Monocrystalline Silicon Substrates Research Articles

Enhanced optoelectronic performance of plasma electrolytic oxidized monocrystalline silicon using rGO incorporation

rGO/SiO2 composite coating was successfully prepared by plasma electrolyte oxidation (PEO) process on monocrystalline silicon (mc-Si) substrate. Investigating the effect of rGO incorporation into the SiO2 coating revealed that the addition of rGO leads to a significant increase in the photo-trapping ability due to the high specific surface area and excellent electron transfer efficiency. The PL intensity of the composite sample was found to decrease, which signified the suspension of the electron-hole pairs’ recombination. As a result, the photocurrent gain of the composite coating enhanced about 5.5 times. Likewise, the time-response switching featured an over two-fold increase for the rGO/SiO2 coating, impressively.

Photoacoustic characterization of nanowire arrays formed by metal-assisted chemical etching of crystalline silicon substrates with different doping level

Silicon nanowire (SiNW) arrays were investigated by gas-microphone photoacoustic (PA) technique to evaluate the thermal conductivity and optical absorption. The arrays with SiNW's length from 3 to 25 μm were formed by metal-assisted chemical etching of (100)-oriented monocrystalline silicon (c-Si) substrates with the low and high concentration of doping impurities. PA responses of SiNWs were excited by sources with wavelengths of 460 and 630 nm in the frequency range from 15 to 1150 Hz. An analysis of the experimental data reveals that the thermal conductivities of SiNWs formed on the lightly and heavily doped substrates are about 4–7 and 0.17–0.22 W/(m K), respectively. The latter value is explained by the porous structure of the SiNWs, promoting a strong restriction of the phonon free path. The thermal conductivity and optical absorption of SiNW arrays depend on the doping level and length of SiNWs due to a combination of the phonon and light scattering processes.

Light harvesting and effective surface passivation using electrodeposited Y2O3 for broadband absorption enhancement in silicon solar cells

This paper reports investigation on passivation properties of electrodeposited yttrium oxide Y2O3 thin films on monocrystalline silicon substrate. We examined its application as an effective light harvesting and a passivation layer to enhance the electrical properties of the processed solar cell. We found that the deposited Y2O3 thin film is excellent antireflection coating and post deposition sintering acts to passivate the coated monocrystalline silicon substrate. Next, the coated substrates were annealed at various temperatures for a short duration. The crystallinity of the deposited yttrium oxide thin film was analyzed by means of X-ray diffraction. The latter shows an obvious dependence with the annealing temperature. Surface morphology was examined by a field emission scanning electron microscope and revealed a high tendency for light scattering through its particular morphology, essentially after post-annealing at 650 °C. The effective minority carrier lifetime measurements, using a WTC-120 photoconductance lifetime tester, show an obvious increase indicating the vital role of yttrium oxide on the passivation of the front surface. The electrical properties were studied using the Hall effect and the Van Der Pauw methods to measure the resistivity and mobility of the majority carriers. The effect of the deposited thin film on the optoelectronic properties was evaluated by means of the internal quantum efficiency that was improved noticeably, proving a large decrease of the recombination activities mainly at the front surface. These results show clearly that the deposited layer has a double effect: a passivating layer and an antireflective layer increasing the light trapping at the front side of the processed silicon solar cell.

Influences of Bath Chemistry and Plating Variables on Characteristics of Electroless Ni–P Films on Si Wafers from Alkaline Citrate Solutions

Electroless nickel–phosphorus (Ni–P) films were produced on the surface of p-type monocrystalline silicon in the alkaline citrate solutions. The influences of bath chemistry and plating variables on the chemical composition, deposition rate, morphology, and thermal stability of electroless Ni–P films on silicon wafers were studied. The as-deposited Ni–P films were almost all medium- and high-P deposits. The concentrations of Ni2+ and citric ions influenced the deposition rate of the films but did not affect P content in the deposits. With increasing H2PO2− content, the P content and deposition rate were steadily increased. The pH and plating temperature had a significant effect on the chemical composition and the deposition rate of the films. The thermal stability of the medium-P film was better than that of the high-P deposit. At the same time, the proposed mechanism of Ni–P films on monocrystalline silicon substrates in the alkaline bath solution was discussed and addressed.

