Hydrogenated Amorphous Silicon Thin Film Research Articles

Hydrogenated Amorphous Silicon Thin Film Solar Cells Using a Hybrid Buffer Layer of Gold Nanoparticle and Tungsten Oxide Thin Film

A double layer of gold nano particles (Au-NPs) and amorphous tungsten oxide (a-WO3) was employed as a buffer layer on textured fluorine-tin oxide (FTO) glass in pin-type hydrogenated amorphous silicon solar cells (a-Si:H SCs). Au-NPs of ∼10 nm size were spin coated and a-WO3 layer was thermally evaporated between Au-NPs on a FTO glass and hydrogenated amorphous p-type Si layer. a-Si:H SCs with a double buffer layer showed higher efficiency of 7% improvement, 8.059% from a value of 7.530%, and increased current density of 8.3% improvement, 14.212 mA/cm2 from a value of 13.120 mA/cm2, originating from the enhancement of electrical interface contact and bandgap alignment, as well as the slight absorption and surface plasmon resonance effect due to Au-NPs on textured FTO glass.

Design and Simulation of Infrared Absorption Based on Hydrogenated Amorphous Silicon Thin Film

Hydrogenated amorphous silicon (a-Si:H) thin film has nowadays attracted much attention in a wide range of electronic applications as in image sensors and in solar cells because of its merits and compatibility with semiconductor technology. In this paper, the background of a-Si:H thin film technology and microbolometer technology has been described in details. According to optical admittance matrix method, the multilayer film system based on a-Si:H thin film was simulated by MatLab software, mainly for the simulation of infrared absorption layers and the simulation of microbolometer. The results show that the combination of TiN film and a-Si:H film is suitable for the design of microbolometer within the middle and far infrared wave band (8-14µm), and the infrared absorptivity of the modified microbolometer can reach over 90%.

Effect of Nitrogen Doping on the Structure and Optical Properties of N-Type Hydrogenated Amorphous Silicon Thin Films

Hydrogenated amorphous silicon (a-Si:H) thin films doped with both Phosphor and Nitrogen are deposited by ratio frequency plasma enhanced chemical vapor deposition (PECVD). The effect of gas flow rate of ammonia (FrNH3) on the composition, microstructure and optical properties of the films has been investigated by X-ray photoelectron spectroscopy, Raman spectroscopy and ellipsometric spectra, respectively. The results show that with the increase of FrNH3, Si-N bonds appear while the short-range order deteriorate in the films. Besides, the optical properties of N-doped n-type a-Si:H thin films can be easily controlled in a PECVD system.

Asymmetric Electrical Properties of Half Corbino Hydrogenated Amorphous Silicon Thin-Film Transistor and Its Applications to Flat Panel Displays

The half-Corbino hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) were fabricated with a five-photomask process used in the processing of the active matrix liquid-crystal displays (AM-LCD). We showed that the a-Si:H half-Corbino TFTs have the asymmetric electrical characteristics under different drain-bias conditions. In comparison to half-Corbino TFT with unpatterned gate electrode, the device parasitic capacitance can be significantly reduced by patterning the gate electrode for same device dimension, while the sub-threshold swing and threshold voltage remain identical for same bias condition. The OFF-current remains below 0.1 pA for all device configurations. Finally, we discuss their potential applications as a driving or switching TFT to various flat panel displays.

Asymmetric Electrical Properties of Half Corbino Hydrogenated Amorphous Silicon Thin-Film Transistor and Its Applications to Flat Panel Displays

The half-Corbino hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) were fabricated with a five-photomask process used in the processing of the active matrix liquid-crystal displays (AM-LCD). We showed that the a-Si:H half-Corbino TFTs have the asymmetric electrical characteristics under different drain-bias conditions. In comparison to half-Corbino TFT with unpatterned gate electrode, the device parasitic capacitance can be significantly reduced by patterning the gate electrode for same device dimension, while the sub-threshold swing and threshold voltage remain identical for same bias condition. The OFF-current remains below 0.1 pA for all device configurations. Finally, we discuss their potential applications as a driving or switching TFT to various flat panel displays.

