Search

The importance of the IT industry is becoming more and more prominent as it gradually changes to a non-face-to-face society after the COVID-19, and the next-generation smart devices of 5G mobile communication, micro LEDs, and wearable devices are emerging as the leading of the IT industry. Along with the development of these devices, limitations and problems of the Anisotropic Conductive Adhesive Film (ACF) used as a connection material for Film on Film (FOF), Chip on Glass (COG), Chip on Film (COF), and Film on Glass (FOG) are emerging. [1-5]

The influence of substrate temperature on the microstructural behavior, optical, electrical properties and on the scattering mechanism of charge carriers were studied for the as-prepared radio-frequency (R-F) magnetron sputtered Cadmium Tin Oxide (Cd2SnO4) thin films. Films prepared at the substrate temperature of 300 °C were found to be polycrystalline in nature with preferential orientation along (3 1 1) plane. Well pronounced Moss–Burstein shift, in the transmittance spectra with dispersions in the optical band gap from 3.07 to 3.30 eV, was observed at substrate temperatures between 25 and 300 °C. Optical property of high visible transmittance was retained by the films. Analysis of the electrical properties on the prepared crystalline Cd2SnO4 films showed a calculated resistivity of 10−3–10−4 Ω cm, with n-type carrier density in the range of 1019–1020 cm−3 and the charge carrier mobility in the range of 63–30 cm2/V s. The effects of structural, compositional and optical properties on the scattering mechanism of charge carrier are elaborated and reported to be an experimental evidence for the theoretical predictions. The results revealed the essential DC electrical conduction behavior, which is ideal for the fabrication of Cd2SnO4-based CdS/CdTe thin film solar cells.

We have investigated surface passivation of n and p type silicon wafers, obtained by controlling silicon–hydrogen bonding and fixed charge densities with the use of hydrogenated SiNx films. The hydrogenated SiNx films were deposited by single PECVD at 13.56 MHz with SiH4/NH3 gas mixture. The hydrogenated SiNx films of refractive indices 2.55–1.92 and high optical band-gap (> 3.1 eV) were obtained by varying the hydrogenated SiNx film composition. The fixed charge densities, hydrogen-bonding and carrier lifetime performance in n and p type silicon wafer were analyzed. The highest fixed positive charge of 2.66 × 1012 (cm− 2) was for the hydrogenated SiNx film composition of 1.21. Fourier transform infrared spectroscopy measurement was carried out to evaluate the bonding concentration of Si–H and N–H. The minority carrier lifetimes of the hydrogenated SiNx passivated silicon wafers were up to 153 μs and 84 μs for p and n type, respectively. Mechanism of surface passivation depends on the type of silicon wafer. The higher Si–H bond density is the key point of n type passivation quality. The large fixed positive charge is used to measure p type passivation quality.

This study is devoted to the formation of high–low-level-doped selective emitter for crystalline silicon solar cells for photovoltaic application. We report here the formation of porous silicon under chemical reaction condition. The chemical mixture containing hydrofluoric and nitric acid, with de-ionized water, was used to make porous on the half of the silicon surface of size 125×125 cm. Porous and non-porous areas each share half of the whole silicon surface. H 3 PO 4 :methanol gives the best deposited layer with acceptable adherence and uniformity on the non-porous and porous areas of the silicon surface to get high- and low-level-doped regions. The volume concentration of H 3 PO 4 does not exceed 10% of the total volume emulsion. Phosphoric acid was used as an n-type doping source to make emitter for silicon solar cells. The measured emitter sheet resistances at the high- and low-level-doped regions were 30–35 and 97–474 Ω/□ respectively. A simple process for low- and high-level doping has been achieved by forming porous and porous-free silicon surface, in this study, which could be applied for solar cells selective emitter doping.

Tri-crystalline silicon (Tri-Si) is a promising candidate to reduce the cost of solar cells fabrication because it can be made by a low-cost, fast process with a better mechanical strength, and needs a thinner wafer. One of the key parameters in improving the efficiency of the Tri-Si solar cells is the reflectance, which can be lowered by etching methods. However, Tri-Si is a crystal compound consisting of three mutually tilted monocrystalline silicon grains. In all grains boundaries the surface is (1 1 0)-oriented. A standard surface texture of etched random pyramids using an anisotropic etchant, such as NaOH, is not achievable here. In this paper, for the first time, a novel texturing method has been attempted, which consisted of two steps—HF:HNO3:DI (2.5:2.5:5) etching was followed by exposure to the vapors to generate fine holes and an etching depth of 2.5 μm had been reached. A best result of 12.3% has been achieved for surface reflectance, which is about 10% lower than that using normal acidic texturing. Nanoporous structures were formed and the size of the porous structure varied from 5 to 10 nm. An antireflection coating of SiNx SLAR was used to optimize the reflectance. A fill factor of 0.78 has been reached with an efficiency of 16.2% in 12.5 cm×12.5 cm. This high efficiency is mainly due to an increased short-circuit current density of 34 mA/cm2.

We performed a comparative study of the electro-physical properties of heterostructures containing PECVD nanocrystalline silicon (nc-Si) and electro-chemically etched porous silicon (PS) layers over a wide range of thicknesses, in terms of their energy parameters. Based on the proposed analytical expressions and the experimental current–voltage and capacitance–voltage characteristics, we studied the characteristics of the surface states at the nc-Si(or PS) interfaces in Pd-nc-Si(or PS)-p-Si heterostructures. The results revealed that the surface states play an essential role in the carrier transport in both types of heterostructures that were investigated.

