Search

Pulsed laser absorption-mediated explosive crystallization of silicon films has extensively been studied using microscopy techniques on single laser pulse-irradiated regions in the literature. In this work, we experimentally demonstrate and theoretically explain in detail the use of slow quenching regime for laser crystallization mediated by highly overlapping pulses. Increasing the use of Si in thin film transistors and photovoltaic applications drives researchers to find cost-effective and efficient ways of manufacturing crystalline Si films on various types of substrates. Understanding the mechanism of the laser crystallization process of Si films by pulsed lasers becomes crucial. This work reveals the laser crystallization mechanism of Si thin films in macroscopic scales by considering heat transfer and accumulation dynamics. Our motivation is to describe the dynamics of the laser crystallization of Si films to provide a complementary guide for the production of device-grade c-Si films by infrared pulsed laser without employing preheated substrates. c-Si grains exceeding 2 mm in size were formed by laser crystallization of 1 mu m-thick Si films without any pre/postannealing step at room temperature and within a typical continuous wave irradiation-based light energy budget, which we think to be the most important achievement of our work.

Silicon is a leading candidate material to replace carbon/graphite, the commonly used anode material in lithium-ion batteries (LIBs), because it has an 11 times higher theoretical specific capacity. However, silicon anodes have two main issues, low electronic conductivity and large volume expansion during cycling, and these issues present challenges in the manufacture of mechanically stable high-electrochemical-performance Si electrodes. Physical vapor deposition (PVD) is an alternative fabrication process that can produce binderless compact Si thin films suitable for microbatteries and thin flexible devices. Despite numerous studies exploring the use of vacuum-based PVD silicon films, no definitive information has been recorded correlating how changes in process parameters affect the properties of the resulting deposited films and how this influences anode performance in Li-ion batteries. In this work, process parameters (i.e., deposition power and gas working pressure) were altered for various Si film deposition trials. Electronic resistivity, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), residual film stress, X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) measurements were performed for a thorough physico/chemico analysis of the various films. This information was used to interpret the differences in discharge capacity and capacity retention obtained from the various Si anodes using galvanostatic charge/discharge cycling from assembled coin cells. CV measurements were used to corroborate performance outcomes, as well as to calculate Li-ion diffusion coefficients Refereed/Peer-reviewed

Since the beginning of the coronavirus disease 2019 (COVID-19) in December 2019 and the current lack to date of specific drugs or vaccinations to cope with the disease, it has become apparent that the surest way of dealing with this is through early diagnosis and management. Current testing has shown to be unable to rapidly and accurately provide the results required to restrict the spread. Here we report feasibility for the use of an intrinsic silicon thin film transistor functionalised with aptamers designed to attach to the spike protein of COVID-19. It is shown that a linear response can be obtained in a concentration range of 1 pM to 1 nM.

Since the beginning of the coronavirus disease 2019 (COVID-19) in December 2019 and the current lack to date of specific drugs or vaccinations to cope with the disease, it has become apparent that the surest way of dealing with this is through early diagnosis and management. Current testing has shown to be unable to rapidly and accurately provide the results required to restrict the spread. Here we report the use of an intrinsic silicon thin film transistor functionalised with aptamers designed to attach to the spike protein of COVID-19. It is shown that a linear response can be obtained in a concentration of 10 fM and 10 pM, and that the relative response is independent of the applied potential allowing a sensory system to fine tune the applied potential to facilitate the interpretation of the results.

In this paper we provide a design for a vertical grating coupler for a silicon thin film on lithium niobate. The parameters-such as the cladding layer thickness of lithium niobate, fiber position, fiber angle, grating period, and duty cycle are analyzed and optimized to reduce the mode mismatch loss and the internal reflections. The alignment tolerances, for the grating coupler parameters, are also simulated and evaluated. We determine that our simulated grating coupler exhibits high efficiency, enhanced light coupling, and high alignment tolerance.

This paper investigates the light absorption property of nanostructured dielectric reflectors in silicon thin film solar cells using numerical simulation. Flat thin film solar cell with ZnO nanostructured back reflector can produce comparable photocurrent to the control model with Ag nanostructured back reflector. Furthermore, when it is integrated with nano-pillar surface decoration, a photocurrent density of 29.5 mA/cm2 can be achieved, demonstrating a photocurrent enhancement of 5% as compared to the model with Ag nanostructured back reflector.

