Nanocrystalline Silicon Thin Films Research Articles

Investigation structural heterogeneities in hydrogenated nanocrystalline silicon thin films from argon-diluted silane dusty plasma PECVD

This study presents a novel approach for achieving a high deposition rate of nanocrystalline hydrogenated silicon (nc-Si:H) thin films using dusty plasma, eliminating the need for hydrogen dilution. Contrary to conventional beliefs, the research demonstrates that crystalline seeds can nucleate directly from the plasma environment itself. The investigation explores the relationship between plasma parameters and the degree of crystallinity in the deposited films, along with the characterization of structural inhomogeneities throughout the film's thickness. Raman spectroscopy, X-ray diffraction, and Transmission Electron Microscopy (TEM) are utilized for detailed analysis. The results reveal intriguing variations in crystallinity along the film's thickness, with higher crystallinity observed near the surface compared to regions closer to the substrate interface. In-depth analysis of grain size variation reveals that the average crystallite size decreases near the surface and increases in the bulk volume of the material. Additionally, deposition parameters, specifically power and pressure, are found to influence grain sizes, with higher values promoting larger grain growth. Notably, the observation of conical growth in layers deposited from dusty plasma presents a promising avenue for achieving controlled and desirable microstructures. This study sheds light on the critical influence of deposition parameters on film properties and the potential of dusty plasma for achieving desirable microstructures in nc-Si:H thin films. The findings offer valuable insights for tailoring thin film properties in diverse technological applications.

High conductivity characteristics of phosphorus-doped nanocrystalline silicon thin films by KrF pulsed excimer laser irradiation method.

The microstructure and high conductivity properties of phosphorus-doped nanocrystalline silicon films were investigated on samples prepared by a plasma-enhanced chemical vapor deposition technique and the KrF pulsed excimer laser irradiation method. The results of Fourier transform infrared spectroscopy and Raman spectroscopy show that Si nanocrystallites with an average diameter of 2 nm to 3 nm are formed in the film. The degree of crystallinity increases with the increase of laser radiation intensity, while the content of hydrogen decreases gradually. More phosphorus atoms are substitutionally incorporated into the nc-Si dots under higher laser irradiation fluence, which is responsible for the high dark conductivity. By controlling the laser fluence at 1.0 J cm-2, the dark conductivity as high as 25.7 S cm-1 can be obtained. Based on the measurements of temperature-dependent conductivity, the carrier transport processes are discussed. The phosphorus doping and the increase of electron concentration are considered to be the reason for high dark conductivity and extremely low conductivity activation energy.

Superior Phosphorous Doping in Nanocrystalline Silicon Thin Films and Their Application as Emitter Layers in Silicon Heterojunction Solar Cells

Phosphorous doping in the nc-Si network induces gradually reduced crystallinity; however, preferential growth along <220>-oriented crystallites promotes the columnar-like growth morphology. At optimum doping, substitution by donor P+-atoms in the c-Si lattice contributes surplus free electrons and high carrier mobility, resulting in superior electrical conductivity in the n-nc-Si network. An elevated doping leads to incorporating elemental P0 atoms in the interstitial position or forming P–Si–H clusters and generating voids between the crystalline columns. Segregation of defects contributes to decreasing carrier mobility and reducing conductivity after diminishing crystallinity and narrowing the optical band gap. By precisely controlling the growth at 250 °C and efficient electrically active doping by P+-atoms, n-nc-Si thin films with superior dark conductivity (∼101 S cm–1) are produced in which the percolation of charge carriers through the crystalline columns could facilitate stacked-layer devices. The optimum n-nc-Si thin films are used as the emitter layers in n-nc-Si/p-c-Si heterojunction solar cells (HJSCs). Furthermore, an ultrathin a-Si:H buffer layer on the p-c-Si minimizes the junction carrier recombination loss, and subsequent postdeposition short-time H-plasma treatment (PSHPT) ensures seeds for superior nanocrystallization in the n-nc-Si emitter layer. The n-nc-Si/(PSHPT)i-nc-Si(buffer layer)/p-c-Si HJSC delivers a PV conversion efficiency, η ∼12.35%, via a reasonable fill factor of ∼0.647 and sensible JSC of ∼32.75 mA cm–2. Further improvement in the PV performance could be possible using suitably thinner p-c-Si wafers, harmonizing with the effective carrier diffusion length, and fabricating a high-quality passivation structure on the backside.