The process conditions for a high-efficiency and low cost crystalline silicon solar cell were optimized. Novel approaches such as wafer cleaning and saw -damage removal using 0.5 wt% of 2,4,6-trichloro-1,3,5-triazine, silicon surface texturing with optimized pyramid heights (∼5 μm), and a third step of drive-in after phosphosilicate glass (PSG) removal followed by oxide removal were investigated. A simple method of chemical etching adopted for edge isolation was optimized with edge etching of 5–10 μm, without any penetration of chemicals between the stacked wafers. The conversion efficiency, open-circuit voltage, short-circuit current, and fill factor of the cell fabricated with the optimized process were a maximum of 17.12%, 618.4 mV, 5.32 A, and 77% under AM1.5 conditions, respectively.

Multicrystalline silicon (mc-Si) solar cell fabrication is still a key issue, due to its cost effectiveness compared to crystalline silicon (c-Si). In our present work, a new technique called vapor texturing (VT) is adopted, to achieve effective texturing of mc-Si. Saw damage removal with texturing (SDRWT) using acidic solution was performed on p-type mc-Si wafers with resistivity 0.5–2 Ω cm and thickness 210 μm, using HF:HNO3:CH3COOH:DI water in the ratio 8:21:10:8, for 3 min. An etching depth of about 4 μm is achieved on both sides of mc-Si wafers. The SDRWT-treated mc-Si wafers were vapor textured again by HF:HNO3 in the ratio 7:3, with 8 g of Si. The average reflectance of SDRWT-treated-only and SDRWT with vapor textured mc-Si wafers was 22.16 and 6.5%, respectively. The sheet resistance of SDRWT-treated-only and SDRWT with vapor textured mc-Si wafers was 88 and 50 Ω/□, respectively, after phosphorous doping. Subsequent to effective passivation, a sheet resistance of about 45 Ω/□ was achieved for both SDRWT-treated-only and SDRWT with vapor textured wafers. The effective minority carrier lifetime after vapor texturing and SiNx deposition is about 41.35 μs. Based on SEM analysis, surface morphology shows clear changes after each process.

Surface texturing of silicon can reduce the reflectance of incident light and hence increase the conversion efficiency of solar cells. Comparatively lesser concentrated (10%) standard alkaline (NaOH/KOH) solution does not give good textured multi-crystalline silicon (mc-Si) surface, which could give satisfactory open-circuit voltage. This is due to grain-boundary delineation with steps formed between successive grains of different orientations. In this work an attempt has been made to obtain a well-textured mc-Si surface through three different approaches. The first two are with two different types of acid solutions and the third with concentrated alkaline NaOH. Solutions of HF–HNO3–CH3COOH/H2O system with different concentrations of HF and HNO3 were used for texturing. The results on the effect of texturing of these three solutions on the surface morphology of very large area (125 mm×125 mm) mc-Si wafer as well as on the performance parameters of solar cell are presented in this paper. Attempts have been made to study extensively the surface morphologies of mc-Si wafers in two effective regions of the isoetch curves of the HF:HNO3:diluent's system. Also we studied the reflectance, uniformity, spectral response, short-circuit current, open-circuit voltage, fill factor and dark current–voltage of the cells fabricated using wafers textured with the three different methods. Short-circuit current of the solar cells fabricated using acid-textured wafers were measured to be in the range of 4.93 A. This value is 0.37 and 0.14 A higher than the short-circuit current values measured in the cells fabricated with isotextured and alkaline-textured wafers, respectively.

Transparent conducting aluminium-doped Zinc oxide (ZnO:Al) films have been deposited on glass substrates by magnetron dc sputtering using a ceramic target (ZnO with 2 wt% Al2O3). The dependence of the electrical and optical properties of these films on substrate temperature, sputtering pressure of Ar and location of substrates were investigated in detail. Target is perpendicular with substrate and we controlled the distance ‘x’ of target and substrate. Optimized films with resistivity of 3.7 × 10−4 Ω cm, an average transmission in the visible range (300–800 nm) of greater than 85% and the reflectance in the infrared range being greater than 85% have been formed. Substrate temperature, distance ‘x’, and working pressure are optimized for lower resistivity and high concentration of carriers.

Diamond-like carbon (DLC) films were deposited on corning glass and silicon substrates by the RF-PECVD (Plasma Enhanced Chemical Vapor Deposition) method using methane (CH 4 ) and hydrogen (H 2 ) gases. We examined the effects of the CH 4 to H 2 ratio on the tribological and optical properties of the DLC films. The hardness of the DLC films was measured with a nano-indenter. The optical properties of the DLC thin film were investigated by UV/VIS spectrometry and ellipsometry. From these measurements, we obtained optimum anti-reflection coating at a methane flow rate of 20 sccm. Also, solar cells were fabricated on a silicon substrate using the optimized DLC films as an anti-reflection coating and we obtained an increase of solar cell efficiency of about 20%.