Nanoindentation of ZrN Coatings on Silicon and Copper Substrates

An effective mathematical model is proposed to describe experiments on the indentation of samples with layered or functionally graded coatings. The model is based on the elastic contact problem corresponding to the penetration of a punch in a coated elastic half-space. A Berkovich indenter is considered. The results of the simulation and the experiments are compared for the indentation of two zirconium nitride (ZrN) coatings on substrates of monocrystalline (100) silicon and annealed copper. The agreement of the results is good.

Nucleation and sliding growth of boiling bubbles on locally heated silicon surfaces

In this work, nucleate pool boiling is investigated experimentally on smooth monocrystalline silicon substrates with or without cavities. Different from the previous studies, the substrates are locally heated by an H-shaped titanium thin-film heater deposited on the back surface of the substrate. High-speed infrared thermography (HSIR) synchronized with high-speed video (HSV) is used to measure wall temperature evolutions and record bubble dynamic behaviors. On the basis of HSIR images, the variation of bubble locations on the wall is precisely located. The results show that the boundary of heater changes bubble dynamics significantly. For the first time, a very interesting bubble sliding from the nucleation site to the heater boundary is observed on the substrates with or without cavities. However, this phenomenon was never observed on infinitely larger heated substrates. The transient evolutions of wall temperature indicate that an asymmetric temperature profile occurs beneath the bubble due to bubble sliding. The asymmetric temperature profile is used to distinguish the sizes of microlayer and macrolayer. Finally, a simple model is proposed to explain the sliding mechanism.

Influence of por-Si sublayer on the features of heteroepitaxial growth and physical properties of InxGa1-xN/Si(111) heterostructures with nanocolumn morphology of thin film

Integrated heterostructures with a nanocolumn morphology of the film InxGa1-xN were grown using the method of molecular beam epitaxy, with plasm activation of nitrogen on a monocrystalline silicon substrate с-Si(111) and c-Si(111) substrate with a nanoporous buffer sublayer (por-Si).By means of a complex of structural and spectroscopy analysis methods, it was shown that the growth of InxGa1-xN nanocolumns on a nanoporous buffer substrate has numerous advantages compared to when c-Si is used. The por-Si substrate largely contributes to the orientation of the growth of the InxGa1-xN nanocolumns closer to that of Si(111), allowing the InxGa1-xN nanocolumns to be obtained with a higher crystallographic uniformity and a unified lateral size along the entire surface of ∼40 nm. In addition, the growth of the InxGa1-xN columns on por-Si results in a decrease in the deformation component εxx and εzz, as well as the density of edge and screw dislocations compared to similar coefficients for the InxGa1-xN nanocolumns grown on c-Si. Furthermore, the nanocolumn InxGa1-xN obtained using por-Si substrate has a higher carrier charge concentration (+20%) compared to that grown using c-Si, as well as a higher intensity of a quantum yield of photoluminescence (+25%).

Texturization of as-cut p-type monocrystalline silicon wafer using different wet chemical solutions

Implementing texturization process on the monocrystalline silicon substrate reduces reflection and enhances light absorption of the substrate. Thus texturization is one of the key elements to increase the efficiency of solar cell. Considering as-cut monocrystalline silicon wafer as base substrate, in this work different concentrations of Na2CO3 and NaHCO3 solution, KOH–IPA (isopropyl alcohol) solution and tetramethylammonium hydroxide solution with different time intervals have been investigated for texturization process. Furthermore, saw damage removal process was conducted with 10% NaOH solution, 20 wt% KOH–13.33 wt% IPA solution and HF/nitric/acetic acid solution. The surface morphology of saw damage, saw damage removed surface and textured wafer were observed using optical microscope and field emission scanning electron microscopy. Texturization causes pyramidal micro structures on the surface of (100) oriented monocrystalline silicon wafer. The height of the pyramid on the silicon surface varies from 1.5 to 3.2 µm and the inclined planes of the pyramids are acute angle. Contact angle value indicates that the textured wafer’s surface fall in between near-hydrophobic to hydrophobic range. With respect to base material absolute reflectance 1.049–0.75% within 250–800 nm wavelength region, 0.1–0.026% has been achieved within the same wavelength region when textured with 0.76 wt% KOH–4 wt% IPA solution for 20 min. Furthermore, an alternative route of using 1 wt% Na2CO3–0.2 wt% NaHCO3 solution for 50 min has been exploited in the texturization process.