Growth, structural and vibrational properties of hydrogenated nanocrystalline silicon thin films prepared by radiofrequency magnetron sputtering technique at room temperature

The main objective of this paper is to produce the hydrogen-free and hydrogenated nanocrystalline silicon (nc-Si:H(x)) thin films deposited onto the single-crystalline Si(100) wafer by radio-frequency magnetron sputtering (RF-MS) at a substrate temperature of ∼ 300 K. Sputtering was effectuated by a microwave plasma in a mixture of argon and hydrogen (Ar + (H2(x)) gasses taken at different proportions of hydrogen dilution: x = 0, 2.5, and 5 sccm (standard cubic centimeter per minute). The deposition rates of the nc-Si:H were fully controlled, and the thickness of these films was ∼ 200 and 300 Å. Pt-capping layer was deposited in order to protect the nc-Si:H layer from oxidation. The thickness of the capping layer was fixed at ∼ 5 Å.The effects of the hydrogen flow rate and post-growth thermal treatment on the crystalline structure and morphology of as-grown nanocrystalline silicon thin films were systematically investigated by ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS), atomic force microscopy (AFM), grazing incidence x-ray diffraction (GI-XRD) and micro-Raman spectroscopy methods. From the measured data, the average nanocrystallite sizes, surface morphology and other important characteristics of these thin films were analyzed. The grown nc-Si:H thin films may be used as a semiconducting electrode material for electrochemical proton production, which is of great technological importance, especially for solid-state electrochromic device applications.

High-Quality Nanocrystalline Silicon (nc-Si:H) Thin Film With Mixed-Phase and Its Application of Circulating Tumor Cell DEP Biochip

This paper proposes the light-induced dielectrophoresis (DEP) biochip prepared by 40.68-MHz very high-frequency plasma-enhanced chemical vapor deposition (VHFPECVD) and post- microwave annealing treatment. The biochip can screen circulating tumor cells without using any antibodies and biomarkers. Therefore, the biochip’s high efficiency and high purity are goals for effectively conducting the whole genome sequencing (WGS) analysis. The quality, uniformity, and electrical properties of the prepared silicon thin films affect the performance parameters of the biochip. High-quality nanocrystalline silicon (nc-Si:H) thin film is the core technology in the biochip. High-density nc-Si:H thin films can be well prepared using 40.68 MHz VHFPECVD and post-treatment microwave annealing. Microwave annealing improves the crystallinity and reduces the defects in the nc-Si:H thin films discovered by Fourier-transform infrared spectroscopy (FTIR). The prepared thin film with a crystallinity of 5% enhanced 38.3%, surface roughness of 10.93 nm, and a photo/dark current of 7.1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> with a power density of 60mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was obtained. The biochip showed a recovery rate of 81.3%, purity of 78.6%, and survival rate of 91% for applying to the circulating tumor cells (CTCs).