In this work, the fabrication of nanostructures applicable to nano floating gate memory is investigated by using a block co-polymer system composed of Polystyrene (PS) and Polymethylmethacrylate (PMMA). A thin film of self-assembled block copolymer has been used during all experiments for nanostructures with critical dimensions below photolithographic resolution limits. Under suitable conditions, the PS and PMMA self assembled into a honey comb lattice of PMMA in the matrix of PS. Nanoporous thin film from PS-b-PMMA diblock co-polymer thin film with selective removal of PMMA domains was used to fabricate needle-like nanostructures. The reactive ion etching (RIE) was then carried out at room temperature in a single wafer RIE system with the substrate having nano-cylindrical structures. The plasma was excited by radio frequency. Diverse surface nanostructures of sub-100 nm patterning were fabricated by plasma etching using block co-polymer. Finally, we have demonstrated that by combining these self assembled block co-polymers with regular semiconductor processing, a non-volatile memory device with increased charge storage capacity over planar structures can be realized.

Polycrystalline thin films of ZnSxSe1?x with x = 0, 0.25, 0.5, 0.75 and 1.0 have been synthesized using close-spaced evaporation. The films were deposited onto glass substrates at different substrate temperatures in the range 200?400??C. The grown films were characterized using XRD, AFM, EDAX and UV?Vis?NIR spectrophotometer to determine the microstructural properties, composition and optical behaviour. All the ZnSxSe1?x films deposited between 275 and 300??C were crystallized in cubic structure with a single peak that corresponds to the (1?1?1) plane as the preferred orientation. The composition analysis revealed that the films deposited at Ts = 275?325??C were nearly stoichiometric. The average surface roughness for ZnSxSe1?x films deposited at 300??C varied in the range 2?6?nm. The films were highly transparent with optical transmittance >85%. The evaluated energy band gap of the films increased with the increase of sulfur content in the layers and it varied in the range 2.61?3.60?eV. All the layers showed n-type electrical conductivity. The temperature dependence of conductivity was also studied and the activation energy values were evaluated.

In this work, the silicon oxynitride layer was studied as a tunneling layer for non-volatile memory application by fabricating low temperature polysilicon thin film transistors on glass. Silicon wafers were oxynitrided by only nitrous oxide plasma under different radio frequency powers and plasma treatment times. Plasma oxynitridation was performed in RF plasma using inductively coupled plasma chemical vapor deposition. The X-ray energy dispersive spectroscopy was employed to analyze the atomic concentration ratio of nitrogen/oxygen in oxynitride layer. The oxynitrided layer formed under radio frequency power of 150 W and substrate temperature of 623 K was found to contain the atomic concentration ratio of nitrogen/oxygen as high as 1.57. The advantage of high nitrogen concentration in silicon oxide layer formed by using nitrous oxide plasma was investigated by capacitance–voltage measurement. The analysis of capacitance–voltage characteristics demonstrated that the ultra-thin oxynitride layers of 2 nm thickness formed by only nitrous oxide plasma have good properties as tunneling layer for non-volatile memory device.

We have investigated the effects of annealing temperature on the physical and electrical properties of the HfO 2 film deposited by an atomic layer deposition (ALD) method for high- k gate oxides in thin-film-transistors (TFTs). The ALD deposition of HfO 2 directly on the Si substrate at 300 °C results in the formation of thin HfSi x O y interfacial layer between Si and HfO 2 . The subsequent low temperature N 2 -annealing of HfO 2 films (i.e., 300 °C) using a rapid thermal processor (RTP) improves the overall electrical characteristics of HfSi x O y –HfO 2 films. Based on the current work, we suggest that HfO 2 film deposited by the ALD method is suitable for high- k gate oxides in TFTs, which have to be fabricated at low temperature.

In order to characterize a nonequilibrium molecular plasma from the point of view of translational, vibrational and rotational degrees of freedom and their interaction, the characteristic temperatures of such a plasma were measured in an ICP rf reactor. Both pure nitrogen and argon–nitrogen mixture plasmas were examined for this purpose.The experimental results of rotational (Tr), vibrational (Tv) and electron (Te) temperatures are presented. Vibrational and rotational temperatures were measured as a function of nitrogen content for both E and H modes of ICP discharge using a power range of 45–200 W and pressure range of 2.6–13.3 Pa. Additionally, the pressure dependence of electron temperature in a pure nitrogen discharge was studied. Results show that rotational temperature is ≈370 K for E mode and ≈470 K for H mode and almost does not depend on either the applied rf power or the nitrogen content in the discharge. Vibrational temperature groups in the range 5000–12 000 K increase with applied rf power and constantly decay with an increase of nitrogen content. The measured values and behaviour of electron temperature are comparable with those for the positive column of the dc glow discharge. The results also prove that these three temperatures obey the classical inequality Te > Tv > Tr, as well as clarifying the differences in both vibrational and rotational temperature for different modes of the ICP discharge.

ZnSe thin films with different thicknesses are deposited onto glass substrates under a vacuum of 4×10−5 mbar by vacuum evaporation. Rutherford backscattering spectrometry is used to identify the composition of the deposited films. The composition of the deposited films is found to be nearly stoichiometric. The X-ray diffractogram reveals a cubic structure with preferential orientation along the (1 1 1) direction and structural parameters such as crystallite size D, dislocation density δ, strain e, and lattice parameters are calculated. It is observed that the crystallite size increases from 20.11 to 55.56 nm with increase of film thickness. In the DC conduction studies the conduction mechanism is found to follow an exponential trap distribution with density of states 3.251×1048 J−1 m−3. The dielectric constant is calculated as 8.11 [306 K].