We study light trapping in hydrogenated amorphous silicon thin film solar cells fabricated by plasma-enhanced chemical vapor deposition on various nanostructured back reflectors. The back reflectors are patterned using polystyrene assisted lithography. We have investigated the correlation between the back reflector optical properties and the corresponding solar cell performance. We have introduced double size polystyrene sphere patterned back reflectors and have provided experimental evidence for improved light trapping performance compared to single size polystyrene sphere patterned back reflectors. We have achieved high performing nanostructured amorphous silicon solar cells with an initial power conversion efficiency of 7.53% and over 20% enhancement of the short-circuit current compared with the reference flat solar cell.

Al-doped ZnO (AZO) thin films are deposited using dc magnetron sputtering and the process conditions are optimized to obtain transparent conducting electrode (TCE) with desirable properties suitable for photovoltaic applications. In the course, the effects of deposition parameters such as growth temperature, deposition time and plasma power density on the structural and optoelectronic properties were investigated using suitable characterization techniques. XRD analysis of the deposited films at different process conditions showed a strong c-axis preferred orientation. The surface roughness of the deposited films was examined using AFM analysis. Elemental analysis was carried out using XPS. The resistivity and sheet resistance of the thin films decreased with increase in temperature, deposition time and power density. The optimized films deposited at 250 °C resulted in electrical resistivity of 6.23 × 10−4 Ωcm, sheet resistance of 9.2 Ω/□ and exhibited an optical transmittance of >85% in the visible range. Figure of merit (FOM) calculations were carried out to analyze the suitability of deposited thin films for thin film amorphous silicon solar cell applications. The photogain of optimized intrinsic a-Si:H layer was in the range of 104, whereas no photogain was observed in doped a-Si:H layers. The thin film solar cell fabricated using the optimized AZO film as TCE exhibited power conversion efficiency of 6.24% when measured at AM 1.5 condition.

Based on well-defined lab conditions, we have developed experimental methods to characterize bifacial laser crystallized multicrystalline silicon (mc-Si) thin film solar cells fabricated on glass. Key parameters which determine the performance of the bifacial solar cells such as light intensity and incidence angle dependence on both sides have been characterized. From these parameters and the local irradiance data, the annual power output of the bifacial solar cells can be simulated easily. In addition, bifacial measurements under well-defined conditions using a single sun simulator have been performed by means of a mirror. The best bifacial mc-Si thin film solar cell shows a “bifacial efficiency” of 12.4% compared to state of the art monofacial mc-Si thin film counterpart of 12.1%. According to our simulation, even a “bifacial efficiency” above 14% is realistic if the solar cell is installed in front of a white diffuse scattering surface with a reflectance of ~90%. A threshold of 24% additional light contribution at which the bifacial mc-Si thin film solar cells outperform the monofacial ones have been determined by simulations. This shows that the advantages of the bifacial cells can already be observed at very low level (

A frequency-dependent phonon Boltzmann transport equation solver is presented to numerically study the lattice thermal conductivity of nano-porous silicon thin film based on the Discrete Ordinates Method. We find that not only characteristic size and porosity, but also the shapes of both unit cell and pore do affect the lattice thermal conductivity. Therefore, we arranged a series of computational cases by the orthogonal design method to investigate the influence of geometric parameters Lx, Ly, ax/Lx and ay/Ly (Lx is unit cell length, Ly unit cell width, ax pore length and ay pore width). Furthermore, a non-linear regression model is established depending on the data obtained from those computational cases. The result shows that lattice thermal conductivity of nano-porous silicon thin film decreases obviously with the increase of ax/Lx and ay/Ly. Among these four geometric parameters, ay/Ly is the most significant factor while Lx and Ly have little effect on lattice thermal conductivity. The proposed regression model can offer useful suggestion for the fabrication of nano-porous silicon thin film with lower lattice thermal conductivity.

We develop a method to quantify the local minority carrier diffusion lengths in interdigitated back-contact solar cells having a 10- µ m-thick liquid-phase crystallized (LPC) Si absorber by light-beam induced current (LBIC) measurements. The method is verified by 2-D simulations of the LBIC signals using ASPIN3. The effective minority carrier diffusion lengths determined this way range between 33 and 44 µ m inside a grain, which proves that advanced cell concepts like an interdigitated back contact (IBC) system are well suited for the LPC absorbers. Furthermore, the method has the potential to help improve the optimization of contact system geometries, and it may be used to understand the influences of different grain orientations and improve the LPC-Si absorber fabrication process.