Fabrication of N-Type Nanocrystalline Silicon Thin-Film by Magnetron Sputtering and Antimony Induced Crystallization

The fabrication of n-type nanocrystalline silicon thin films using magnetron sputtering and crystallization by adding antimony and thermal treatment is presented in this article. Firstly, a short overview about thin film deposition methods, along with the advantages and disadvantages of the magnetron sputtering, is provided. Then, the technique of adding metals for recrystallization of amorphous silicon is described, and the necessity of using antimony for obtaining n-type nanocrystalline silicon along with its characteristics is discussed. Next, the process of thin film deposition using magnetron sputtering and the production of n-type nanocrystalline silicon on a quartz substrate, by antimony induced crystallization, is explained. Subsequently, the characterization process and necessary measurements to confirm the crystallization of the nanocrystalline silicon layer and determine its crystalline properties are presented. For ease of electrical characterization, a simple n/p junction Schottky solar cell is fabricated using the produced nanocrystalline silicon layer on a p-type monocrystalline silicon wafer. In addition to nanocrystalline properties, the optical and electrical characteristics of this cell are also investigated. The measurements show that with the proposed method, a fine grains nanocrystalline silicon layer with an average grain size of 20 nm was formed in the &lt;111&gt; direction. J-V characteristic measurement shows the creation of a solar cell with conversion efficiency of 1.39%, open circuit voltage of 265mV and current density of 16.32mA/cm2. These results confirm that antimony can be used in the process of crystallizing amorphous thin film silicon obtained from magnetron sputtering and converting it into n-type nanocrystalline silicon.

Application of metal, metal‐oxide, and silicon‐oxide based intermediate reflective layers for current matching in autonomous high‐voltage multijunction photovoltaic devices

A logical next step for achieving a cost price reduction per Watt peak of photovoltaics (PV) is multijunction PV devices. In two-terminal multijunction PV devices, the photo-current generated in each subcell should be matched. Intermediate reflective layers (IRLs) are widely employed in multijunction devices to increase reflection at the interface between subcells to enhance current generation in the subcell(s) positioned before the IRL, in reference to the incident light. In this work, the results of over 65 multijunction devices are presented, in order to explore the effect of different current matching approaches. The influence of variations in absorber thickness as well as thickness variations of different IRLs based on silicon-oxide, various transparent conductive oxides (TCO), and metallic layers on all-silicon multijunction PV devices is studied. Specifically, hybrid, 2-terminal, monolithically integrated silicon heterojunction (SHJ) and thin film nanocrystalline silicon (nc-Si:H) and amorphous silicon (a-Si:H) tandem and triple junction devices are processed. Based on these experiments, certain design rules for optimal current matching operation in multijunction devices are formulated. Finally, taking these design rules into account, record all-silicon multijunction devices are processed. Conversion efficiencies close 15% and V oc ≈ 2 $$ {V}_{\mathrm{oc}}\approx 2 $$ V are demonstrated for triple junction SHJ/nc-Si:H/a-Si:H devices. Such conversion efficiencies for a wireless, high-voltage wafer-based all-silicon 2-terminal multijunction PV device opens the way for efficient autonomous solar-to-fuel synthesis systems as well as other wireless innovative approaches in which the multijunction solar cell is used not only as a photovoltaic current-voltage generator, but also as an ion-exchange membrane, electrochemical catalysts, and/or optical transmittance filter.

Hydrogen effect on structural and optical properties of in-situ fabricated nc-Si:H prepared by facing targets sputtering

We report high-quality hydrogenated nanocrystalline silicon (nc-Si:H) thin films were prepared by facing targets sputtering (FTS) in the environment of Ar and H2 mixture gases. By increasing hydrogen dilution (RH) of FTS deposition, the structural evolution of as-fabricated Si-based films was observed. Fourier infrared spectroscopy (FTIR) shows that decrease in bonded hydrogen (CH) concentration, especially that of (Si-H2)n with increasing RH, indicating that the H etching effect increased atomic density of these films, thus improving film quality. With the RH increased, the Raman spectra show that the morphological transition from amorphous to crystalline states. We further reveal correlations between the degree of structural order in the amorphous network and the RH by calculating experimental data from the Raman measurements. Moreover, as-fabricated nc-Si:H films show large bandgap and narrow band tail states with increasing RH, which allows potential applications in the window passivation layer for HIT solar cells and Si-based charge-coupled devices (CCD). This work offers a novel route to fabricate high-quality nc-Si:H films for optoelectronic applications.

