Increasing Illumination Level Research Articles

Investigation of electrical and photovoltaic properties of Au/n-Si Schottky diode with BOD-Z-EN interlayer

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) based BOD-Z-EN compound was used as an interfacial organic layer to fabrication of Au/BOD-Z-EN/n-Si/In diode. The electrical parameters of Au/BOD-Z-EN/n-Si/In diode such as ideality factor (n), barrier height (Φb) and series resistance (Rs) have been investigated through current–voltage (I–V) studies at dark and under various illumination intensities to understand the effect of interlayer on the device properties. The values found for the n varied from 2.33 to 1.55 and the Φb ranged from 0.86 to 0.90 eV as the illumination condition changed from dark to 100 mW/cm2. Series resistance (Rs) values calculated using Cheung’s method were found to decrease with increasing illumination level. The forward bias I–V characteristics of the diode were explained by the space charge limited current theory. The main photovoltaic parameters such as open circuit voltage (Voc), short circuit current density (Jsc) and fill factor (FF) were determined for various light intensity. The Au/BOD-Z-EN/n-Si/In diode exhibits a photovoltaic behavior with a Voc of 150 mV and Jsc of 10 µA/cm2 under 100 mw/cm2. In addition, photosensitivity and photoresponsivity properties of the diode were determined. All these results indicate that Au/BOD-Z-EN/n-Si/In device can be used as photosensor in optoelectronic applications.

The response of high barrier Schottky diodes to light illumination

We have investigated the illumination effect on electrical characteristics of nearly ideal Yb/p-Si Schottky diodes with a high zero-bias barrier height (Φbo). The value of reverse bias current increased as the illumination level increased for these diodes. The electrical parameters such as ideality factor (n) and Φbo were obtained as 1.09 and 0.80 eV in dark, respectively. n increases with increasing illumination level whereas Φbo decreases. The series resistance calculated using Cheung functions almost did not change with the illumination level. The characteristics of capacitance–voltage and conductance-voltage were obtained as a function of illumination level, applied bias voltage and frequency. The effect of illumination on the capacitance–voltage and conductance-voltage characteristics was clearly observed for 10 kHz frequency whereas the illumination did not affect the characteristics for 1 MHz frequency, significantly. The photovoltaic parameters such as open circuit voltage of 0.21 V, short circuit current of 1.60 × 10–5 A, and fill factor of 62% were obtained for 1040 W/m2. These values have changed with increasing illumination level. The effect of illumination on the density of the interfacial states was observed. The experimental findings have showed that the diodes are sensitive to illumination and have photovoltaic behavior. The Yb/p-Si Schottky diodes are promising for photodiode applications.

Synthesis, electrical and photo-sensing characteristics of the Al/(PCBM/NiO: ZnO)/p-Si nanocomposite structures

In this study, metal-oxide (NiO:ZnO) nanocomposites mixed with different weight-percentages (2, 10, 20 % NiO) content were coated on the p-Si wafer via spin-coating method. The optical and electrical features of the Al/(PCBM/NiO:ZnO)/p-Si structures/diodes were investigated and compared via current-voltage/time (I–V/t) and capacitance/conductance-voltage-frequency (C/G–V-f) characteristics in dark and various illumination intensities (20, 40, 60, 80, 100 mW/cm2) at room temperature. Main electrical parameters of them such as ideality factor (n), barrier height (Φb), rectification ratio (RR = IF/IR) and series resistance (Rs) were calculated for each percentage (2, 10, and 20 % NiO). Experimental results show that the best percentages of NiO is 20 % in respect of high value of RR and low Rs, but the value of n increases with increasing in percentages. The transient photocurrent increases with increasing illumination level. The slope (m) of the double-logarithmic Iph-P plots were found as 0.67, 0.87 and 0.82, respectively, and these slopes confirmed that these nanocomposites exhibit photoconduction behaviour and hence Al/(PCBM/NiO:ZnO)/p-Si structure can be used a photo device/sensor. The observed changes in the I with illumination, C and G with frequency are the results of interface states (Nss) located at (PCBM/NiO:ZnO)/p-Si interface and so reorder and restructure of them under illumination, bias voltage, and frequency.

