Undoped nanocrystalline silicon (nc-Si:H) films were prepared by conventional 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) at 260 °C, using highly H 2 -diluted SiH 4 plasma. The nc-Si:H films were evaluated using electrical, structural, and chemical measurements. The optimized nc-Si:H film showed an oxygen concentration (Co) of ~1.5 × 10 17 at./cm 3 and a dark conductivity (σ D ) of ~10 −6 S/cm, while the Raman crystalline volume fraction (Xc) was ~85 %. Top-gate staggered TFTs with a ~100 nm nc-Si:H channel layer and an amorphous silicon oxide (a-SiO x ) as the gate dielectric were fabricated. The TFTs showed a field effect mobility (µ fe ) of ~150 cm 2 /Vs, a threshold voltage (V t ) of -2 V, a subthreshold slope (S) of ~0.25 V/dec, and an ON/OFF current ratio more than 10 6 . To the best of our knowledge, the TFT mobility reported here is the highest achieved to date using state-of-the-art nc-Si:H films prepared by direct PECVD.

The effects of post-deposition annealing and material stability of undoped and n+nanocrystalline silicon (nc-Si:H) films deposited at 75 °C using standard 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) have been investigated. Electrical, structural, and chemical composition properties of the films at ambient atmosphere were studied before and after the thermal annealing. The dark conductivity (σd) in all films demonstrated high stability against prolonged ambient atmosphere exposure, which can be attributed to stable hydrogen passivation of the grain boundaries. On the other hand, in undoped nc-Si:H films, the σdincreases by more than one order of magnitude after annealing in ambient atmosphere, followed by a decrease below the as-grown value. Depending on the annealing temperature, the σd can drop as low as 10−8 S/cm. In n+ nc-Si:H films, the decrease in the σd was lower. However, in undoped nc-Si:H films capped by an amorphous silicon nitride (a-SiN:H), this was not observed. In all films, no significant change in the film microstructure before and after annealing was detected. However, a small decrease in the hydrogen content (CH) accompanied by an increase in the oxygen content (Co) was observed in uncapped undoped nc-Si:H films. It was therefore concluded that the σd is affected by oxygen desorption due to annealing and its absorption from the ambient atmosphere. Based on experimental results, we propose a possible model in terms of hydrogen effusion-assisted oxygen absorption.

We report on the fabrication and characterization of penetration-type semi-transparent hydrogenated amorphous silicon (a-Si:H) pin solar cells on flexible plastic substrates. Device-grade solar cell layers were designed and fabricated at a maximum process temperature of 150 degrees C, which is suitable for plastic substrate application. The solar cell layers were characterized using electrical, structural, and optical measurements, while optical and electrical measurements were carried out for the solar cells along with mechanical durability test. The flexible semi-transparent a-Si:H solar cells showed an average visible range (500-800 nm) optical transmittance of 34.2% and a power conversion efficiency (PCE) of similar to 5.0%. The fabricated solar cells also showed good flexibility and durability from rigid bending cycling test. The device performance demonstrated the effectiveness of semi-transparent a-Si:H solar cells enabling low-cost, light-weight functional energy-harvesting applications.

We report on a ZnO-based LC-type passive humidity sensor (HS) using a scalable, large-area thin-film semiconductor fabrication process. The reported sensor is capable of monitoring relative humidity (RH) remotely. The fabricated sensor is 30 mm in diameter and comprises an LC resonator formed via an octagonal planar inductor and a moisture sensitive interdigitated ZnO capacitor in series. A printed circuit board reader coil, which can sense the sensor output from <25 mm distance, is also reported. The HS is demonstrated to read 30%–90% of RH by interrogating the change in resonance frequency ( ${f}_{R}$ ) of the reader-senor system. The reading resolution was ±2.38% RH and the sensor sensitivity ranged from 53.33 kHz to 93.33 kHz for a 1% change in RH during measurements above 45% RH. Experimental results also showed that the fabricated sensor is operational for a range of 0 °C−75 °C as long as calibration is performed for temperature drifts of ≥±3 °C. The reported results are promising to expedite the deployment of novel inexpensive sensor, for example, in sealed locations to remotely monitor humidity without a need for on-sensor power.

We report for the first time the application of a hydrogenated, amorphous-Si solar-cell as a self-powered (i. e., no external power) detector for visible-light that we briefly characterized using a 3D-printed microplasma.