Reduction of optical losses in monocrystalline silicon solar cells by surface texturing is one of the important issues of modern silicon photovoltaic. For texturization during commercial monocrystalline silicon solar cell fabrication, a mixture of NaOH or KOH and isopropyl alcohol (IPA) is generally used in order to achieve good uniformity of pyramidal structure on the silicon surface. The interfacial energy between silicon and electrolyte should be reduced in order to achieve sufficient wettability for the silicon surface which in turn will enhance the pyramid nucleation. In this work, we have investigated the role of hydrazine monohydrate as a surface-active additive, which supplies OH− ions after dissociation. This cuts down the IPA consumption during texturing without any loss of uniformity of textured pyramid. We are probably the first group to report such a novel idea of using hydrazine monohydrate addition in NaOH solution for texturization of solar cell. We were able to fabricate monocrystalline silicon solar cells with more than 85% yield in the range of 14–15% efficiency.

A systematic study of the variation in the minority carrier effective lifetime in silicon associated with the different solar cell processing steps in a conventional industrial production line has been carried out using the microwave photoconductive decay (μ-PCD) technique. The solar grade silicon wafers used for this study presented bulk carrier lifetime of ∼10 μs and resistivity 0.5–3 Ω cm. Alkali texturing, phosphorus diffusion using POCl3, thermal oxide growth for surface passivation, plasma etching for edge isolation, and APCVD of TiO2 for surface passivation and antireflection coating were the major steps taken into consideration. The results clearly showed that the lifetime increased as the fabrication process proceeds from the bare wafer with the exception of the step associated to plasma edge isolation. The effective lifetime of the bare wafer was 4.04 μs, which increased to 16.67 μs after the antireflection coating and surface passivation with TiO2. The results of a systematic study of the effective minority carrier lifetime of silicon due to different surface passivation processes are also reported. The results obtained are useful for the design and implementation of proper measures for minority carrier lifetime enhancement during silicon solar cell fabrication at the industrial scale.

We investigated the physical and electrical properties of high-k gate oxide formed by oxidizing multi-layered Hf and Al metal films. We demonstrated that oxidation of multi-layered metal films results in two distinctive amorphous layers: That is, Hf- and Al-doped metal oxide films were formed on the top of silicate film. The thickness of silicate layer and therefore equivalent oxide thickness (EOT) value were dependent on the number of metal films. To reduce the EOT value, higher number of metal layers is desirable. In addition, annealing has to be done at 600 °C to obtain the minimum value of EOT. Hysteresis phenomenon usually observed in high-k oxide was not observed in this work.

Reduction in optical losses in mono-crystalline silicon solar cells by surface texturing is one of the important issues of modern silicon photovoltaics. In order to achieve good uniformity in pyramidal structures on the silicon surface, a mixture of sodium hydroxide (NaOH) or potassium hydroxide (KOH) and isopropyl alcohol (IPA) is generally used during texturization of mono-crystalline silicon solar cell. However, due to the high cost of IPA, there is always a search for alternate chemical which plays the same role as IPA during texturization for industrial solar cell production. For a better texturization, the interfacial energy between silicon and ionized electrolyte of chemical solution should be reduced to achieve sufficient wettability of the silicon surface, which will enhance the pyramid nucleation. In this work, we have investigated the role of hydrazine mono-hydrate as a surface-active additive, which supplies OH − ions after its dissociation. Our process cuts down the IPA consumption during texturing without any loss in uniformity of textured pyramids. We are the first to report the novel idea to add hydrazine mono-hydrate in NaOH solution for texturing mono-crystalline silicon surface to fabricate solar cells with more than 85% yield in the efficiency range of 14.5–15.3%.

We have investigated the annealing effects of HfO 2 films deposited by an atomic layer deposition (ALD) method on the electrical and physical properties in the Si/SiO 2 /Pt/ALD-HfO 2 /Pd metal–insulator–metal (MIM) capacitors. If the annealing temperature for HfO 2 films was restricted below 500 °C, an annealing step using a rapid thermal processor (RTP) improves the electrical properties such as the dissipation factor and the dielectric constant. On the other hand, annealing at 700 °C degrades the electrical characteristics in general; the dissipation factor increases over the frequency range of 1∼4 MHz, and the leakage current increases up to 2 orders at the low electric field regions. We found that the degradation of electrical properties is due to the grain growth in the HfO 2 film (i.e., poly-crystallization of the film) by the high temperature annealing processing. We suggested that the annealing temperature must be restricted below 500 °C to obtain the high quality high- k film for the MIM capacitors.

We investigated the effects of gate voltage (Vgate) on the source-drain current (IDS) measured using either poly(dG)–poly(dC) or poly(dA)–poly(dT) DNA molecules attached on the Au electrodes with a nanometer-sized gap of ∼20 nm. We confirmed that the IDS curves of both poly(dG)–poly(dC) and poly(dA)–poly(dT) DNA molecules can be modulated by simply controlling the magnitude and/or polarity of gate voltage under given humidity level (i.e., 70∼80% in this work). However, different types of IDS modulation were observed from poly(dG)–poly(dC) and poly(dA)–poly(dT), suggesting that the content of DNA molecules has an important role in current formation under the influence of gate voltage. Furthermore, we suggested that the effective diameter of DNA wires is the important factor for deciding the absolute value of IDS in addition to the types of DNA. Based on the current observation, we suggested that poly(dG)–poly(dC) and poly(dA)–poly(dT) DNA molecules might be treated as p- and n-type semiconductor materials, respectively.