This is the peer reviewed version of the following article: Martín, I., López, G., Plentz, J., Jin, C., Ortega, P., Voz, C., Puigdollers, J., Gawlik, A., Jia, G. and Andrä, G. (2019), Multicrystalline Silicon Thin‐Film Solar Cells Based on Vanadium Oxide Heterojunction and Laser‐Doped Contacts. Phys. Status Solidi A, 216: 1900393, which has been published in final form at https://doi.org/10.1002/pssa.201900393. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. Liquid phase crystallized (LPC) silicon thin films on glass substrates are a feasible alternative to conventional crystalline silicon (c-Si) wafers for solar cells. Due to substrate limitation, a low-temperature technology is needed for solar cell fabrication. While silicon heterojunction is typically used, herein, the combination of vanadium oxide/c-Si heterojunction as emitter and base contacts defined by IR laser processing of phosphorus-doped amorphous silicon carbide stacks is explored. LPC solar cells are fabricated using such technologies to identify their issues and advantages with a promising performance of an active-area efficiency of 5.6%. Apart from the absence of light-trapping techniques, the relatively low efficiency obtained is attributed to a low lifetime in the LPC silicon bulk. These poor material properties imply a short diffusion length that makes it that only photogenerated carriers in the emitter regions can be collected. Consequently, future devices should show narrower base contact regions, suggesting a shorter-wavelength laser, combined with longer LPC substrate lifetimes.

In this work, we investigated the negative capacitance (NC) effect of ferroelectric HfAlO on the poly-silicon thin film transistor devices using high-$\kappa$ HfO 2 gate insulator by simulation. Excellent performances were achieved, including a high on-state drive current, a high I on /I off of $\gt10^{7}$ and a low subthreshold swing of 58 mV/dec. These enhanced performances were related to the strong ferroelectric polarization inducing NC effect to obtain excellent gate controllability.

In this paper using optical emission spectroscopy (OES) to monitor In-line very high-frequency plasma enhanced chemical vapor deposition (VHF-PECVD) technique optoelectrical properties. In-line VHF-PECVD was developed by MIRDC (Metal Industries Research & Development Centre) in Taiwan. In-line VHF-PECVD system with an electrode distance was 15 to 50 mm and electrode area of 1681 cm2. Due to the difference between the observation port and the plasma position. Therefore, this paper developed an online VHF-PECVD internal optical system to verify the stability of the internal optical system. The OES is a non-intrusive monitoring device that is widely used for real-time monitoring and stabilization devices for plasma monitoring. This paper used OES to monitor the stability of processed silicon thin films.

Laser induced diverse silicon nano-porous structures were studied to comprehend its light absorption capabilities within visible range of light. In addition, various characterization methods like SEM, light-spectroscopy, and EDX were employed for sound comprehension.

We develop a first-principles method to simulate the propagation of intense and ultrashort pulsed light in crystalline thin films solving the Maxwell equations for light electromagnetic fields and the time-dependent Kohn-Sham equation for electrons simultaneously using common spatial and temporal grids. As a demonstration, we apply the method to silicon thin films.

Polysilicon thin film transistors have broad application prospects in high-performance flat panel displays and flexible wearable devices due to their high carrier mobility and good stability. However, due to process conditions and other reasons, there are traps inside, and under some electrical stress conditions, its electrical properties will degrade. Here we report the changes in electrical characteristics of p-type polysilicon thin film transistors with stress time at a negative gate voltage of -20V and a temperature of 60°C. It is obtained that the transfer characteristics of the p-type polysilicon thin film transistor move in the negative direction with the increase of Negative Bias Temperature Instability time, and with the increase of SS degradation, and the total trap state inside it is calculated by SS, which provides a theoretical basis for improving the reliability of the device.

In this study, the time response behavior of low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) to x-ray irradiation pulses with different frequencies is analyzed. The formulas for the time response of excited and recovery behaviors are proposed for possible use in circuit performance enhancement in real x-ray irradiation situations. The predicted and measured results fit fairly well, which is important in the development of x-ray image sensors using LTPS TFTs.