Thermodynamic energy variation diagram to speculate preferred growth orientation of magnetron sputtered PbSe thin films on monocrystalline silicon substrates

The optical and photoelectric properties of lead selenide (PbSe) thin films are intensively affected by the thin film crystal structure which is mainly determined by the growth process. In this paper, the growth mechanisms of the magnetron sputtered PbSe thin films on two different monocrystalline silicon substrates (Si(100) and Si(111)) were thermodynamically simulated and experimentally confirmed. The results showed that the growth process of PbSe thin films is mainly affected by the minimization of the interface and strain energy along [200] and [220] crystal orientations, while the surface energy contribution can be neglected. Specifically, the PbSe thin film with [200] and [220] preferred orientation is obtained when the interface and strain energy minimization dominates the growth process, respectively. According to the calculated thermodynamic energy variation diagram, the probability of PbSe thin film grows along [200] orientation on Si(100) substrate is higher than on Si(111), while the probability for [220] orientation is opposite, indicating that the properties of the sputtered PbSe thin films can be preciously speculated and modified on the basis of the thermodynamic calculations.

Determination of refractive index and thickness of YbF3 thin films deposited at different bias voltages of APS ion source from spectrophotometric methods

Abstract Ytterbium fluoride (YbF3) single thin films were prepared on sapphire and monocrystalline silicon substrates through conventional thermal evaporation and ion beam-assisted deposition (IAD), at bias voltages ranging from 50 to 160 V of the Leybold advanced plasma source (APS). By using the Cauchy dispersion model, the refractive index and thickness of the YbF3 thin films were obtained by fitting the 400–2500 nm transmittance of the monolayer YbF3 thin films on the sapphire substrate. At the same time, the refractive index and thickness of the YbF3 thin films on the monocrystalline silicon substrates were also measured using the VASE ellipsometer at wavelength from 400 to 2200 nm. The results showed that the refractive index deviation of the YbF3 thin films between the fitted values by the transmittance spectra and the measured values by the VASE ellipsometer was <0.02 and the relative deviation of the thickness was <1%. Furthermore, the refractive index of the YbF3 thin films increased with increasing APS bias voltage. The conventional YbF3 thin films and the IAD thin films deposited at low bias voltage revealed a negative inhomogeneity, and a higher bias voltage is beneficial for improving the homogeneity of YbF3 thin films.

Investigating the effect of silicon surface chemical treatment on Al/Si contact properties in GaP/Si solar cells

In the present work, experimental studies have been carried out to reveal how chemical treatment of a silicon surface affects the properties of the Al/Si contact. It has been shown that for p-type monocrystalline silicon substrates with a resistivity of 10 ohm cm, it is possible to form an ohmic Al/Si contact by magnetron sputtering of an aluminum thin film and its further annealing at temperatures of 400 - 450 °C. In the range of annealing temperatures of 250 - 400 °C, the Si substrate treatment in the HF solution leads to a significant increase in currents on the current-voltage curves of the Al/Si contact, while in the range of 450 - 700 °C, the effect of chemical treatment of the silicon is not detected.

