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The influence of post-deposition thermal annealing on the thermoelectric properties of n- and p-type nanocrystalline hydrogenated silicon thin films, deposited by plasma enhanced chemical vapour deposition, was studied in this work. The Power Factor of p-type films was improved from 7 × 10 − 5 to 4 × 10 − 4 W/(m.K 2 ) as the annealing temperature, under vacuum, increased up to 400 °C while for n-type films it has a minor influence. Optimized Seebeck coefficient values of 460 μV/K and − 320 μV/K were achieved for p- and n-type films, respectively, with crystalline size in the range of 10 nm, leading to remarkable low thermal conductivity values ( − 1 .K − 1 ) at room temperature.

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.

The breakdown of Fourier's law in nanoscale thermal transport, which has become (ahem) a $h\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}t$ topic lately due to improvements in experimental precision, presents a serious problem for analysis of heat flow. The authors show that the observed discrepancies can be naturally explained by adopting a hydrodynamic extension to Fourier's law. With parameters calculated $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$, this equation shows remarkable agreement with experiments on films of ``holey'' Si. The simplicity of this multiscale model allows numerical solutions for arbitrary geometries using finite-element methods, providing a good tool for interpreting recent experiments with complex setups.

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.

We explore an externally tunable way of producing heat rectification, by means of application of an inhomogeneous distribution of a tensile mechanical stress on heat conducting silicon thin films and graphene ribbons. The resulting strain modifies the thermal conductivity of the material, which, in this way, may be partially tuned from the outside. We calculate the rectification coefficient R as function of the applied strain, of the length of the system, and of the external heat flux. The rectification coefficient of a single device results in R ≃ 1.3 for both systems under consideration. Such a value can be enhanced by connecting in series several devices.

To study the electric and the thermoelectric properties of silicon thin films (SiTFs), we fabricated devices having SiTFs by using conventional complementary metal-oxide-semiconductor (CMOS)-compatible processes for mass production and extendibility. The conductivities and the Seebeck coefficients of SiTFs for dose concentrations of 5 × 1014 cm -2, 1 × 1015 cm -2 and 5 × 1015 cm -2 and for temperatures in the range of 310 to 430 K were measured by using homemade setup. The measured power factors of the SiTFs showed a slight increasing tendency with increasing measurement temperature and were maximum at a dose concentration of 1 × 1015 cm -2 for both n- and p-type films at 330 K.

A surface plasmon resonance based biosensor consisting of SF10 prism, silicon layer, gold thin film and MoS2 enhanced nanosheet is presented. We systematically investigated the SPR reflectivity and resonance angle through the transfer matrix method. Furthermore, with the optimized thickness of gold, silicon and MoS2, we calculated the change of resonance angle to a fixed refractive index change of sample solutions and the full width at half maximum of the reflectivity curves. The excitaition wavelengths of light sources that we use range from 600 nm to 1024 nm which covers both visible and near infrared light. In addition, the optimum configuration for MoS2-enhanced SPR biosensors are monolayer MoS2 and 7 nm silicon layer coated on 50 nm Au thin film with 633 nm as the excitation wavelength. With these optimized parameters we can efficiently increase the sensitivity by ∼10%. Even without the silicon layers, the pure MoS2 enhanced nanosheet can also improve the sensitivity by ∼8%. The performance of MoS2 enhanced nanosheet is almost 3-fold higher than that of graphene. Published version

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.

Degradation in low-temperature polycrystalline-silicon thin-film transistors (LTPS TFTs) after electrical stress was thoroughly investigated in this work. Main channel degradation, abnormal hump generation and hysteresis appearing in the hump region can be observed after positive bias stress. Furthermore, the difference in subthreshold swing (S.S.) values between forward/reverse sweep is observed. The electron trapping into the gate insulator (GI) dominates the main degradation and the hump generation. Additionally, the difference in S.S. values which appears in hump region is attributed to the interface traps and the hysteresis is caused by electron trapping/detrapping into GI.