Emissive micro-LED technologies have been a topic of recent interest as a means to build high-luminance displays for direct-view micro-LED displays and micro-LED microdisplays. The promise of an emissive technology coupled with the efficiency and luminance of III-V LEDs has been studied for many years. With the prevalence of LEDs, the barrier for integration with transistor technologies to form arrays and display technologies has lowered. We present an overview of various micro-LED technologies and our focus on micro-LED microdisplays using our thin-film integration method.

Here an in situ system is presented to simultaneously study the evolution of both morphology and stress in the silicon thin film electrode during lithiation and delithiation. Owing to the specific design with two observation windows in the in situ cell, both the curvature and color of the silicon thin-film electrodes upon lithiation and delithiation processes can be measured by multi-optical sensor and optical microscope. By such colorimetric method, the color evolution can be used to represent the thickness of silicon thin film electrode, and the quantitative relationship can be obtained by in situ atomic force microscope and optical microscopy experiments. Combining the real thickness with Stoney equation, the accurate stress of the LixSi film can be obtained during the electrochemical cycles.

We study light trapping and parasitic losses in hydrogenated amorphous silicon thin film solar cells fabricated by plasma-enhanced chemical vapor deposition on nanostructured back reflectors. The back reflectors are patterned using polystyrene assisted lithography. By using O2 plasma etching of the polystyrene spheres, we managed to fabricate hexagonal nanostructured back reflectors. With the help of rigorous modeling, we study the parasitic losses in different back reflectors, non-active layers, and last but not least the light enhancement effect in the silicon absorber layer. Moreover, simulation results have been checked against experimental data. We have demonstrated hexagonal nanostructured amorphous silicon thin film solar cells with a power conversion efficiency of 7.7% and around 34.7% enhancement of the short-circuit current density, compared with planar amorphous silicon thin film solar cells. Published version

Raman spectroscopy is a powerful technique for revealing spatial heterogeneity in solid-state structures but heretofore has not been able to measure spectra from multiple positions on a sample within a short time. Here, we report a novel Raman spectroscopy approach to study the spatial heterogeneity in thermally annealed amorphous silicon (a-Si) thin films. Raman spectroscopy employs both a galvano-mirror and a two-dimensional charge-coupled device detector system, which can measure spectra at 200 nm intervals at every position along a sample in a short time. We analyzed thermally annealed a-Si thin films with different film thicknesses. The experimental results suggest a correlation between the distribution of the average nanocrystal size over different spatial regions and the thickness of the thermally annealed a-Si thin film. The ability to evaluate the average size of the Si nanocrystals through rapid data acquisition is expected to lead to research into new applications of nanocrystals.

We introduce a photonic crystal cavity array realised in a silicon thin film and placed on polydimethlysiloxane (PDMS) as a new platform for the in-situ sensing of biomedical processes. Using tapered optical fibres, we show that multiple independent cavities within the same waveguide can be excited and their resonance wavelength determined from camera images without the need for a spectrometer. The cavity array platform combines sensing as a function of location with sensing as a function of time.

In this paper, the longitudinal magneto-optical Kerr effect (MOKE) properties of the quadrilayer structure HfO2/Co/HfO2/Al/silicon are investigated experimentally and theoretically. The cavity enhancement of HfO2 on the magneto-optical (MO) Kerr response of the quadrilayer has been confirmed. The giant longitudinal Kerr rotation of −1.04° at wavelength of 570 nm is tested when the cap and intermediate HfO2 layer thicknesses are 15 nm and 30 nm, respectively. The longitudinal Kerr rotation reversal in the wavelength range (440–720 nm) is also observed. It is strongly suggested that the enhanced MOKE stems from the optical reflection and interference of the quadrilayer structure.

The authors review selected topics in the development of hydrogenated amorphous silicon (a‐Si:H), from its emergence some 50 years ago to its present status as a mature thin‐film semiconductor, with market successes including flat‐panel displays, solar modules, and x‐ray scanners. By altering process gas mixtures and deposition conditions, films with a range of atomic, structural, and amorphous/crystalline phase compositions may be deposited, offering tunable bandgap, refractive index, and light‐scattering properties. Films thus “functionalized” have greatly increased scope and utility. Three emerging applications are reported, and more extensive sections on two topics of current importance are presented: 1) Multi‐junction thin film silicon solar cells for water splitting applications; and 2) thin‐film silicon solar cells on flexible substrates.

