Hydrogenated Amorphous Silicon Thin Film Research Articles

Crystallization of Hydrogenated Amorphous Silicon Thin Films Using Combined Continuous Wave Laser and Thermal Annealing

Crystallization of Hydrogenated Amorphous Silicon Thin Films Using Combined Continuous Wave Laser and Thermal Annealing

Fine-Tuning Intrinsic and Doped Hydrogenated Amorphous Silicon Thin-Film Anodes Deposited by PECVD to Enhance Capacity and Stability in Lithium-Ion Batteries.

Silicon is a promising alternative to graphite as an anode material in lithium-ion batteries, thanks to its high theoretical lithium storage capacity. Despite these high expectations, silicon anodes still face significant challenges, such as premature battery failure caused by huge volume changes during charge-discharge processes. To solve this drawback, using amorphous silicon as a thin film offers several advantages: its amorphous nature allows for better stress mitigation and it can be directly grown on current collectors for material savings and improved Li-ion diffusion. Furthermore, its conductivity is easily increased through doping during its growth. In this work, we focused on a comprehensive study of the influence of both electrical and structural properties of intrinsic and doped hydrogenated amorphous silicon (aSi:H) thin-film anodes on the specific capacity and stability of lithium-ion batteries. This study allows us to establish that hydrogen distribution in the aSi:H material plays a pivotal role in enhancing battery capacity and longevity, possibly masking the significance of the conductivity in the case of doped electrodes. Our findings show that we were able to achieve high initial specific capacities (3070 mAhg-1 at the 10th cycle), which can be retained at values higher than those of graphite for a significant number of cycles (>120 cycles), depending on the structural properties of the aSi:H films. To our knowledge, this is the first comprehensive study of the influence of these properties of thin films with different doping levels and hydrogen distributions on their optimization and use as anodes in lithium-ion batteries.

Annealing Temperature Effect on Bismuth Induced Crystallization of Hydrogenated Amorphous Silicon Thin Films

Annealing Temperature Effect on Bismuth Induced Crystallization of Hydrogenated Amorphous Silicon Thin Films

Observation of electrically detected electron nuclear double resonance in amorphous hydrogenated silicon films

We report on the electrical detection of electron nuclear double resonance (EDENDOR) through spin-dependent tunneling transport in an amorphous hydrogenated silicon thin film. EDENDOR offers a many orders of magnitude improvement over classical ENDOR and is exclusively sensitive to paramagnetic defects involved in electronic transport. We observe hyperfine interactions with 1H nuclei very close to silicon dangling bond defects. These observations substantially extend recent EDENDOR observations involving silicon vacancy defects and 14N hyperfine interactions with fairly distant nitrogen atoms in 4H-SiC bipolar junction transistors. We have improved the detection scheme utilized in the earlier study by combining magnetic field modulation with RF amplitude modulation; this combination significantly improves the operation of the automatic power leveling scheme and the overall sensitivity.

Long-Term Behavior of Hydrogenated Amorphous Silicon Thin-Film Transistors Covered With Color Filters for Use in Optical Sensors

This work investigates the long-term behavior of photo thin-film transistors (TFTs) that are covered with color filters and based on hydrogenated amorphous silicon (a-Si:H) technology. Based on the electrical characteristics and the optical responses of these TFTs as measured under different stress conditions, a new method for driving a photo TFT with a negative gate-source voltage is proposed to suppress the degradation of the photocurrent. The effectiveness of the newly proposed method is verified using our previously developed white-light photocurrent gating (WPCG) structure, the measurement of photocurrents, and the established models of red, green, and blue photo TFTs. An accelerated lifetime test of the fabricated circuit was carried out at 70 °C and under the illumination of ambient light for 504 hours, demonstrating that the proposed method improves the long-term reliability of optical sensors.

