Papers by Keyword: Photoresponse

Abstract: ZnO Nanorods (NRs) is an excellent material for optoelectronic applications. However, ZnO NRs have a wide bandgap. To overcome this problem, ZnO Nanorods has been doped with nickel (0, 3, and 7 at.%) and then coated by a Cu₂O layer. The ZnO nanorods were first prepared using a hydrothermal method where nickel of varying concentration was added as a dopant. The prepared samples were then coated by Cu₂O using a Chemical Bath Deposition (CBD) method. The fabricated composites were characterized by XRD to identify the phase compositions, SEM-EDX to determine the morphology and elemental compositions, UV-Vis spectroscopy to determine the bandgap, and photocurrent response test to study the sample's response to light. The XRD reveals that the pristine ZnO and Ni-doped ZnO have the same diffraction patterns but the peaks shift to the right with increasing dopant concentrations. The SEM images of all samples show ZnO NRs grew perpendicular to the substrate while its EDX spectra confirm the presence of Nickel in the Ni-doped samples. The UV-Vis spectra showed that the calculated bandgap decreases from ~ 3.2 to 2.7 eV by increasing nickel dopant concentration and adding Cu₂O layer. The photocurrent response measurement shows that the ITO/Zn_0.93Ni_0.07O/Cu₂O sample had a good response to light compared to the two other samples.

Abstract: We report on the results of a study of the lateral photovoltaic effect in theFe3O4/SiO2/n-Si structure grown on Si(001) and Si(111) substrates. It was found that in theFe3O4/SiO2/Si(001) structure the LPE sensitivity is a half times as much, and the photoresponseparameters are about 3 times less than those in the Fe3O4/SiO2/Si(111) structure. It is supposed thata higher sensitivity and faster photoresponse in the Fe3O4/SiO2/Si(001) structure, compared with theFe3O4/SiO2/Si(111) structure, are caused by a lower density of surface states at the SiO2/Si(001)interface than at the SiO2/Si(111) interface.

Abstract: We report on the results of a study of the lateral photovoltaic effect in the Fe₃O₄/SiO₂/n-Si(001) structure at temperatures of 300 and 122 K under continuous and pulsed illumination. It is found that when the temperature changes from 300 to 122 K, the LPE sensitivity decreases from 112 to 65 mV/mm. At pulsed illumination, an increase of rise time and a fall time is observed with decreasing temperature. From a consideration of the energy band diagrams and equivalent circuits of the Fe₃O₄/SiO₂/n-Si structure, it is assumed that the detected temperature effects of LPE are due to the strong dependence of the magnetite film resistance on temperature.

Abstract: Photoresistors based on amorphous Si-Sn thin films (270-285 nm) with different concentration of tin were studied by spectral measurements of photoconductivity at room temperature and by low-temperature measurements of the Hall effect . Electrical contacts to the Si-Sn film was formed by aluminum layer deposition. When the Al contact is illuminated, the spectral sensitivity of the photoresistor with Sn consentration of 19% extends to 2060 nm due to Schottky barrier influence. It was proved that the Si-Sn alloy film provides photoresponse with cut-off energy of 0.98 eV that is close to the indirect band gap in the Si-Sn film. Three deep acceptor levels with activation energies of 90, 114, and 173 meV were found in the Si-Sn thin film (20% Sn) in the temperature range of 50 – 300 K. Sequential activation of the deep levels and their competition leads to a nonmonotonic change of the Si-Sn film conductivity (0.025 - 5.0 (Ω×cm)^-1) and mobility of holes (100 – 500 cm²/(V·s)). The transition to the intrinsic conductivity region of the amorphous Si-Sn film was not observed up to room temperature.

Abstract: Ultraviolet photodetectors (PDs) based on low-dimensional (LD) gallium oxide nanofibers were synthesized and assembled by a low cost and scalable electrospinning method. Highly uniaxially aligned nanofibers were used to assemble photodetectors. Photoconductive investigations indicate that the prepared photodetectors (PDs) are highly sensitive to ultraviolet (UV) light. The prepared photodetectors have shown a high photosensitivity (10³), fast photoresponse, excellent stability, and reproducibility under the illumination of UV light 254 nm. These electrospun nanofibers have also shown a high transparency (<85%) in the visible light 400-700 nm range. The high transparency of these nanobelts demonstrates their use for invisible UV photosensors.