Photodiode based on Al-doped SnO2: Fabrication, current-voltage and capacitance-conductance-voltage measurements

Al doped tin oxide (Al:SnO2)11Diodes. are fabricated onto silicon substrate by easy spray pyrolysis route. The room temperature current-voltage (I–V) measurements of Ag/Al:SnO2/n-Si/Au junction are taken under dark and various illumination level. The reverse and forward current increase with the increasing of illumination intensity, gradually. The device exhibits good photodiode properties but a photovoltaic behavior is not observed. Ideality factor values is found to be 7.54 and 5.41 two distinct linear region of the I–V curve of the junction under dark. Its value varies between 4.87 and 5.80 under light. The zero-bias barrier height decreases with increasing illumination level. The value of series resistance obtained from generalized Norde plot have showed a strong dependence on illumination level. Its value is calculated as 1.83 kΩ and 0.91 kΩ under dark and illumination level of 190 mW/cm2, respectively. The space limited current (SCLC) conduction mechanism is investigated under dark and light conditions. The frequency dependence of capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of the junction are analyzed in a wide range of applied voltage (from -8 V to + 8 V). The thickness of Al:SnO2 thin film is obtained as 360 nm by using C and G data at 1 MHz and 8 V.

Electrical characterizations of Au/ZnO/n-GaAs Schottky diodes under distinct illumination intensities

The Au/ZnO/n-GaAs Schottky barrier diode was fabricated and examined regarding to its current–voltage characteristics under distinct illumination intensities at room temperature. The reverse biased current increases with increasing illumination level while forward biased current is almost unchanged with illumination which states that the fabricated diodes exhibit photosensitive character or photodiode behavior. Hence, the shunt resistance is decreased with illumination while the series resistance is almost remained constant. The increment in the ideality factor after illumination can be ascribed to the assumption of inhomogeneities at M/S interface. Considering the ideality factor and the voltage dependent effective barrier height, the energy distribution profiles of surface states (Nss) were formed by the forward bias current–voltage data and increased with increasing illumination level. The Nss values acquired by considering series resistance are lower than those acquired by ignoring series resistance. Consequently, surface states can serve as recombination centers and have great importance especially in reverse bias current–voltage characteristics.

Illumination effect on I‐V, C‐V and G/w‐V characteristics of AlTiWPd2Si/nSi structures at room temperature

AbstractIn this study, the forward and reverse bias current‐voltage (I‐V), capacitance‐voltage (C‐V) and conductance‐voltage (G/w‐V) characteristics of AlTiWPd2Si/nSi structures were measured at room temperature. In order to see the illumination effect on main structure parameters such as zero‐bias‐barrier height (ΦBo), ideality factor (n), series resistance (Rs) of structure and interface states (Nss), the forward and reverse bias I‐V, C‐V and G/w‐V characteristics of AlTiWPd2Si/nSi structures were investigated in the dark and under various levels of illumination. These main electrical parameters were obtained as function of illumination levels from these measurements. Experimental results show that both the C and G values increase with increasing illumination level due to the illumination‐induced interface states. Also, the value of Rs decreases with increasing illumination level. The Nss profile was obtained for both forward bias I‐V characteristics by taking into account the bias dependent of the ideality factor and effective barrier height (Φe) and low‐high frequency method. Copyright © 2010 John Wiley & Sons, Ltd.

Influence of space charges on the impulse response of InGaAs metal-semiconductor-metal photodetectors

The impulse response of interdigitated metal-semiconductor-metal photodetectors fabricated on an Fe-doped InGaAs absorbing layer and an Fe-doped InP barrier enhancement layer is investigated. For ultra-short pulse excitation of 150 fs at lambda =620 nm the photoresponse is found to be less than 13 ps FWHM for detectors with 1 mu m finger spacing. Above a certain level of illumination, the peak amplitude increases sublinearly and the relative contribution of the tail to the detector response is appreciably enhanced. The screening of the electric field by photo-generated space charges is responsible for this nonlinearity. For detectors with 5 mu m finger spacing illuminated with 1.3 mu m light pulses (FWHM=33 ps), space charge perturbation of the impulse response manifests itself by a decrease of the FWHM and an increase of the fall time with increasing illumination level. The practical consequences for the performance of MSM detectors in various applications are discussed. >

Diel variation in density, length composition, and feeding activity of juvenile alewife, Alosa pseudoharengus Wilson, and blueback herring, A. aestivalis Mitchill, at near‐surface depths in a hydroelectric dam impoundment