Room temperature synthesized highly conducting B-doped nanocrystalline silicon thin films on flexible polymer substrates by ICP-CVD

Boron-doped nc-Si thin films were developed on inexpensive, optically-transparent, and flexible PET-substrates at ambient-temperature (∼30 °C) using (SiH4 + B2H6)-plasma, without additional H2-dilution, by optimizing the gas pressure in inductively-coupled low-pressure plasma-CVD. An amorphous and monohydride-Si dominated partially-nanocrystalline network was obtained at pressure, p ≤ 15 mTorr. At higher pressure, the local plasma heating on the polymer-substrate by the high-density plasma-precursors and over-abundant atomic-H causes plasma-induced nano-bends, which trigger the stress-induced-crystallization of the network on the flexible substrate even at ambient-temperature. Although, the enhanced atomic-H reactivity on the growing-surface at very-high pressures causes the formation of the polyhydride-dominated defective grain-boundary, which acts as the electron-trapping-center and eventually reduces the dark-conductivity. At an optimum pressure of ∼30 mTorr, the transport of ample SiH3-radicals and atomic-H from the plasma appears instrumental in producing the p-nc-Si thin film with high-crystallinity (∼77%) in columnar-like growth morphology and adequately wide optical bandgap (∼1.88 eV). Substitution of the Si-atoms, primarily residing in the lattice within the core of Si-nanocrystals, by the electrically-active four-fold-coordinated B-atoms (B4-) generates high-density of free charge-carriers and contributes to high electrical-conductivity (∼1 S cm−1) of the room-temperature grown p-nc-Si thin film on the flexible PET-substrate, which seems suitable for the fabrication of low-cost flexible-electronics, including Si solar-cells.

Intrinsic, P-doped and B-doped nanocrystalline silicon thin films grown at room temperature on flexible substrates for photovoltaic applications

Nanocrystalline silicon (nc-Si) thin films in its intrinsic (i-nc-Si), B-doped (p-nc-Si) and P-doped (n-nc-Si) configurations were developed on the flexible substrates at ambient temperature (∼30 °C), using no additional H2 dilution in planar inductively coupled plasma chemical vapour deposition (ICP-CVD) system. A superior crystallinity (∼81%) with electrical conductivity (σD ∼10-7 S cm−1) was achieved for the intrinsic Si thin film by the virtue of the presence of atomic-H in high density within ICP-CVD, which initiates nucleation even at room temperature on the flexible substrates. Substitution of boron (B) dopants at the crystalline Si lattice maintains a high crystallinity (∼80%) and results significantly high electrical conductivity (6 x10-1 S cm−1) in the p-nc-Si thin film. On the contrary, during the growth of n-nc-Si films, a substantial amount of phosphorous (P) dopants, residing at the interstitial position, results in a moderate crystallinity (∼73%) and relatively lesser conductivity (3 x10-1 S cm−1) than the p-nc-Si films. Finally, in the present work i-nc-Si, p-nc-Si and n-nc-Si thin films all are successfully prepared on the flexible substrates at room temperature, with ample crystallinity, wide optical band gap (∼1.9–1.80 eV) and significant electrical conductivity, which appear suitable for the low-cost fabrication of flexible p-i-n solar cells.

Effect of boron doping on structural, optical, and electrical properties of hydrogenated nanocrystalline silicon thin films grown by Cat-CVD method

Effect of boron doping on structural, optical, and electrical properties of hydrogenated nanocrystalline silicon thin films grown by Cat-CVD method

Exceptional thermoelectric power factors in hyperdoped, fully dehydrogenated nanocrystalline silicon thin films

Single-crystalline silicon is well known to be a poor thermoelectric material due to its high thermal conductivity. Most excellent research has focused on ways to decrease its thermal conductivity while retaining acceptably large power factors (PFs). Less effort has been spent to enhance the PF in poly- and nanocrystalline silicon, instead. Here, we show that in boron-hyperdoped nanocrystalline thin films, the PF may be increased up to 33 mW K−2 m−1 at 300 K when hydrogen embedded in the film during deposition is removed. The result makes nanocrystalline Si a realistic competitor of Bi2Te3 for low-temperature heat harvesting, also due to its greater geo-availability and lower cost.