Formation of Nano-Crystalline Phase in Hydrogenated Amorphous Silicon Thin Film by Plasma Focus Ion Beam Irradiation

A 3.3 kJ Mather type dense plasma focus device is used to generate a pulsed argon ion beam of 100 KeV in this work. Hydrogenated amorphous silicon (a-Si:H) film prepared by plasma enhanced chemical vapor deposition (PECVD) on c-Si substrate was irradiated with the argon ion beam produced by this dense plasma focus device. The effects of exposure to a single, 5 and 10 shots of dense plasma focus argon ion beam irradiation on the surface morphology, crystallinity and chemical bonding properties of the a-Si:H films were studied using Field Emission Scanning Electron Microscope (FESEM), X-ray Diffraction (XRD), Raman scattering and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Formation of nano-crystalline silicon phase along with increase in structural order and hydrogen content in the film structure has been observed when the a-Si:H film was irradiated with a single shot of dense plasma focus argon ion beam. Exposure to 5 and 10 shots of the dense plasma focus argon ion beam irradiation reduced the hydrogen content resulting in a decrease in crystallinity and structural order in the film structure.

Effect of B Boping Concentration on the Properties of P-Type Hydrogenated Amorphous Silicon Thin Films

P-type hydrogenated amorphous silicon films were deposited on float glass substrates by plasma enhanced chemical vapor deposition (PECVD). The effect of B doping concentration on the properties of the films was studied. The structure of the films was investigated by X-ray diffraction (XRD). The transmittance of the films was measured using an UV–Vis–NIR spectrophotometer in the wavelength range 200–2600nm.The film thickness was fitted by NKD-7000W optical thin film analysis system. The optical band gap of the films was obtained by the Tauc method. The conductivity of the films was tested by Electrometer Keithley 6517B. The results show that the optical band gap of the films changes from 1.93 eV to 1.65eV with the increase of B doping concentration, the highest conductivity of the film doped with 1.86% B2H6is 7.82 × 10-4S/cm.

Electronic Transport Properties of Hydrogenated Amorphous Silicon Thin Films Deposited on Plastic Substrates

Aiming for potential application in flexible solar cells, electronic transport properties are studied for hydrogenated amorphous silicon thin films on plastic substrates. Intrinsic hydrogenated amorphous silicon layers are deposited on Kapton and Upilex-s polyimide substrates at temperatures of 100°C and 180°C by plasma enhanced chemical vapor deposition (PECVD) system. Layers on 75μm and 125 thick Kapton and on 125 Upilex-s substrates are characterized by dark conductivity and activation energy measurements. It can be concluded that the intrinsic layer on 125μm thick Kapton and Upilex-s plastic both have favorable electrical properties and therefore could be employed as substrate material for flexible solar cells.

Raman characterization of the structural evolution in amorphous and partially nanocrystalline hydrogenated silicon thin films prepared by PECVD

AbstractHydrogenated silicon (Si:H) thin films were obtained by plasma‐enhanced chemical vapor deposition (PECVD). Raman spectroscopy was used to investigate the structural evolution in phosphor‐doped n‐type amorphous hydrogenated silicon thin films, which were prepared under different substrate temperatures and gas pressures. Meanwhile, the effect of nitrogen doping on the structure of P‐doped thin films was also investigated by Raman spectroscopy. Moreover, the transition from the amorphous state to the nanocrystalline state of undoped Si:H films deposited through low argon dilution was studied by Raman spectroscopy, X‐ray diffraction, and transmission electron microscopy. The results show that Raman spectroscopy can sensitively detect the structural evolution in hydrogenated silicon thin films deposited under different conditions in a PECVD system. Copyright © 2010 John Wiley & Sons, Ltd.