Catches ofjuvenile blueback herring in near‐surface (0 to 1.5 m depth) waters, although greater at night than during the day, did not exhibit a strict negative phototropism because catches increased significantly with increasing illumination level during the forenoon and decreased with decreasing illumination during the afternoon. Juvenile alewife were absent from near‐surface waters during daylight. Feeding activity by blueback herring increased between dawn and dusk and ceased or slowed overnight but was not strictly positively phototropic. Low power (1‐β) of statistical tests due to high sampling variability and low (in hindsight) sample sizes precluded conclusions about the absence of die1 and spatial differences in the pattern of density, length composition, and of feeding activity of juvenile Alosa in those cases where the null hypothesis could not be rejected. Acceptable statistical power would require substantially increased (perhaps impractically so) sample sizes aided by an increase in a (probability of a type I error) from 0.05 to 0.1.

The effects of factors on human performance in the event of an unexpected robot motion

This study evaluates factors that could effect human performance in the event of an unexpected robot motion. The results of the study demonstrated many things. First, robot speed and task had an important impact on robot overrun distance. A longer overrun distance was observed with both increasing robot speed or task complexity. Second, illumination affected subject's performance; a longer overrun distance was observed with a low illumination level (10 Lux). Overrun distance, however, remained unaffected with increasing illumination level above 100 Lux. Furthermore, unexpected robot motions initiated in the peripheral field resulted in a longer overrun distance than motions initiated in the central field. The analysis of the robot speed by illumination interaction suggested that a low illumination level may further increase overrun distance with increasing robot speed. The analysis also suggested that when increasing robot motion speed, the overrun distance increases with low background-to-robot-arm luminance contrast ratios.

Theory of grain boundary recombination and carrier transport in polycrystalline silicon under optical illumination

The physics controlling the recombination of minority carriers at grain boundaries in polycrystalline silicon under optical illumination is described theoretically, and a model for the grain boundary space-charge potential barrier height is presented. The model is based on the assumption of a Gaussian energy distribution of grain boundary interface states. Attention is also focused on the electrical conduction in this material under illumination. The dependence of space-charge potential barrier height and the effective recombination velocity on the illumination level, the grain size, and the bulk diffusion length of minority carriers (L/sub b/) is investigated. Computations show that if the illumination level is high, the sensitivity of effective recombination velocity to grain size (d) in the intermediate grain size range (i.e. d approximately=L/sub b/) is much higher than that in the small and large grain size ranges. It is found that the resistivity of polysilicon decreases on increasing illumination level. The dependence of polysilicon resistivity on grain size under optical illumination is found to be much higher than that under dark conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Photoelectrochemical and electrocatalytic behaviour of p-type ruthenium disulphide electrodes

Crystals of p-type RuS 2 ( E G = 1.3 eV), which showed remarkably stable photocurrents for hydrogen evolution, were grown. Despite medium quality of the semiconductor material, revealed by only moderate blocking character of the barrier, relatively high photovoltages (0.45 V) in the presence of different redox systems, and appreciable quantum efficiencies at lower light intensities, were observed. The quantum efficiency was found to decrease with increasing illumination level of the electrode due to greater influence of the recombination processes. Photoelectrochemical measurements performed in the presence of different redox species revealed the occurrence of a systematic shift in the band edge positions (Fermi level pinning) due to the presence of a high concentration of surface states. Since n-RuS 2 is a good photoelectrode for oxygen evolution, oxygen reduction was studied on p-type, as well as on degenerate, electrodes. The kinetics of such a reaction were, however, found to be slow both in acidic and basic solutions.

Current Oscillations and High-Field Domains in Photoexcited High-Resistivity GaAs

Current oscillations (10 kHz∼102 kHz) due to the periodic generation of a moving high-field domain have been observed in high-resistivity GaAs (∼3×103 ohm-cm in the dark) under illumination at room temperature. It has been found that threshold field for the oscillation decreases with increasing illumination level and lies in the range from 650 V/cm to 2100 V/cm. Properties of the high-field domain have been investigated by a light probe and a contact probe technique. The domain velocity is 103 cm/sec∼104 cm/sec. Width and field of the domain are of the order of 10-2 cm and 104 V/cm, respectively. By shifting a light spot position along the specimen to change the distance that the domain transits, the oscillation frequency can be varied continuously. The origin of the oscillations can be explained with field-enhanced electron trapping at deep levels.