We successfully prepared the modified M-DNA molecular wires by the insertion of the divalent zinc ions (Zn2+) in every base pair of λ-DNA molecules. We found that the current–voltage (I–V) characteristics of M-DNA are distinctively different from those measured using other types of DNA molecules including λ-DNA: one of the unique features of the modified M-DNA molecular wires was the metallic property observed in the I–V characteristics (i.e., a linear I–V relationship), suggesting that they might be used to build the metallic nanowire for the future nanodevices. Several parameters such as (1) humidity during the electrical measurement and (2) pH in preparation of M-solution are important factors to decide the I–V characteristics of M-DNA molecular wires. For instance, if the λ-DNA molecules were treated with the pH value of less than 8, they did not show the characteristics of metallic M-DNA molecular wires. In addition, the conductivity of M-DNA molecular wires decreases as the measurement pressure moves to the high vacuum range, although the unique feature (i.e., linear relationship) was maintained even at 10− 5 Torr.

High-efficiency solar cells require printed metal contacts with adapted emitters to ensure high fill factors. Multi-crystalline silicon (mc-Si) substrates require adapting the temperature ramps of rapid thermal processing (RTP) to avoid minority carrier lifetime degradation from activated defect centers. Sufficient temperature difference is required between front and back surfaces during co-firing to prevent junction leakage on the front and proper aluminum back surface field (Al-BSF) on the back surface. Actual temperature profile for co-firing in RTP after screen printing is a key issue for high-quality metal–semiconductor contact for high efficiency solar cell. A novel approach for optimization of co-firing temperature profile in RTP is investigated by measuring the actual temperature of front and back surfaces of the solar cell. Rapid cooling in the spike firing profile is made possible by controlling the gas flow rate in the RTP chamber during co-firing. For the best front and back metal contact and enhancement of minority carrier lifetime, the actual temperature of the silver (Ag)-printed surface is 605 °C and that of Al-printed surface is 743 °C. Mc-Si solar cell with fill factor (FF) 0.79 and conversion efficiency 15.02% is fabricated using the optimized co-firing temperature of RTP in a conventional solar cell production line.

Nanotechnology is one of the newly rising technological fields and acquiring the research priorities in these days. Nanostructures found to have high optical gain, and found to be a key element in the nonvolatile memory devices. The major drawback in the formation of nanocrystalline silicon (nc-Si) is the lack of uniformity and low density. Uniform and packed needle like silicon surface with a size of 50 nm and with a depth of 300 nm was established in the present study using a reactive ion etching (RIE) system. SF 6 and O 2 gases were used for the reactive ion etching process. The ratio of gas flow rates during etching was optimized for the anisotropic etching of silicon to generate nanostructures. Surface morphology was investigated after etching using scanning electron microscope (SEM). The sample etched at an SF 6 flow rate of 13 sccm was found to be smooth, but as the SF 6 flow rate increases, we can see the formation of columnar microstructures. For a typical flow of SF 6 with the flow rate of 22 sccm, we found the silicon surface covered by columnar structures with diameters ∼ 50 nm and depth of about 300 nm. Radio Frequency (RF) power, etching time and oxygen flow rate were fixed to 100 W, 15 min and 12 sccm, respectively, during the experiment for all the samples. In order to observe the effect of RF power on the formation of nanoneedle silicon surface, experiments were carried out at different powers (60 W, 80 W and 100 W) and at a constant SF 6 and oxygen flow rates of 22 sccm and 13 sccm. From this study, we formed a deep nanoneedle structured silicon surface at a power of 100 W. Photoluminescence (PL) and capacitance–voltage ( C – V ) characteristics were recorded on metal-oxide-semiconductor (MOS) capacitors with nanoneedle surface structure of silicon.

In this work, nano-needle structures ate formed to solve problem, related to low density of quantum dots for nano floating gate memory. Such structures ate fabricated and electrical properties` of MIS devices fabricated on the nano-structures are studied. Nano floating gate memory based on quantum dot technologies Is a promising candidate for future non-volatile memory devices. Nano-structure is fabricated by reactive ion etching using and gases in parallel RF plasma reactor. Surface morphology was investigated after etching using scanning electron microscopy Uniform and packed deep nano-needle structure is established under optimized condition. Photoluminescence and capacitance-voltage characteristics were measured in with nano-needle structure of silicon. we have demonstrated that the nano-needle structure can be applicable to non-volatile memory device with increased charge storage capacity over planar structures.

Thin films of InSb have been prepared onto well-cleaned glass substrates at different substrate temperatures (303, 473 and 523 K) by vacuum evaporation. The elemental composition of the deposited InSb films was evaluated by Auger electron spectroscopy (AES) and it was found to be 24% (In) and 76% (Sb). X-ray diffraction patterns indicated the polycrystalline nature of the InSb films with preferential orientation along (1 1 1) plane. Particle size (D), dislocation density ( δ ) and strain ( e ) were determined from the XRD patterns. The particle size increases with the increase of substrate temperature, which was found to be in the range from 8.31 to 24.95 nm. In Laser Raman study, the presence of longitudinal mode (LO) confirms that the deposited films were having crystalline nature. Hall measurements indicate that the films were p-type, having carrier concentration ≅ 1016 cm−3 and mobility (1.1–6.5)×103 cm2/V s.