Yttrium oxide passivation of porous silicon nanostructures for improved photoluminescence and optoelectronic properties

This paper reports on the effect of yttrium oxide as a novel treatment to improve the photoluminescence (PL) intensity and stability of porous silicon (PS). Yttrium oxide (Y2O3) was incorporated into the PS layers by impregnation method using a saturated aqueous solution. The penetration of yttrium into the PS microstructure was examined using the Energy dispersive X-ray spectrometry (EDS) and the backscattered electron detector (BED-C) for composition imaging and analysis. The morphology of the front surface was studied using a field emission scanning electron microscope. The deposited yttrium oxide onto the PS layers was thermally activated to passivate efficiently the silicon dangling bonds, and prevent the PS from huge oxidation. The PL peak intensity of impregnated PS was increased noticeably compared to the as-prepared untreated PS. Unlike the as-prepared PS photoluminescence dependence with aging, the yttrium-passivated PS layers PL peak shows no shifts during aging allowing a high stability. Furthermore, we obtained a significant improvement of the effective minority carrier lifetime (τeff) after a short anneal at 600 °C, while increasing the temperature reduces noticeably the passivation properties. The improved surface passivation experienced after the thermal annealing can be ascribed to yttrium diffusion into the PS layer, with a resulting redistribution of yttrium oxide and subsequent passivation of silicon dangling bonds in the sub-interface region, this was confirmed by EDS analysis. The internal quantum efficiency measurements were performed to study the optoelectronic properties of the processed monocrystalline silicon substrates.

Parameter Calculation and Investigation of a MIS Varicap with Charge Transfer for L-Range Microwave Devices

The characteristics of a MIS varicap with charge transfer designed for control microwave devices are analyzed. The limiting frequency of the device is shown to be at least twice as high as that of the standard MIS varicap based on a MIS system with a thicker dielectric in the varicap with charge transfer. A method for parameter measurements in the microwave range is developed. Some device samples are fabricated based on thin substrates of monocrystalline silicon with epitaxial layers. The correspondence between the theoretical and experimental characteristics of the varicap is established.

Properties of Nanocomposite Nickel-Carbon Films Deposited by Magnetron Sputtering

The method of magnetron sputtering was used to produce a-C and a-C:Ni films on substrates of monocrystalline silicon and thermoelectric material of n-type ((Bi2Te3)0.94(Bi2Se3)0.06) and p-type ((Bi2Te3)0.20(Sb2Te3)0.80) conductivity. The authors studied the effect of Ni concentration on specific electric resistance, hardness and adhesion of the produced films. It was demonstrated that specific resistance of a-C films deposited by graphite target sputtering when supplying high bias voltage onto the substrate can be reduced by increasing the share of graphitized carbon. Adding Ni to such films allows additionally reducing their specific resistance. The increase in Ni content is accompanied with the decrease in hardness and adhesion of a-C:Ni films. The acquired values of specific electric resistance and adhesion of a-C:Ni films to thermoelectric materials allow using them as barrier anti-diffusion coatings of thermoelectric modules.

Residual stress gradient of Cr and CrN thin films

In this work Cr, CrN thin films were grown by the Magnetron Sputtering technique on monocrystalline silicon (400) substrates. Also, a (Cr/CrN)2 multilayer film was grown in order to compare the values of stress between multilayer and single layers. The total thickness of all films was approximately equal to 1 μm. Structural characterization and residual stress measurements were performed by the grazing X-ray diffraction method and the data were collected at LNLS - Brazilian Synchrotron Light Laboratory. Different angles of incidence were selected in order to obtain values of residual stress at different penetration depths. A linear model of residual stress as a function of the depth profile from experimental data was obtained by using the Laplace transform. Results indicate smaller tensile residual stress at surface and higher stresses at film/substrate interface for the Cr monolayer and for the CrN phase in the (Cr/CrN)2 multilayer. On the contrary, the CrN film presented higher tensile stresses at surface.

Study on the influence of standoff distance on substrate damage under an abrasive water jet process by molecular dynamics simulation

The process of a cluster-containing water jet impinging on a monocrystalline silicon substrate was studied by molecular dynamics simulation. The results show that as the standoff distance increases, the jet will gradually diverge. As a result, the solidified water film between the cluster and the substrate becomes “thicker” and “looser”. The “thicker” and “looser” water film will then consume more input energy to achieve complete solidification, resulting in the stress region and the high-pressure region of the silicon substrate under small standoff distances to be significantly larger than those under large standoff distances. Therefore, the degree of damage sustained by the substrate will first experience a small change and then decrease quickly as the standoff distance increases. In summary, the occurrence and maintenance of complete solidification of the confined water film between the cluster and the substrate plays a decisive role in the level of damage formation on the silicon substrate. These findings are helpful for exploring the mechanism of an abrasive water jet.