Study of transition regime for amorphous to nano-crystalline silicon thin films using 27.12 MHz PECVD: Insight into plasma kinetics

In this article, we report the phase transition region of hydrogenated amorphous (a-Si:H) to nano-crystalline (nc-Si:H) silicon thin films deposited using 27.12 MHz assisted Plasma Enhanced Chemical vapor Deposition (PECVD) process with the approach of plasma diagnosis. This work presents for the first time a study of plasma characteristics using Impedance Analyser (V/I probe) at various applied power (4 W - 40 W), though till now this apparatus has been utilized only to analyse the applied delivered power during processing. On the basis of plasma diagnose, optimum bulk field (5 V/cm); sheath field (1376 V/cm) and minimum sheath width (7.4 x 10-4 cm) observed at 20 W power which provides a visible mark of transition from a-Si:H to nc-Si:H. On account of plasma properties, the deposition was carried out by considering the plasma-surface interaction during growth. The microstructure of the deposited films was characterized using Raman spectra, UV-Vis spectra and conductivity measurements and they were found to be well correlating with the evaluated plasma characteristics. In particular, it was found that at applied power near to the onset of transition regime i.e. at 10 W, preeminent properties of a-Si:H film was observed, predominantly in terms of highest photosensitivity (7.2x103), low photo-degradation and high deposition rate (~1.39 Å/s). On the other hand, volume fraction of crystallites (24 %), wider band gap (2.0 eV) and no photo-degradation observed for the film deposited at 20 W applied power which signifies the existence of crystallites in an amorphous matrix. Copyright © 2017 VBRI Press.

Supporting plasma processes for fabrication of n-doped nano-crystalline silicon thin film on low-cost glass substrates

Nano-crystalline silicon is an excellent material for applications in the optoelectronics industry. This intermediate material combines both the advantages of amorphous and crystalline silicon. However, the typical fabrication process of nano-crystalline silicon previously required high-quality substrates such as quartz or silicon wafers, which limited its potential applications. Recently, plasma treatments have been recognized as the most efficient and customizable methods for transforming materials. In this study, corona plasma was used to treat the low-cost glass substrates to improve their adhesion to silicon thin films. It allowed the film to become more uniform with a surface roughness of less than 10% at the thickness of about 1 μm. The conventional thermal annealing process was replaced by a high-power hydrogen plasma process, which does not cause harmful effects on the glass substrates and stimulates the amorphous-crystalline phase transition. The increasing of the crystalline fraction, which is known as the order of arrangement of silicon atoms network, affects the doped concentration as well as the electrical properties of the nc-Si:H thin films. The resulting n-doped nano-crystalline silicon thin film has a crystalline fraction of 32.8%, corresponding to a sheet resistance of 104 Ω/square.

The effect of ultrasmall grain sizes on the thermal conductivity of nanocrystalline silicon thin films

Nanocrystallization has been an important approach for reducing thermal conductivity in thermoelectric materials due to limits on phonon mean-free path imposed by the characteristic structural size. We report on thermal conductivity as low as 0.3 Wm−1K−1 of nanocrystalline silicon thin films prepared by plasma-enhanced chemical-vapor deposition as grain size is reduced to 2.8 nm by controlling hydrogen dilution of silane gas during growth. A multilayered film composed by alternating growth conditions, with layer thicknesses of 3.6 nm, is measured to have a thermal conductivity 30% and 15% lower than its two constituents. Our quantitative analysis attributes the strong reduction of thermal conductivity with decreasing grain size to the magnifying effect of porosity which occurs concomitantly due to increased mass density fluctuations. Our results demonstrate that ultrasmall grain sizes, multilayering, and porosity, all at a similar nanometer-size scale, may be a promising way to engineer thermoelectric materials.