Multi-crystalline silicon surface etching without grain-boundary delineation is a challenging task for the fabrication of high efficiency solar cells. The use of sodium hydroxide–sodium hypochlorite (NaOH–NaOCl) solution for texturing a multi-crystalline silicon wafer surface in a solar cell fabrication line is reported in this paper. The optimized etching solution of NaOH–NaOCl does not have any effect on multi-crystalline silicon grain boundaries and it also has excellent isotropic etch characteristics, which ultimately helps to achieve higher values of performance parameters, especially the open circuit voltage (Voc) and fill factor (FF), than those in the case of conventional silicon texturing. Easy control over the reaction of the NaOH–NaOCl solution is also one of the major advantages due to which sophistication in controlling the temperature of the etching bath is not required for the industrial batch process. The FTIR analysis of the silicon surface after etching with the current approach shows the formation of Si–Cl bonds, which improves the quality of the diffused junction due to chlorine gettering during diffusion. We are the first to report 14–14.5% efficiency of very large area (150 mm × 150 mm) multi-crystalline silicon solar cells using a NaOH–NaOCl texturing approach in an industrial production line with a yield greater than 95%.

Thin films of TiO2 were deposited by DC magnetron sputtering. The thicknesses of the films were measured using alpha step profilometer technique. Auger electron spectroscopy (AES) is used to determine the composition of the films. The influence of post-deposition annealing at 673 and 773 K on the structural, optical and Raman scattering was studied. The thicknesses of the films were found to be more or less the same irrespective of the annealing temperature and time. XRD results reveal the amorphous nature of the as-deposited film while the annealed samples were found to be crystalline with a tetragonal symmetry. Using the optical transmittance method, the optical constants such as band gap, refractive index and absorption coefficient were calculated and the influence of thermal annealing on these properties was reported. Raman study was employed to study the existence of different frequency modes and improvement of crystallinity of the TiO2 films and the effect of annealing temperature on the Raman shift is studied and reported.

Standard crystalline solar cells are generally fabricated with the front grid pattern of silver paste contact. We have reported a detailed theoretical analysis of the proposed segmented cross grid line pattern in this paper. This work was carried out for the optimization of spacing and width of grid finger, main busbar and sub-busbar. The overall electrical and optical losses due to front contact were brought down to or even less as compared to the usual loss of or more in the conventional screen printed silver paste technology by choosing proper grid pattern and optimizing the grid parameters. The total normalized power loss for segmented mesh grid with plated metal contact was also observed and the total power loss could be brought down to unlike in the case of continuous grid and plated contact. This paper is able to outline the limitations of conventional screen printed contact.

ZnSe thin films were prepared by the vacuum evaporation technique. The influence of substrate temperature on compositional, structural, optical and electrical properties of polycrystalline ZnSe films was investigated using Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), Scanning electron microscopy (SEM), optical transmission and DC conduction studies. The composition analysis shows the nearly stoichiometric nature of the deposited film. The X-ray diffractograms reveals the cubic structure of the film oriented along the (1 1 1) direction. The structural parameters such as particle size [28.41–50.24 nm], strain [1.381–0.785×10−3 lin−2 m−4] and dislocation density [1.285–0.412×1015 lin m−2] were evaluated. Optical transmittance measurements indicate the existence of direct allowed optical transition with a corresponding energy gap in the range of 2.72–2.60 eV. In the DC conduction studies the conduction mechanism is found to be exponential trap distribution and the results are discussed.

Titanium dioxide films have been deposited using DC magnetron sputtering technique onto silicon substrates at an ambient temperature and at an oxygen partial pressure of 7 × 10 –5 mbar and sputtering pressure (Ar + O2) of 1 × 10 –3 mbar. The deposited films were calcinated at 673 and 773 K. The composition of the films as analyzed using Auger Electron Spectroscopy (AES) revealed the stoichiometry with an O and Ti ratio of 2.08. The influence of post-deposition calcination on the Raman scattering of the films was studied. The existence of Raman active modes A1g, B1g and Eg corresponding to the Raman shifts are reported in this paper. The improvement of crystallinity of the TiO2 films as shown by the Raman scattering studies has also been reported. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Zn 0.52 Se 0.48 /Si Schottky diodes are fabricated by depositing zinc selenide (Zn 0.52 Se 0.48 ) thin films onto Si(1 0 0) substrates by vacuum evaporation technique. Rutherford backscattering spectrometry (RBS) analysis shows that the deposited films are nearly stoichiometric in nature. X-ray diffractogram of the films reveals the preferential orientation of the films along (1 1 1) direction. Structural parameters such as crystallite size ( D ), dislocation density ( δ ), strain ( e ), and the lattice parameter are calculated as 29.13 nm, 1.187 × 10 −15 lin/m 2 , 1.354 × 10 −3 lin −2 m −4 and 5.676 × 10 −10 m respectively. From the I – V measurements on the Zn 0.52 Se 0.48 /p-Si Schottky diodes, ideality and diode rectification factors are evaluated, as 1.749 (305 K) and 1.04 × 10 4 (305 K) respectively. The built-in potential, effective carrier concentration ( N A ) and barrier height were also evaluated from C – V measurement, which are found to be 1.02 V, 5.907 × 10 15 cm −3 and 1.359 eV respectively.