Femtosecond pulsed laser deposition of nanostructured TiO2 films in atmosphere

Nanostructured TiO2 films were grown on a monocrystalline silicon substrate by a femtosecond pulsed laser ablating a Ti target in atmosphere without a vacuum chamber. FESEM and XPS results showed that the TiO2 nanomaterials prepared by this method have a fluffy structure composed of nanoparticles which have a particle size in the range of 1-100 nm, resulting in a high specific surface area of 88.6 m2/g. XRD results showed that the deposited films have a composited phase which is composed of anatase, rutile and amorphous TiO2. The reason for the formation of this nanostructure is mainly because of the collision with gas molecules and oxidation reaction of Ti ions. The method may be used to prepare other metal oxide nanostructured films.

Crystalline silicon growth on aluminum substrate for photovoltaic application

In this work, we investigate the direct formation of crystalline silicon thin films using ECR-PECVD process on aluminum substrates for solar cells applications. The aluminum substrate offers the advantages of being flexible and highly reflective in addition to serve as the back contact for the cell device. The substrates were pure aluminum or silicon rich aluminum sheets. Monocrystalline silicon substrates were used as reference substrates. Silane and hydrogen were used as precursor gases. Silicon growth was done at different substrate temperatures. The grown silicon films were characterized by Raman spectroscopy, SIMS and XRD techniques. Silicon thicknesses between 230 and 1370 nm were obtained on different types of aluminum substrates. The analyses show that the grown silicon films formed at 480 °C under SiH4: 40 sccm and H2 = 10 sccm are amorphous silicon at the initial stage and become nanocrystalline (nc-Si:H) as the deposition proceeds. The crystalline fraction of those films extracted from Raman spectra is found around 40–60% and XRD analysis shows grain silicon size between 41 and 83 A. Finally, SIMS analysis have revealed graded doping distribution profiles which is indicative of the formation of a nc-Si:H(i)/nc-Si:H (p+)/Al substrate, well suited for solar cell structures.

Antireflection TiO2 coatings on textured surface grown by HiPIMS

The aim of this work is to test the technology of the high impulse power magnetron sputtering (HiPIMS) for depositing TiO2 thin films on textured surfaces and to reveal anti-reflection properties of these films. Prior to deposition, the monocrystalline (100) silicon substrates were etched in KOH/IPA solution forming the surface texturization of the pyramidal structure. Thin films of different thicknesses were deposited by HiPIMS on silicon substrates using a titanium target in argon–oxygen atmosphere. In order to compare properties of different TiO2 structures, the additional textured samples were coated by conventional direct current (DC) method, as well. Anti-reflection coatings were characterized by spectrophotometry, ellipsometry, scanning electron microscopy, grazing incidence X-ray diffraction and transmission electron microscopy techniques. The HiPIMS deposited films were found to be characterized by the higher refractive index. These films appeared to be smooth, while uniformly covering the surface of the sample, including the space between pyramids. Moreover, the HiPIMS deposited films show the lowest reflectance in comparison to the DC deposited samples of the same thickness.

Study on ablation products of zinc by intense pulsed ion beam irradiation

AbstractAs a kind of flash heat source, intense pulsed ion beam (IPIB) can be used for material surface modification. The ablation effect has important influence on interaction between IPIB and material. Therefore, the understanding of ablation mechanism is of great significance to IPIB application. In this work, pure zinc targets were irradiated and ablated by IPIB. In the ablation process under the different ion beam energy densities, the ablation products were collected by a monocrystalline silicon substrate. By analyzing the ablation products with scanning electron microscope and energy-dispersive spectrometer, the surface morphology, and the spatial distribution of ablation products quantity were obtained. The results are useful for clearing the ablation process and the influence of beam parameter on the ablation effect.