A novel method to estimate the nitrogen content, which allowed the determination of both the Urbach energy and the Tauc gap, was reported. The luminescence could be attributed to different origins, namely, Si-ncs, amorphous silicon nanodots, nitrogen and silicon defects, and amorphous matrix. A comparison between the experimental results and the modeling indicated that the existing models are unable to satisfactorily explain the observed PL.

In the present study, the deposition process of SiNx thin films obtained by a low-pressure chemical vapor deposition technique with a mixture of disilane (Si2H6) and ammonia (NH3) was simulated by using the kinetic Monte Carlo method. A new pattern describing the distribution of ammonia molecules in the simulation matrix was proposed. The influences of the NH3/Si2H6 gas flow ratio and the deposition temperature on the obtained films structure in terms of silicon cluster size and density were analyzed. The simulation results indicate that an increase in the gas flow ratio leads to the deposition of amorphous silicon clusters characterized by small sizes. Nevertheless, an increase in the temperature values of the process provokes an enhancement in the silicon cluster size along with a decrease in their density.