Zinc sulfide is a wide band gap semiconductor with high refractive index and hence a promising material for antireflection coating over commercial silicon solar cells. In the present work, attempts have been made to improve the rate of deposition, uniformity of deposited film, stoichiometry, refractive index and the percentage of reflection, respectively, by proper optimization of molar percentage of different CBD ZnS bath chemical constituents and deposition conditions. High values of the rate of film deposition (19.6 A), film uniformity (S.D. 103 mm ×103 mm) mono-crystalline silicon solar cells with CBD ZnS antireflection coating.

Vacuum evaporated GaSe thin films have been characterized using X-ray diffraction, transmission electron microscopy, atomic force microscopy and Auger electron spectroscopy for their structure, surface roughness and composition, respectively. The optical studies show that the as-deposited films possess two indirect and allowed transitions due to spin–orbit splitting of the valence band, as reported here for the first time. DC electrical conduction study has been performed at different field and temperature conditions. Under low electric field (∼2.2×10 5 V cm −1 ) the conduction mechanism is identified as the variable range hopping conduction of Mott's type. The localized states density and the activation energy of this film are found to be 1.686×10 17 cm −3 eV −1 and 0.317 eV, respectively. Space charge limited conduction (SCLC) measurements were performed on a-GaSe films in high electric field (∼3.72×10 5 V cm −1 ) and the SCLC parameters such as free carrier density ( p 0 ), the ratio between free carrier density to the total carrier density ( θ ), mobility ( μ ) were calculated. The trap parameters such as the trap filled limit voltage ( V TFL ), the trap density ( N t ), the depth of dominant trap level ( E t − E v ), the gradient temperature ( T t ) were also calculated and presented. The calculation of all these parameters provides very valuable information on this important semiconductor material.

Forming gas annealing (FGA) of single crystalline commercial silicon solar cell was carried out at various conditions of temperature, pressure, time, and gas ratio for different samples. We report here the role of working pressure during annealing to improve the performance of the solar cells. The improvement basically comes from the surface passivation. It was found that the annealing of solar cells at high temperature in forming gas ambient could bring improvement in conversion efficiency only if the process pressure is sufficient to suppress the out diffusion of hydrogen from the silicon nitride layer that acts as anti-reflection coating. The outcome of this experiment can be instrumental in providing guidelines for improving the low grade commercial cells by introducing an easy and low cost step of forming gas annealing in appropriate condition.

The silicon nitride films were deposited by means of high-density inductively coupled plasma chemical vapor deposition in a planar coil reactor. The process gases used were pure nitrogen and a mixture of silane and helium. Passivated by silicon nitride, solar cells show efficiency above 13%. Strong H-atom release from the growing SiN film and Si–N bond healing are responsible for the improved electrical and passivation properties of SiN film. This paper presents the optimal refractive index of SiN for single layer antireflection coating as well as double layer antireflection coating in solar cell applications.

The interfacial and electrical properties of CVD-W/p-Si 1− x Ge x ( x =0.17)/Si(001) were studied by structural, chemical, and electrical characterizations. W layers were deposited on p-Si 0.83 Ge 0.17 /Si(001) at the growth temperature T s =350–500°C by low pressure chemical vapor deposition (LPCVD) utilizing the WF 6 source gas. Electrical properties of the CVD-W/p-Si 1− x Ge x ( x =0.17) Schottky diodes were characterized by the current–voltage (I–V) measurements. The measured effective Schottky barrier heights (φ BP ) were decreased from 0.434 to 0.378 eV at the reverse bias of 5 V as the deposition temperature, T s , of W layers increases from 350 to 500°C. The structural and chemical properties of CVD-W/p-Si 1− x Ge x ( x =0.17) interfaces were analyzed by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and Auger electron spectroscopy (AES). A strong penetration of W layers into the p-Si 1− x Ge x ( x =0.17) layers caused by the Si and Ge reduction reactions by WF 6 at the initial stages of W film growth was observed.

The interface formation, adhesion and diffusion properties of metals (Cu, Ta, and Ti) and low dielectric constant (low k ) polymer-like organic thin films (POTFs) deposited by plasma-enhanced chemical vapor deposition (PE-CVD) using the para -xylene precursor were investigated. Cu, Ta and Ti deposited on the surfaces of POTFs treated by O 2 and N 2 plasmas generated in a magnetically-enhanced inductively coupled plasma (ME-ICP) reactor. X-ray photoelectron spectroscopy (XPS) was used to study the chemical interactions between metals and POTFs. As a result of formation of new binding states by plasma treatment, the adhesion strength of metals and POTFs was increased. Diffusion properties of metals into POTFs were investigated using Rutherford backscattering spectroscopy (RBS) for the vacuum-annealed Cu/POTFs and Ta/POTFs for 1 h at 450°C. Also, from the RBS spectra, it was observed that Cu and Ta in the post-annealed samples were not diffused into both POTFs with and without plasma surface treatments.