Optical Properties of Hydrogenated Amorphous Silicon Thin-Film Transistor-Based Optical Pixel Sensor in Three Primary Colors

This work investigates the characteristics and optical responses of photo thin-film transistors (TFTs) that are covered with color filters in the three primary colors. The transmission rates of the color filters under the illumination with various wavelengths are presented as a reference for the integration of photo TFTs with conventional color filters. Measurements are made on previously developed white-light photocurrent gating (WPCG) structures with compensating photo TFTs with different aspect ratios to examine the driving capabilities of three photo TFTs. Favorable values of parameters of the applied WPCG structures that yield similar responses are established from the measured outputs of the structures, benefiting the integration of optical input functions with the three primary color optical input signals for large TFT-LCD panels.

Performance of p-i-n Hydrogenated Amorphous Silicon Thin Film Solar Cells Device

Performance of p-i-n Hydrogenated Amorphous Silicon Thin Film Solar Cells Device

A Hydrogenated Amorphous Silicon Thin-Film Transistor Optical Pixel Sensor for Ameliorating Influences of Ambient Light and Reflected Light

This paper proposes a hydrogenated amorphous silicon thin-film transistorbased (a-Si:H TFT) optical pixel sensor. The proposed optical sensor compensates for variations of ambient light using photo TFTs that incorporate with three primary color filters, and a designed active load is utilized to release the photocurrent from the noise of reflected light. Measurement results reveal that the proposed sensor suppresses the effect of ambient light within the intensity of 12 560 lux and does not react to a blue light with an intensity of 588 lux, proving that the proposed optical sensor remains highly reliable under heavy ambient light and avoids the interference of reflected light.

Effect of Mechanical Strain on Hydrogenated Amorphous Silicon Thin-Film Transistors and Compensation Circuits on Flexible Substrates

Hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) compensation pixel circuits were fabricated on polyethylene naphthalate substrates at amax-imumtemperature of 170 °C. The typical a-Si:H TFTs showed a field-effect mobility ( $\mu _{\text {FE}}$ ) of 0.8–1.1 cm $^{2}$ /Vs, a threshold voltage ( ${V}_{T}$ ) of 2–3.3 V, a subthreshold swing (SS) of ~0.65 V/decade, and an ON/OFF current ratio of $10^{7}$ – $10^{8}$ . Under DC gate-bias stress without compensation, the TFT drive current decreased by ~50% withoutmechanical strain and ~60% with applied tensile strain. The TFT circuits effectively compensated for the change in the TFT drive current to within 10% of the original drive current value under mechanically strained and unstrained states. The orientation of the TFT within the circuit was found to affect the circuit compensation; TFTs having a channel length perpendicular to the mechanical strain were found to have a 50% higher threshold voltage shift ( $\Delta {V}_{T}$ ) compared to devices parallel to the applied strain.

Optical Pixel Sensor of Hydrogenated Amorphous Silicon Thin-Film Transistor Free of Variations in Ambient Illumination

This paper presents a primary color optical pixel sensor circuit that utilizes hydrogenated amorphous silicon thin-film transistors (TFTs). To minimize the effect of ambient light on the sensing result of optical sensor circuit, the proposed sensor circuit combines photo TFTs with color filters to sense a primary color optical input signal. A readout circuit, which also uses thin-film transistors, is integrated into the sensor circuit for sampling the stored charges in the pixel sensor circuit. Measurements demonstrate that the signal-to-noise ratio of the proposed sensor circuit is unaffected by ambient light under illumination up to 12 000 lux by white LEDs. Thus, the proposed optical pixel sensor circuit is suitable for receiving primary color optical input signals in large TFT-LCD panels.