Role of Deposition Pressure on Properties of Phosphorus Doped Hydrogenated Nano-Crystalline Silicon (nc-Si:H) Thin Films Prepared by the Cat-CVD Method

Objective: Phosphorus doped hydrogenated nano-crystalline silicon (nc-Si:H) thin films were synthesized by catalytic chemical vapor deposition (Cat-CVD) method. Methods: The effect of deposition pressure on opto-electronic and structural properties was studied using various analysis techniques such as low angle XRD analysis, FTIR spectroscopy, Raman spectroscopy, UV-Visible spectroscopy, dark conductivity, etc. Results: From low angle XRD and Raman spectroscopy analysis, it is observed that an increase in deposition pressure causes Si:H films to transform and transit from amorphous to the crystalline phase. At optimized deposition pressure (300 mTorr), phosphorous doped nc- Si:H films having a crystallite size of ∼29 nm and crystalline volume fraction of ∼58% along with high deposition rate (∼29.7 Å/s) have been obtained. The band gap was found to be ∼1.98 eV and hydrogen content was as low as (∼1.72 at. %) for these films. Conclusion: The deposited films can be useful as an n-type layer for Si:H based p-i-n, tandem and c-Si hetero-junction solar cells.

Nanocrystalline silicon thin film growth and application for silicon heterojunction solar cells: a short review.

Doped nanocrystalline silicon (nc-Si:H) thin films offer improved carrier transport characteristics and reduced parasitic absorption compared to amorphous silicon (a-Si:H) films for silicon heterojunction (SHJ) solar cell application. In this article, we review the growth conditions of nc-Si:H thin films as the carrier-selective layers for SHJ solar cells. Surface and growth zone models are analysed at different stages of incubation, nucleation, and growth of the silicon nanocrystallites within the hydrogenated amorphous silicon matrix. The recent developments in the implementation of nc-Si:H films and oxygen-alloyed nc-SiOx:H films for SHJ cells are highlighted. Furthermore, hydrogen and carbon dioxide plasma treatments are emphasised as the critical process modification steps for augmenting the nc-Si:H films' optoelectronic properties to enhance the SHJ device performance with better carrier-selective interfaces.

Design and optimization of passivation layers and emitter layers in silicon heterojunction solar cells