Transparent conducting tin-doped indium oxide (ITO) thin films on polycarbonate and glass substrates were deposited without substrate heating and post-deposition annealing using a dual ion-beam assisted evaporation technique, where the bombardment of the growing film surfaces during electron beam evaporation was done using krypton (varied ion flux, J Kr ., and grid acceleration voltage, V a , of the krypton ion source) and oxygen (fixed ion flux and grid acceleration voltage of the oxygen ion source) ion beams. The electrical, optical, and structural effects of krypton ion-beam bombardment of the growing ITO thin films were investigated using Hall-effect measurements, X-ray photoelectron spectroscopy (XPS), UV-visible spectrometry, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The total film thickness and the deposition rate were 100 nm and 0.06 nm/s, respectively. All ITO films grown with J Kr , = 1.92-3.76 × 10 14 cm -2 s -1 and V a = 100-500 V showed an amorphous structure and no other crystalline phases. As J Kr increased, the electrical conductivity and the optical transmittance of the grown films were improved compared with those of the ITO films deposited using the oxygen ion-beam only. Also, an increase of the bombardment energy by increasing V a of the krypton ion source caused the deterioration of ITO film properties. The conductivity and the optical transmittance of ITO films deposited on polycarbonate substrates were a little lower than those of films on glass substrates. At room-temperature, using optimal growth conditions, the electrical resistivity was as low as 6.4 × 10 -4 Ω cm with an electron carrier concentration n e = 4.3 × 10 20 cm -3 and a Hall mobility μ H = 26.7 cm 2 V -1 s -1 , the visible transmittance (at λ = 550 nm) was 90%, and optical direct band gap energy 3.8 eV.

In this work, a metal-insulator-silicon (MIS) structure with a silicon nitride (SiNx) film, in which silicon nanocrystals (Si-NCs) are embedded as a gate insulator layer, was fabricated on needle-like silicon nanosurfaces. The MIS structure with Si-NCs embedded within the SiNx on the needle-like silicon nanosurface can be used to fabricate nonvolatile memory (NVM) devices with increased charge storage capacities compared to planar structures. In this study, as part of a strategy to overcome the technological and physical constraints involved in scaling down of NVM devices, the charge storage effects associated with the electronic properties of the MIS structure with a silicon substrate having a needle-like nanostructure were evaluated. For fabrication of the needle-like silicon nanosurfaces, polystyrene-block-polymethyl methacrylate (PS-b-PMMA) block copolymer composed of polystyrene (PS) and polymethyl methacrylate (PMMA) was used. The hysteresis width of the capacitance-voltage (C-V) characteristics of the MIS structures embedded with Si-NCs on the silicon substrates of the needle-like nanostructure was greater than that of the MIS structure embedded with Si-NCs fabricated on a planar structure. The interface trap density between the SiNx and uniform needle-like silicon nanosurface was also lower than that of the MIS structure fabricated on a planar structure. Therefore, NVM devices with increased charge storage capacity compared to those fabricated on a planar structure can be realized with a needle-like silicon nanosurface.

The localised back contact method for SiO2/SiNx/SiO2 (ONO) back surface passivated crystalline silicon solar cells has been investigated using a 1064 nm Nd:YAG laser. From the quasi-steady-state-photoconductance measurements, feasible passivation properties of effective carrier lifetime (τeff), back surface recombination velocity (Seff) and diffusion length (LD) with the ONO passivated layer rather than with the SiNx single layer have been confirmed. Localised point back contacts were formed varying with dot diameter and dot spacing and then the cell performance was characterised from solar simulator measurements. It was confirmed that the cell performance is closely related to the back contact area which is determined by dot diameter and spacing, and dot spacing is the more crucial factor to determine the cell performance than diameter variations.

Multicrysalline silicon (mc-Si) materials are commercially important photovoltaic material. This material consists of number of grains and grain boundaries. The orientation is generally random and the size of the grain varies between a few millimeters to several centimeters. So for multicrysalline silicon, surface texturization is not possible with help of standard NaOH/KOH or other anisotropic chemical enchant. Actually texturing for enhanced absorption in silicon has been obtained by creating randomly distributed pyramids using anisotropic wet enchants, but this works well only on single crystalline silicon because of its crystallographic orientation. Various surface texturization method has been used during surface preparation of mc-Si solar cell research, including mechanical grinding, laser-structuring, porous silicon etching, photolithographically defined etching etc. We developed a mask less plasma texturing technique for mc-Si solar cells using high-density hollow cathode plasma etching technique. We used SF/sub 6/ and O/sub 2/ gases in hollow cathode plasma (HCP) dry etching process. This paper demonstrates very high plasma density of 2/spl times/10/sup 12/ cm/sup -3/ at a discharge current of 20mA. Silicon etch rate of 1.3/spl mu/m/min. was achieved with SF/sub 6//O/sub 2/ plasma conditions of total gas pressure =50 mTorr, gas flow rate=40 sccm, and RF power=100W. In this paper, we also reported the surface etching characteristics of monocrystalline silicon and large area multicrystalline silicon (mc-Si) wafer.

Front grid pattern of standard crystalline solar cells is specifically designed for screen printed silver paste contact. A detailed theoretical analysis of the proposed segmented cross grid line pattern has been carried out for optimizing the spacing and widths of the grid finger, main and sub-bus bars. It is shown that by choosing properly the grid pattern and optimizing the grid parameter, the overall front contact electrical and optical losses can be brought down to 10% or less as compared to the usual loss of 15% or more obtained with the conventional screen printed silver paste technology. Limitation of conventional screen printed contact has been pointed out. It was also observed that the total normalized power loss for segmented mesh grid with plated metal contact, the total power loss can be brought down to 10.04 percent unlike 11.57 for the case of continuous grid and plated contact.