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

Silicon has proven to have a great potential as anode material in lithium-ion batteries due to its high theoretical electrochemical capacity. However, silicon anodes deteriorate quickly during cyclic charging and discharging, rendering them useless in only a few cycles [1]. This has been attributed to the stresses induced by the large volume change of the material during cycling. Numerous attempts have been made to reduce these stresses, e.g. by using nanoparticles, nanorods, nanowires, thin films and porous structures, with a varying degree of success [2, 3]. While using finely structured materials aids in the intercalation of lithium by reducing the necessary diffusion distance, it also has the unfortunate effect of greatly increasing the specific surface area of the silicon. When using nano-sized materials, silicon’s ability to form a thin and stable solid electrolyte interphase (SEI) therefore becomes increasingly important. There are a number of factors that have a large influence on the SEI formation, making the process notoriously difficult to analyze, but also makes it possible to manipulate. Coating silicon with different nitrides and oxides, e.g. TiN and TiO, have previously been shown to enhance the cycling stability and Coulombic efficiency of the material [4, 5]. In this project the effect of coating the surface of silicon thin films with a thin (< 4-5 nm) layer of silicon nitride is investigated, as well as the effect of varying the stoichiometry of the silicon nitride. By itself silicon nitride has been shown to function as a conversion electrode material, forming elemental silicon and lithium nitride during the initial cycle, with thin films exhibiting capacities of up to 1800 mAh/g [6]. 40 nm silicon thin films were deposited by PECVD on copper foil using silane as precursor. The nitride was formed by addition of ammonia to the gas flow in the late stages of the deposition, and different stoichiometries were obtained by changing the ratio of these gases. By varying the flow rate of ammonia, coatings with four different compositions were made; pure silicon (A), stoichiometric Si3N4(D) and two intermediate compositions (B and C). Three electrodes were punched from each of the resulting films and mounted in coin cells with lithium metal counter electrodes and cycled at a current rate of C/3 for 150 cycles. During cycling, all the cells exhibited an initial increase in capacity, peaking at close-to-theoretical capacity within 10-40 cycles before beginning a slow decline. The average charge capacity for each series after 50, 100 and 150 cycles is presented in the figure, showing that the capacity retention increases with increasing nitrogen content for series A, B and C, and then decreases for series D. This indicates that a nitrogen coating has a positive effect on the deterioration mechanisms of the electrode, and that this effect increases with increasing nitrogen content of the coating, as long as a stoichiometric nitride is not formed. 1. Kasavajjula, U., C. Wang, and A.J. Appleby, Nano-and bulk-silicon-based insertion anodes for lithium-ion secondary cells. Journal of Power Sources, 2007. 163(2): p. 1003-1039. 2. Wu, H. and Y. Cui, Designing nanostructured Si anodes for high energy lithium ion batteries. Nano Today, 2012. 7(5): p. 414-429. 3. Ge, M., et al., Scalable preparation of porous silicon nanoparticles and their application for lithium-ion battery anodes.Nano Research, 2013: p. 1-8. 4. Memarzadeh Lotfabad, E., et al., ALD TiO2 coated silicon nanowires for lithium ion battery anodes with enhanced cycling stability and coulombic efficiency. Physical chemistry chemical physics : PCCP, 2013. 15(32): p. 13646-57. 5. Kohandehghan, A., et al., Silicon nanowire lithium-ion battery anodes with ALD deposited TiN coatings demonstrate a major improvement in cycling performance. Journal of Materials Chemistry A, 2013. 1(41): p. 12850-12861. 6. Suzuki, N., et al., Silicon nitride thin film electrode for lithium-ion batteries. Journal of Power Sources, 2013. 231(0): p. 186-189.

The out-of-plane thermal conductivity of silicon thin film doped with germanium is calculated by non-equilibrium molecular dynamics simulation using the Stillinger-Weber potential model. The silicon thin film is doped with germanium atoms in a random doping pattern with a doping density of 5% and 50% respectively. The effect of silicon thin film thickness on its thermal conductivity is investigated. The simulated thicknesses of silicon thin film doped with germanium range from 2.2 to 10.9 nm at an average temperature 300K. The simulation results indicate that the out-of-plane thermal conductivity of the silicon thin film doped with germanium decreases linearly with the decreasing film thickness. As for the film thickness of 9.8nm and the average temperature ranging from 250 to 1000 K, the investigation shows that the temperature dependence of the film thermal conductivity is not sensitive.

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.

SiOxNy is an innovative material that has recently attracted a lot of attention in different and new applications, ranging from photovoltaics, conductive oxide, carbon capture; nevertheless, due to its complex and multiphase nature, the understanding of its electrical properties is still ongoing. In this framework, the present manuscript presents the investigation of electrical transport properties of nanocrystalline (nc-) SiOxNy. In fact, non-stoichiometric nc-SiOxNy films deposited by Plasma Enhanced Chemical Vapor Deposition have been studied by conductive Atomic Force Microscopy (AFM). The analyses of samples subjected to different thermal treatments conditions and the comparison with nc-Si:H films have allowed us to clarify the role of crystallization and O content on the local conductivity of the layers. We show that the annealing treatment promotes an enhancement of conductance, a redistribution of the conductive grains in the layers and the activation of B doping. Current-voltage characteristics locally performed using the conductive AFM-tip as a nanoprobe have been modelled with thermionic emission transport mechanism. published