This paper reports on a monolithic 10 cm × 10 cm area PV module integrating an array of 72 a-Si:H n-i-p cells on a 100 μm thick polyethylene-naphtalate substrate. The n-i-p stack is deposited using a PECVD system at 150 o C substrate temperature. The design optimization and device performance analysis are performed using a two-dimensional distributed circuit model of the photovoltaic cell. The circuit simulator SPICE is used to calculate current and potential distributions in a network of sub-cell circuits, and also to map Joule losses in the front TCO electrode and the metal grid. Experimental results show that the shunt leakage is one of the factors reducing the device performance. Current-voltage characteristics of individual a-Si:H p-i-n cells were analyzed to estimate a variation of shunt resistances. Using the LBIC technique, the presence of multiple shunts in the n-i-p cell was detected. To understand the nature of electrical shunts, the change in the surface roughness of all device layers was analyzed throughout fabrication process. It is found that surface defects in plastic foils, which are thermally induced during the device fabrication, form microscopic pinholes filled with highly conductive top electrode material.

This letter reports on microcrystalline silicon near infrared (NIR) photodiode detector. The fabricated device shows dynamic ratio of 200 at 850 nm wavelength per 0.2 mW/cm2 of incident power density at reverse bias voltage of $-1\,\,V$ with response time of $400~\mu s$ . The dynamic ratio achieved here is 15 times higher than the state of art large area inorganic a-SiGe:H phototransistor and twice the one for state of art organic cyanine based NIR detector. The speed of this device is 40 times faster than the a-SiGe:H detector. The overall advantage of high dynamic ratio and fast response alongside with compatibility with standard a-Si:H thin film transistor industry makes this device suitable for large area NIR detection applications.

Anodic nanoporous alumina (NPA) is known to be a low cost material suitable for fabrication of templates for the growth of a variety of nanostructured materials, membranes and sensors. In this work, nanoporous alumina was prepared in 0.4 M oxalic acid by a two-step anodization process. The properties of nanoporous alumina film grown on aluminum foil were studied by atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy. The microscopy investigations confirm the pore formation in the produced layers and the process of anodization allows consistent fabrication of nanoporous alumina. The effect of anodization process parameters on the size of the nanopores and the distance between them were studied and good agreement with published data was found. Hence a desired diameter of the pores and the distance between of it can be obtained by adjusting the electrolyte and oxidation voltage.

This paper reports on device-quality silicon-carbon alloy (a-SiC:H) application as an absorber material in semi-transparent solar cells. Films with an optical bandgap ranging from 2 to 2.3 eV were prepared by plasma enhanced chemical vapour deposition (PECVD). The n-i-p structures with undoped SiC:H layers deposited under the same experimental conditions were also fabricated and characterized. The optimized devices showed forward current-voltage characteristics with a diode ideality factor in the range from 1.4 to 1.8, and an open circuit voltage up to 0.92 V. The density of deep defect states in a SiC:H was estimated from the transient current measurements and correlated with the optical bandgap.

This article reports on characterization of hydrogenated amorphous silicon (a-Si:H) photovoltaic modules fabricated on 100μm thick PEN plastic films. Experimental results show that the shunt leakage is one of the factors reducing the device performance. Current-voltage characteristics of individual a-Si:H p-i-n cells were analysed to estimate a variation of shunt resistances. A SPICE model of the a-Si:H p-i-n cell with local shunt leakage was also developed to analyse the impact of leakage currents on the device performance. Using the LBIC technique, the presence of multiple shunts in the cell was detected. They are attributed to surface defects in plastic foils, which are thermally induced during the device fabrication.

This paper studies the effect of deposition temperature on the growth of nanocrystalline silicon (nc-Si) films deposited by 13.56MHz plasma enhanced chemical vapor deposition (PECVD) with in-situ hydrogen (H) passivation. A high crystalline volume fraction (XC) of 80% was found in the ~100nm nc-Si film deposited at 260°C with 99% H2 diluted SiH4 at intermediate RF power between the power-limited and precursor-limited regimes. Based on these optimized deposition conditions, 300–400nm nc-Si films deposited at 75–260°C also showed a high XC of 82–85%, an intrinsic-like dark-conductivity (σdark) of ~10−6S/cm, and even a low mean oxygen content (CO) of 1017–1018at./cm3. Although material properties were similar, deposition temperature appeared to change the qualitative structure of the nanocrystalline grains. The preferred grain orientation changed from 〈111〉 to 〈220〉 as the deposition temperature was increased from 75 to 260°C due to enhanced surface diffusion of deposition precursors. This reflected in more compact and lateral columnar growth of nc-Si films with increasing deposition temperature. We successfully demonstrated high field-effect hole and electron mobilities of 33.8 and 225cm2/Vs, respectively, in top-gate thin-film transistors (TFTs) employing the ~100nm nc-Si channel layer deposited at 260°C.