Driving Method for Compensating Reliability Problem of Hydrogenated Amorphous Silicon Thin Film Transistors and Image Sticking Phenomenon in Active Matrix Organic Light-Emitting Diode Displays

Driving Method for Compensating Reliability Problem of Hydrogenated Amorphous Silicon Thin Film Transistors and Image Sticking Phenomenon in Active Matrix Organic Light-Emitting Diode Displays

Driving Method for Compensating Reliability Problem of Hydrogenated Amorphous Silicon Thin Film Transistors and Image Sticking Phenomenon in Active Matrix Organic Light-Emitting Diode Displays

In this paper, we propose a driving method for compensating the electrical instability of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) and the luminance degradation of organic light-emitting diode (OLED) devices for large active matrix OLED (AMOLED) displays. The proposed driving method senses the electrical characteristics of a-Si:H TFTs and OLEDs using current integrators and compensates them by an external compensation method. Threshold voltage shift is controlled a using negative bias voltage. After applying the proposed driving method, the measured error of the maximum emission current ranges from -1.23 to +1.59 least significant bit (LSB) of a 10-bit gray scale under the threshold voltage shift ranging from -0.16 to 0.17 V.

Hydrogenated Amorphous Silicon Thin-Film Disk Resonators

Microelectromechanical (MEMS) structures consisting of surface micromachined disk resonators of phosphorous- doped hydrogenated amorphous silicon (n-a-Si:H) deposited by radiofrequency plasma enhanced chemical vapour deposition (RF-PECVD) were fabricated and characterized. Quality factors up to 104 in vacuum were measured for disk resonators operating at frequencies between 0.1 and 10MHz. The metallized structures were actuated with electrostatic force by radially placed electrodes. Finite element simulations were used to identify the type of vibrational modes present and show good agreement with measured values. Resonator geometry and ambient pressure were varied to attain a generalized understanding of the RF performance. Higher harmonic modes show increasing quality factors which bears great potential when designing sensors for operation in dissipative media.

A study of optical absorption in amorphous hydrogenated silicon thin films of varied thickness

We report results obtained from optical absorption studies carried out on amorphous silicon thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) from silane plasma. The influence of the film thickness was studied on the two series of samples deposited from undiluted silane and under moderate hydrogen dilution of silane. Spectral refractive indices and absorption coefficients were determined from transmittance spectra. The spectral absorption coefficients were used to determine the Tauc optical band-gap energies E g, the B factors of the Tauc plots, the iso-energy values E 04 (energy at which the absorption coefficient is equal to 10 4 cm −1). The results were correlated with volume fractions of the amorphous phase and voids and with the film thickness.

Dual-Gate Characteristics of Amorphous $ \hbox{InGaZnO}_{4}$ Thin-Film Transistors as Compared to Those of Hydrogenated Amorphous Silicon Thin-Film Transistors

We compare the mutual interactions between the top-and bottom-gate fields in a dual-gate structure for amorphous InGaZnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> (a-IGZO) and hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs). We find that a-IGZO TFTs show more significant mutual interactions than a-Si:H TFTs. By using a wide variety of a-IGZO TFTs with varying thicknesses of a-IGZO and gate-insulator layers, we have investigated, on the basis of a conventional fully depleted n-channel silicon-on-insulator model, the mechanism behind parallel shifts in transfer characteristics caused by negative top-gate voltages. Experimental results, even for relatively thick (over 150 nm) a-IGZO layers, are in good agreement with the fully depleted model. This fact may be related to the nonexistence of hole accumulation in a-IGZO, which is an intrinsic property of oxide semiconductors. In contrast, for the a-Si:H TFTs, there is a considerable discrepancy between the experimental results and the model. This discrepancy probably results from the limited penetration of band bending into the a-Si:H layer, as well as from the hole accumulation at the top interface. Such analysis of a-IGZO TFTs is of practical importance in device applications because many issues related to the fabrication and structure of a-IGZO TFTs may be resolved with a better understanding of dual-gate performance.