&lt;sec&gt;Silicon heterojunction (SHJ) solar cells have attracted much attention in the international photovoltaic market due to their high efficiencies and low costs. The quality of amorphous silicon/crystalline silicon (a-Si:H/c-Si) interfaces of SHJ solar cells has a key influence on the device performance. Therefore, the carrier recombination rate of a-Si:H/c-Si interface needs to be effectively controlled. In addition, as the important component of SHJ solar cells, the p-type emitter must meet the requirements for high conductivity, high light transmittance, and energy band matching with c-Si. The research contents and the relevant achievements of this paper include the following aspects. &lt;/sec&gt;&lt;sec&gt;Firstly, in order to reduce the surface defects and realize the energy band alignment of a-Si:H/c-Si interface, the effect of passivation layer on passivation effect is studied. An ultra-thin buffer layer deposited by a low power and a high hydrogen dilution ratio is inserted between the conventional passivation layer and c-Si to improve the passivation effect and broaden the process window of passivation layer. The effects of the buffer layer thickness and hydrogen dilution ratio on passivation quality are further studied, and the best experimental conditions of buffer layer are obtained. The experimental results show that the sample with double-layered passivation layer is more stable than the conventional passivation layer. The minority carrier lifetime of the sample with single conventional passivation layer is 3.8 ms and the &lt;i&gt;iV&lt;/i&gt;&lt;sub&gt;OC&lt;/sub&gt; is 712 mV, while the minority carrier lifetime of the sample with double-layered passivation layer is 4.197 ms and the &lt;i&gt;iV&lt;/i&gt;&lt;sub&gt;OC&lt;/sub&gt; is 726 mV.&lt;/sec&gt;&lt;sec&gt;Secondly, for the p-type emitters of silicon heterojunction solar cells, the effects of doping level on the photoelectric properties of p-type hydrogenated nanocrystalline silicon (nc-Si:H) thin films are studied. On this basis, the p&lt;sup&gt;++&lt;/sup&gt;-nc-Si:H/p-nc-Si:H double-layer emitter with wide band gap and high conductivity is designed and fabricated. By analyzing the optical and electrical properties of different emitters, it is found that p-nc-Si:H has good electrical and optical properties. Owing to the high doping efficiency of nc-Si, a small amount of doping can obtain high conductivity. Lightly doped p-nc-Si:H provides a better contact with the passivation layer, while heavily doped p&lt;sup&gt;++&lt;/sup&gt;-nc-Si:H can not only provide enough built-in electric field, but also improve the contact characteristics of p/ITO, thus enhancing the output characteristics of the cell. At the same time, the deposition of p-nc-Si:H layer with high hydrogen dilution ratio can also implement the hydrogen plasma treatment on the passivation layer, the reduction of the dangling bonds on the surface of the c-Si, the enhancement of the chemical passivation effect, and thus improving the open circuit voltage of the cell. &lt;/sec&gt;&lt;sec&gt;Finally, a silicon heterojunction solar cell with an efficiency of 20.96% is obtained based on the commercial czochralski silicon wafer, with an open circuit voltage of 710 mV, a short circuit current density of 39.88 mA/cm&lt;sup&gt;2&lt;/sup&gt; and filling factor of 74.02%.&lt;/sec&gt;

Crystallite distribution analysis based on hydrogen content in thin-film nanocrystalline silicon solar cells by atom probe tomography

The three-dimensional (3D) distribution of nanosized silicon (Si) crystallites within a hydrogenated nanocrystalline Si (nc-Si:H) material is examined by laser-assisted atom probe tomography (APT). The amorphous and crystalline phases in nc-Si:H are distinguished by obtaining the 3D density distribution of H atoms, because the former contains a high H density. The H content in the amorphous phase is estimated to be approximately 15 at% by APT, which is consistent with that obtained by infrared spectroscopy. Thus, the 3D analysis of H distribution via APT is a powerful method to visualize the real shape of nanosized crystallites within nc-Si:H materials.

Fabrication of Nanocrystalline Silicon Thin Films Utilized for Optoelectronic Devices Prepared by Thermal Vacuum Evaporation.

Metal-induced crystallization of amorphous silicon is a promising technique for developing high-quality and cheap optoelectronic devices. Many attempts tried to enhance the crystal growth of polycrystalline silicon via aluminum-induced crystallization at different annealing times and temperatures. In this research, thin films of aluminum/silicon (Al/Si) and aluminum/silicon/tin (Al/Si/Sn) layers were fabricated using the thermal evaporation technique with a designed wire tungsten boat. MIC of a:Si was detected at annealing temperature of 500 °C using X-ray diffraction, Raman spectroscopy, and field emission scanning electron microscopy. The crystallinity of the films is enhanced by increasing the annealing time. In the three-layer thin films, MIC occurs because of the existence of both Al and Sn metals forming highly oriented (111) silicon. Nanocrystalline silicon with dimensions ranged from 5 to 300 nm is produced depending on the structure and time duration. Low surface reflection and the variation of the optical energy gap were detected using UV–vis spectroscopy. Higher conductivities of Al/Si/Sn films than Al/Si films were observed because of the presence of both metals. Highly rectifying ideal diode manufactured from Al/Si/Sn on the FTO layer annealed for 24 h indicates that this device has a great opportunity for the optoelectronic device applications.