Solar cells on lightweight and flexible substrates have advantages over glass- or wafer-based photovoltaic devices in both terrestrial and space applications. Here, we report on development of amorphous silicon thin film photovoltaic modules fabricated at maximum deposition temperature of 150 °C on 100 μm thick polyethylene-naphtalate plastic films. Each module of 10 cm × 10 cm area consists of 72 a-Si:H n-i-p rectangular structures with transparent conducting oxide top electrodes with Al fingers and metal back electrodes deposited through the shadow masks. Individual structures are connected in series forming eight rows with connection ports provided for external blocking diodes. The design optimization and device performance analysis are performed using a developed SPICE model.

This article reports on amorphous silicon solar cells on plastic foils in the substrate configuration having a front metal grid. A two-dimensional distributed circuit model of the photovoltaic cell has been developed for performance analysis and device design optimization. The circuit simulator SPICE is used to calculate current and potential distributions in a network of sub-cell circuits. This approach enables a realistic device model that predicts output current-voltage characteristics and maps Joule losses in the TCO electrode and the metal grid. As an example of usage, the optimization of contact grid geometry at various TCO sheet resistances has been performed.

In this letter, we study the response time characteristics of lateral hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon metal-semiconductor-metal (MSM) photodetectors. Devices with response time of 71 mu s under green light illumination with lambda = 525 nm (the wavelength of choice for indirect X-ray imaging) have been fabricated. The results show 42-fold and 4.2-fold improvement over the state of art single layer a-Si: H and double layer a-Si:H/molybdenum-disulphide (MoS2) MSM detectors, respectively.

Optical feedback driving schemes can enable accurate ageing and pixel brightness non-uniformity corrections in AMOLED displays. Here, we report on a pixel driver utilizing a metal-insulator-semiconductor (MIS) sensor for luminance control of the OLED element. In the proposed pixel architecture for bottom-emission AMOLEDs, the embedded MIS sensor shares the same layer stack with back-channel etched a-Si:H TFTs to maintain the fabrication simplicity. Performance characteristics of the MIS sensor are presented and analyzed to demonstrate its feasibility. Details on the pixel circuit functionality including the sensing and programming operations are also discussed.

This work reports a carbon-free, blue-enhanced a -Si:H n-i-p photodiode with an optimized protocrystalline p -layer. Although the used deposition conditions for the p -layer correspond to the microcrystalline regime, thin layers are mostly protocrystalline due to the amorphous underlying undoped layer. This conclusion is supported by Raman spectroscopy measurements. We have also found that the optical band gap of the p -layer can be varied by adjusting the rf power. By widening the band gap and tuning the impurity concentration in the p -layer, absorption and recombination losses at the p-i interface were reduced. The current-voltage, capacitance-voltage, and spectral-response characteristics of fabricated photodiodes are correlated with the doping level, optical band gap, and deposition conditions for p -layers. The optimized device exhibits a leakage current of about ∼80 pA/cm 2 at 5 V reverse bias. The external quantum efficiency reaches a peak value of 92% at a wavelength of 510 nm, and, at shorter wavelengths, decreases down to 66%@400nm.

This letter reports on fabrication of a low-cost high-dynamic range near infrared (NIR) photodiode detector on glass substrate using thin films of hydrogenated nanocrystalline silicon (nc-Si:H) prepared by 13.56-MHz plasma-enhanced chemical vapor deposition. The fabricated device shows more than two orders of magnitude enhancement in external quantum efficiency compared with the conventional hydrogenated amorphous silicon (a-Si:H) photodiode in the wavelength region of 830-950 nm. The short circuit dark current density of the nc-Si:H device is 22.3 nA/cm 2 , which is only four times higher than that of a-Si:H photodiode. As a result, the dynamic range of operation for nc-Si:H device is at least 35 times higher than its amorphous counterpart in the wavelength region of interest, making it suitable for digital NIR imaging applications.

This paper presents a new driving scheme utilizing an in-pixel metal-insulator-semiconductor (MIS) photosensor for luminance control of active-matrix organic light-emitting diode (AMOLED) pixel. The proposed 3-TFT circuit is controlled by an external driver performing the signal readout, processing, and programming operations according to a luminance adjusting algorithm. To maintain the fabrication simplicity, the embedded MIS photosensor shares the same layer stack with pixel TFTs. Performance characteristics of the MIS structure with a nc-Si:H/a-Si:H bilayer absorber were measured and analyzed to prove the concept. The observed transient dark current is associated with charge trapping at the insulator-semiconductor interface that can be largely eliminated by adjusting the bias voltage during the refresh cycle. Other factors limiting the dynamic range and external quantum efficiency are also determined and verified using a small-signal model of the device. Experimental results demonstrate the feasibility of the MIS photosensor for the discussed driving scheme.