Aluminum-Induced Crystallization of Hydrogenated Amorphous Silicon Thin Films With Assistance of Electric Field for Solar Photovoltaic Applications

In this work, the aluminum-induced crystallization of hydrogenated amorphous silicon (a-Si:H) has been investigated. Specifically, constant temperature and voltage were applied on a-Si:H films covered with a very thin layer of pure aluminum. Each sample was subjected to annealing for 15 minutes while connected to an external electrical power. Nine different treatments of annealing temperatures and voltages were included in this study. The levels of applied voltages were 0 V, 2 V, or 20 V, and the levels of annealing temperatures were 200 $^{\circ}{\hbox{C}}$ , 250 $^{\circ}{\hbox{C}}$ , and 300 $^{\circ}{\hbox{C}}$ . The electrical, morphological, and structural properties of the treated a-Si:H layer were studied. The results of energy dispersive X-ray spectroscopy showed a diffusion of aluminum atoms inside the a-Si:H layer. While, X-ray diffraction revealed that the crystallization depends on both the annealing temperature and the external voltage. Moreover, the obtained results showed that the electrical resistivity decreases considerably, the carrier concentration deceases slowly, while the Hall mobility increases sharply with increasing the annealing temperature and the applied voltage.

High Quality Hydrogenated Amorphous Silicon Thin Films with Enhanced Growth Rates for Surface Passivation in an Al2O3 Based ICP Reactor

Plasma processing of materials in low frequency inductively coupled plasma (LF-ICP) reactors has limitations involving the presence of contaminant species found in the discharge. It has been shown in previous work through optical emission spectroscopy that a main source of contaminants were oxygen related species which were not part of the feedstock recipe. In this work, amorphous silicon thin films were grown on silicon substrates with a LF-ICP reactor. The dielectric top lid plays an important role in the reduction of oxygen species detected in the thin films. It was postulated that the source of the contaminants came from sputtering of the lids. The replacement of the conventional quartz (SiO2) lid with that of alumina (Al2O3) reduced the oxygen species present in the resulting discharge, which is often a source of contamination in the resulting thin films, impinging the passivation grade of the resulting films. The modified reactor configuration also resulted in increased hydrogenation and deposition rate of the thin films. The results show that alumina lids serve as a promising alternative in replacing the conventional quartz lids in LF-ICP reactors for materials processing, resulting in efficient power transfer to the plasma and films which are rid of contaminant species.

Role of SiNx Barrier Layer on the Performances of Polyimide Ga₂O₃-doped ZnO p-i-n Hydrogenated Amorphous Silicon Thin Film Solar Cells.

In this study, silicon nitride (SiNx) thin films were deposited on polyimide (PI) substrates as barrier layers by a plasma enhanced chemical vapor deposition (PECVD) system. The gallium-doped zinc oxide (GZO) thin films were deposited on PI and SiNx/PI substrates at room temperature (RT), 100 and 200 °C by radio frequency (RF) magnetron sputtering. The thicknesses of the GZO and SiNx thin films were controlled at around 160 ± 12 nm and 150 ± 10 nm, respectively. The optimal deposition parameters for the SiNx thin films were a working pressure of 800 × 10−3 Torr, a deposition power of 20 W, a deposition temperature of 200 °C, and gas flowing rates of SiH4 = 20 sccm and NH3 = 210 sccm, respectively. For the GZO/PI and GZO-SiNx/PI structures we had found that the GZO thin films deposited at 100 and 200 °C had higher crystallinity, higher electron mobility, larger carrier concentration, smaller resistivity, and higher optical transmittance ratio. For that, the GZO thin films deposited at 100 and 200 °C on PI and SiNx/PI substrates with thickness of ~000 nm were used to fabricate p-i-n hydrogenated amorphous silicon (α-Si) thin film solar cells. 0.5% HCl solution was used to etch the surfaces of the GZO/PI and GZO-SiNx/PI substrates. Finally, PECVD system was used to deposit α-Si thin film onto the etched surfaces of the GZO/PI and GZO-SiNx/PI substrates to fabricate α-Si thin film solar cells, and the solar cells’ properties were also investigated. We had found that substrates to get the optimally solar cells’ efficiency were 200 °C-deposited GZO-SiNx/PI.