Hydrogenated Amorphous Silicon Thin Films as Passivation Layers Deposited by Microwave Remote-PECVD for Heterojunction Solar Cells

An intrinsic silicon thin film passivation layer is deposited by the microwave remote-plasma enhanced chemical vapor deposition at temperature of 175 C and various gas ratios for solar cell applications. The good quality amorphous silicon films were formed at silane (SiH4) gas flow rates above 15 sccm. The highest effective carrier lifetime was obtained at the SiH4 flow rate of 20 sccm and the value was about 3 times higher compared with the bulk lifetime of 5.6 μs at a fixed injection level of ∆n = 5×10 cm. An annealing treatment was performed and the carrier life times were increased approximately 5 times compared with the bulk lifetime. The optimal annealing temperature and time were obtained at 250 C and 60 sec respectively. This indicates that the combination of the deposition of an amorphous thin film at a low temperature and the annealing treatment contributes to the excellent surface and bulk passivation.

Active-Matrix Organic Light Emission Diode Pixel Circuit for Suppressing and Compensating for the Threshold Voltage Degradation of Hydrogenated Amorphous Silicon Thin Film Transistors

A new hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) pixel circuit for active-matrix organic light emission diodes (AM-OLEDs), which significantly compensates the OLED current degradation by memorizing the threshold voltage of driving TFT and suppresses the threshold voltage shift of a-Si:H TFTs by negative bias annealing, is proposed and fabricated. During the first half of each frame, the driving TFT of the proposed pixel circuit supplies current to the OLED, which is determined by modified data voltage in the compensation scheme. The proposed pixel circuit was able to compensate the threshold voltage shift of the driving TFT as well as the OLED. During the remaining half of each frame, the proposed pixel circuit induces the recovery of the threshold voltage degradation of a-Si:H TFTs owing to the negative bias annealing. The experimental results show that the proposed pixel circuit was able to successfully compensate for the OLED current degradation and suppress the threshold voltage degradation of the driving TFT.

Hydrogenated Amorphous Silicon Thin-Film Transistors on Freestanding Graphite Foil

We have studied the fabrication of hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) on 125 μm thick graphite foil. The a-Si:H TFT fabricated on polyimide planarized graphite foil exhibited a field-effect mobility of 0.32 cm 2 /V s, a threshold voltage of 2.35 V, and subthreshold slope of 1.23 V/decade. The performance of the TFT on graphite foil is stable until bending it down to the radius of 5 mm, corresponding to the strain of 2.4%. The TFT on curved graphite foil can be freestanding on the table.

Influence of Film Thickness on Optical Properties of Hydrogenated Amorphous Silicon Thin Films

Influence of Film Thickness on Optical Properties of Hydrogenated Amorphous Silicon Thin Films

Effects of Spectral Characteristics of Backlight Sources on Photo-Leakage Currents of Hydrogenated Amorphous Silicon Thin Film Transistor

For various light sources used as backlight systems such as a cold cathode fluorescent lamp (CCFL) or a white light-emitting diode (LED), the photo-leakage characteristics of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) were analyzed and described in terms of the relationship between the spectral characteristics of light sources and the mechanism for the generation of electron–hole pairs. From the spectral analysis of the light sources, the leakage current is thought to be related to the wavelength of the peak intensity because the absorption coefficient of the a-Si:H layer is inversely proportional to the wavelength. In the case of a higher wavelength of peak intensity, the photo-leakage characteristics showed improvements in the leakage level and in the on/off current ratio despite similar luminance.

A Physical Model with the Effects of Self-Heating and Variable Resistance in Above-Threshold Region for Hydrogenated Amorphous Silicon Thin Film Transistor

A physical model that includes the effects of self-heating and variable resistance in the above-threshold region is presented for hydrogenated amorphous silicon thin film transistors (a-Si:H TFTs). The self heating effect is due to the low thermal conductivity of the gate insulator and the glass substrate. In order to predict the temperature rise as a function of device dimensions and material parameters, a steady-state thermal model derived from a system of coupled one-dimensional (1-D) energy equations and boundary conditions is presented. Then the developed thermal model is applied to study the self-heating effect in the a-Si:H TFT. In addition, the bulk resistance is decreased due to the the mechanism of space charge limited conduction in a n+–i–n+ structure. By considering both the effects of self-heating and variable resistance, a physical model in the above-threshold region has been developed. Using this model, the non-saturating output current and kink effects can be accurately described for a typical a-Si:H TFT. The accuracy of the proposed model has been verified with the experimental data.