The aim of this study is the optimization of the antireflection effect of SiN x in silicon on glass based structure. A numerical calculation is performed and a SiNx double stack antireflection coating is found to have significant advantages over single-layer due to their broad-range coverage of the solar spectrum. Moreover, it was found that minimum reflection losses is obtained for SiN x /SiN x double-layer ARC with refractive indexes of 1.9 et 2.3 for the top and the bottom layer, respectively. The effect of the incident angle on reflectance is also studied. The numerical optimization procedure and its results are presented.

We developed a method to quantify the local minority carrier diffusion lengths in interdigitated back-contact solar cells having a 10 μm thick liquid phase crystallized (LPC) Si absorber by light-beam induced current (LBIC) measurements. The method is verified by 2-D simulations of the LBIC signals using ASPIN3. The effective minority carrier diffusion lengths determined this way range between 33–44 μm inside a grain, which proves that advanced cell concepts like an IBC system are well suited for the LPC absorbers. Furthermore, the method has the potential to help improving the optimization of contact system geometries and it may be used to understand the influences of different grain orientations and improve the LPC-Si absorber fabrication process.

We have applied the photocapacitance method to the measurements of hole drift-mobilities in silicon solar cells. We found a simple analysis that yields drift-mobilities even in the presence of anomalously dispersive transport. On one thick sample we measured the hole drift-mobility using both the photocapacitance and the time-of-flight methods; the two methods gave results that were consistent with each other and with the established bandtail multiple-trapping model. We then applied the method to thinner samples that are more characteristic of the conditions in solar modules, but are not generally usable for the time-of-flight method. These samples showed much smaller hole drift-mobilities than expected from the bandtail trapping model. We speculate that the hole drift-mobility has smaller values in regions close to the substrate during deposition than has been reported for thicker samples.

Peak power density stability and beam-wander precision of probe laser are important factors affecting the inspection results in the precision thin film optical measurements. Pinhole is frequently used as a spatial filter in the optical inspection system. In this work, four different diameters of pinhole are investigated experimentally. It is found that pinhole diameter of 0.3 mm is considered to be a promising candidate for mounting in front of probe laser for silicon thin film optical inspection due to better peak power density stability and better beam-wander precision.

Excimer laser annealing (ELA) is frequently employed to fabricate low-temperature polycrystalline silicon films on glass substrate. The grain size and crystallinity of polycrystalline silicon films are significantly affected by the resolidification behavior during ELA. A real-time in situ time-resolved optical measurement system is developed to record the rapid phase transformation process during ELA. The average solidification velocity of liquid-Si is calculated from these optical spectra using MATLAB and Excel softwares. Field emission scanning electron microscopy images reveal maximum grain size of poly-Si films with a diameter of 1 μm, which is obtained in the complete melting regime of both frontside ELA and backside ELA. Recrystallization mechanisms of complete melting of Si thin films in frontside ELA and backside ELA are demonstrated. Resolidification scenarios of partial melting, near-complete melting and complete melting in frontside ELA and backside ELA are proposed.

The hysteresis effect observed in the transfer characteristics of n-channel bottom-gate hydrogenated polymorphous silicon (pm-Si:H) thin-film transistors (TFTs) is investigated in terms of the channel width. Such phenomenon is observed in devices of wide channel (>20 μm), whereas it diminishes in devices of narrow channel. The hysteresis of wide channel TFTs is mainly due to charges injected from the channel, trapped in the gate dielectric. As the channel width is reduced the edge effect becomes more significant and the effect of carrier injection from the channel is eliminated, which is balanced by the effect of charge injection from the gate electrode.

To stabilize the electric characteristic of Silicon Thin Film Transistor, reducing the current leakage is most important issue. To reduce the current leakage, many ideas were suggested. But the increase of mask layer also increased the cost. On this research Bird's Beak process was use to present element. Using Silvaco simulator, it was proven that it was able to reduce current leakage without mask layer. As a result, it was possible to suggest the structure that can reduce the current leakage to 1.39nA without having mask layer increase. Also, I was able to lead the result that electric characteristic (on/off current ratio) was improved compare from conventional structure.