Plasmonic Modes in Molybdenum Ultra-thin Films Suitable for Hydrogenated Amorphous Silicon Thin Film Solar Cells

We have recently demonstrated that molybdenum ultra-thin films interposed between hydrogenated amorphous silicon (a-Si:H) and SnO2:F transparent conductive oxide (TCO) in thin film a-Si:H solar cells show light trapping effects which enhance the solar cells performances. The effect of this improvement may be attributed to surface plasmon polariton (SPP) modes excited at the molybdenum interface by the solar radiation. In this paper we show direct evidence of such SPP modes in the case of the molybdenum/air interface by using the attenuated total reflection (ATR) technique, pioneered by Kretschmann, and we evaluate the dielectric constant of molybdenum at 660nm.

Compact Decoder-Type Gate Driver Circuits with Hydrogenated Amorphous Silicon Thin Film Transistors for Active Matrix Displays

In this paper, we propose an integrated hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) gate driver circuit with parallely connected TFTs to resolve problems of the large circuit area and large number of input signals which are founded in the previously reported decoder-type and demultiplexer-type integrated gate drivers. The proposed gate driver can alleviate the demerits of previous gate drivers while maintaining their advantages: reduction of the threshold voltage (Vth) shift of the a-Si:H TFTs with an AC-driving structure and provide a stable low-impedance output. The key idea is to construct a novel decoder based on parallely connected TFTs instead of serially connected ones that are very common for decoders. The simulation results show that the rising time and falling time are 1.27 and 1.63 µs respectively with -5 to 30 V output voltage swing which are suitable for high resolution active-matrix displays.

Effects of Photon Energy Spectrum on the Photocurrent of Hydrogenated Amorphous Silicon Thin Film Transistor by Using Frequency Filters

Frequency filters with various filtering wavelengths were used in the photoelectric characterization of hydrogenated amorphous silicon thin film transistor (a-Si:H TFT) and the experimental results were described and analyzed in terms of the photon energy spectral characteristics calculated from the integration of the photon energy and the spectral intensity of transmitted backlight through the filters at each wavelength. From the comparison of the photocurrents and the calculated photon energy spectrums for the filtered ranges of wavelength, it was possible to conclude that the photocurrents are closely related to the photon energy spectrums of the backlight.

表面粗糙氢化非晶硅薄膜光学常量的确定

表面粗糙氢化非晶硅薄膜光学常量的确定

氢化非晶硅薄膜的光谱椭偏研究

氢化非晶硅薄膜的光谱椭偏研究

Interphase chemistry of Si electrodes used as anodes in Li-ion batteries

The effect of the Si electrode morphology (amorphous hydrogenated silicon thin films – a-Si:H as a model electrode and Si nanowires – SiNWs electrode) on the interphase chemistry was thoroughly investigated by the surface science techniques: X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS analysis shows a strong attenuation and positive shift of the Si 2p peaks after a complete charge/discharge performed in PC- and EC:DMC-based electrolytes for both electrodes (a-Si:H and SiNW), confirming a formation of a passive film (called solid electrolyte interphase – SEI layer). As evidenced from the XPS analysis performed on the model electrode, the thicker SEI layer was formed after cycling in PC-based electrolyte as compared to EC:DMC electrolyte. XPS and ToF-SIMS investigations reveal the presence of organic carbonate species on the outer surface and inorganic salt decomposition species in the inner part of the SEI layer. Significant modification of the surface morphology for the both electrodes and a full surface coverage by the SEI layer was confirmed by the scanning electron microscopy (SEM) analysis.

Efficient Hydrogenated Amorphous Silicon Thin-Film Solar Cells Using Zinc Oxide Deposited by Atomic Layer Deposition as a Protective Interfacial Layer

A single zinc oxide (ZnO) layer deposited by atomic layer deposition (ALD) was employed as a buffer layer on textured fluorine-doped tin oxide (FTO) glass in p-i-n-type hydrogenated amorphous silicon solar cells (a-Si:H SCs). ZnO was deposited between FTO glass and a p-type a-Si:H layer. The device with a 2 nm thick ZnO buffer layer deposition showed the highest cell efficiency as well as increased current density, showing considerable improvement in efficiency. This improvement was attributed to the protection against H2 plasma damage during plasma-enhanced chemical vapor deposition, which was confirmed by electrical impedance, conductivity, and optical transmittance measurements.