This thesis describes the study of silicon thin film materials deposition and the resulting photovoltaic devices fabrication using different types of plasma-enhanced chemical vapour deposition (PECVD) techniques.In the first part, we combine a SiF4/H2 plasma chemistry with the matrix-distributed electron cyclotron resonance (MDECR) PECVD to obtain high growth rate microcrystalline silicon (µc-Si:H). Due to the special design of MDECR system, careful investigation of the impact energy of impinging ions to material deposition can be accessible. We find that moderate ion energy conditions is beneficial to achieve a significant drop in the density of nano-voids, thus a higher quality material with better stability can be obtained. A two-step deposition method is introduced as an alternative way to eliminate the existence of amorphous incubation layer during film growth.The second part of work is dedicate to the exploration of the Tailored Voltage Waveforms (TVWs) excitation technique for capacitively coupled plasmas (CCP) processes. As an advantage over the conventional sinusoidal excitations, TVWs technique provide an elegant solution for the ion flux-energy decoupling in CCP discharges through the electrical asymmetry effect, which makes the independent study of the impact of ion energy for material deposition at relatively high process pressure possible. Based on this insight, we have studied the deposition of µc-Si:H and amorphous silicon (a-Si:H) from the SiF4/H2/Ar and SiH4/H2 plasma chemistry, respectively. From the structural and electronic properties analysis, we find that the variation of ion energy can be directly translated into the material quality. We have further applied these results to photovoltaic applications and established bottom-up links from the controllable plasma parameters via TVWs to the deposited material properties, and eventually to the resulting device quality.In the last part, as a further application of TVWs, an “electrode-selective” effect has been discovered in the CCP processes. In the case of silicon thin film deposition from the SiF4/H2/Ar plasma chemistry, one can achieve a deposition process on one electrode, while at the same time either no deposition or an etching process on the counter electrode. This is due to two effects: the multi-precursor nature of the resulting surface process and the asymmetric plasma response through the utilization of TVWs. Moreover, such deposition/etching balance can be directly controlled through H2 flow rate. From a temporal asymmetry point of view, we have further studied the impact of process pressure and reactor geometry to the asymmetric plasma response for both the single-gas and multi-gas plasmas using the sawtooth waveforms. The product of pressure and inter-electrode distance P·di is deduced to be a crucial parameter in determine the plasma heating mode, so that a more flexible control over the discharge asymmetry as well as the relating “electrode-selective” surface process can be expected., Ce manuscrit présente l'étude de la fabrication de couches minces de silicium basée sur des différents types de dépôt chimique en phase vapeur assisté par plasma (PECVD) pour des applications dans le photovoltaïque. Tout d'abord, nous avons combiné une chimie du plasma halogéné en utilisant un mélange de SiF4/H2 et la technique plasmas distributés matriciellement à résonance cyclotronique électronique (MDECR) PECVD pour le dépôt de μc-Si:H à grande vitesse. Nous trouvons que les conditions d'énergie ionique modérée sont bénéfiques pour obtenir une diminution significative de la densité des nano-vides, et ainis nous pouvons obtenir un matériaux de meilleure qualité avec une meilleure stabilité. Une méthode de dépôt en deux étapes a été introduite comme moyen alternatif d'éliminer la formation d'une couche d'incubation amorphe pendant la croissance du film. Ensuite, nous avons exploré la technique d'excitation Tailored Voltage Waveform (TVW) pour les processus plasma radiofréquence capacitivement couplé (RF-CCP). Grâce à l'utilisation de TVW, il est possible d'étudier indépendamment l'influence de l'énergie ionique sur le dépôt de matériaux à une pression de processus relativement élevée. Basé sur ce point, nous avons étudié le dépôt de μc-Si:H et a-Si:H à partir des plasma de SiF4/H2/Ar et de SiH4/H2, respectivement. A partir d'une analyse des propriétés structurelles et électroniques, nous constatons que la variation de l'énergie ionique peut directement traduite dans la qualité du matériaux. Les résultats se sont appliqués aux dispositifs photovoltaïques et ont établi des liens complets entre les paramètres de plasma contrôlables par TVW et les propriétés de matériaux déposé, et finalement, les performances du dispositif photovoltaïque correspondant. Enfin, nous avons trouvé que dans le cas du dépôt de couches minces de silicium à partir du plasma de SiF4/H2/Ar à l'aide de sawtooth TVW, on peut réaliser un processus de dépôt sur une électrode, sans aucun dépôt ou gravure. contre-électrode. Ceci est dû à deux effets: la nature multi-précurseur du processus de surface résultant et la réponse de plasma spatiale asymétrique par l'effet d'asymétrie de pente de la sawtooth TVW. La découverte de tels procédés “electrode-selective” encourage la perspective que l'on puisse choisir un ensemble de conditions de traitement pour obtenir une grande variété de dépôts désirés sur une électrode, tout en laissant l'autre vierge.