Abstract: Polymer-oxide semiconductor exhibits a promising application on electronic devices. In this study, zinc oxide-polyaniline (ZnO-PAni) junctions were constructed which showed a photodiode-like behavior. The junctions were built through connecting the electrodeposited zinc oxide to electrodeposited HCl-doped polyaniline. Without illumination, the junctions exemplify a diode-like behavior (e.g., large amount current at forward-bias while small amount of current at reverse-bias). When illuminated, the junctions exhibit a photodiode-like behavior. In such, the reverse-bias current increases with light intensity.

Abstract: Multilayered thin films of aluminum-doped ZnO (Al:ZnO) have been deposited by the sol-gel dip coating technique. Experimental results indicated that the thermal annealing temperature affected the crystallinity of the Al:ZnO films. X-ray diffraction (XRD) analysis showed that thin films were preferentially orientated along the c-axis plane. The preferred orientation along (0 0 2) plane becomes more pronounced as the thermal annealing being increased. The film thickness ranges between 180 and 690 nm. In our experiments, the most optimum condition of Al:ZnO annealing temperature was both 500 oC.

Abstract: Photoresponse characteristic from efficient exciton dissociated heterojunction based on copper phthalocyanine (CuPc) and fullerene (C60) layers was observed the different spectrum responses under positive and negative biases. The nanostructures of CuPc and C60 thin films were fabricated between transparent indium tin oxide (ITO) and aluminum (Al) electrodes. The 100 nm thick of CuPc and C60 layers were deposited on patterned ITO glass substrates by thermal evaporation with quartz thickness monitor. Photoresponses of the fabricated devices were investigated by current measuring as a function of wavelength in range of 400 to 700 nm. Measured current in Al/C60/CuPc/ITO structure when applied negative voltage to ITO electrode is higher than that of positive voltage case. Under monochromatic light, the photoresponse characteristic of Al/C60/CuPc/ITO structure under negative bias shows dominate response current peak at around 450 nm and double peaks in range of 500-700 nm originated from C60 and CuPc layers, respectively. These two response characteristics can be described by the combination of responses from Al/C60/ITO and Al/CuPc/ITO structures. The response current characteristics of Al/C60/ITO and Al/CuPc/ITO structures also agree with the optical absorptions of C60 and CuPc layers, respectively. By applying positive bias to Al/C60/CuPc/ITO structure, the photoresponse characteristic has only one peak at about 450 nm that is similar to the response in Al/C60/ITO structure only. This indicates that under positive bias, the photocurrent only from C60 layer can be observed.

Abstract: Pure and Aluminium-doped ZnO (Zn_1-xAl_xO) x = 0 to 5 wt% thin films were deposited onto glass substrate by sol-gel spin coating method. The influence of various aluminium concentration in ZnO thin films on the structural, surface, optical and photoconducting properties were investigated. The GIXRD studies confirmed the polycrystalline nature with wurtzite structure of pure and Al doped ZnO films. Films with 1.5 % concentration of aluminium showed maximum absorption and transmission in the UV and visible regions respectively. The FESEM images showed crack free films with increasing grain boundaries upon doping. The average grain size is found to decrease due to aluminium doping. AFM images showed doped films with 1.5 % have better smoothness than other films. The photoconductivity measurements reveal that there is increase in the photocurrent compared to dark current for the Al doped ZnO. The photocurrent reaches its maximum value for ZnO: Al-1.5 % and then decreases upon increase in Al concentration. The photoresponse has slightly degraded upon aluminium doping onto ZnO. Temperature dependent conductivity shows that the thermal activation energy for the film decreases up to 1.5 % aluminium concentration and then increases for other concentrations in the temperature range 308 to 375K.

Abstract: Nitrogen doped amorphous carbon (n-C:N) solar cells were successfully prepared using a simple and low cost Chemical Vapor Deposition (CVD) method using camphor oil as a precursor. Four samples of n-C:N were deposited by varying the deposition temperature (500oC, 550oC, 600oC, 650oC). The fabricated solar cell using n-C:N with the configuration of Au/n-C:N/p-Si/Au achieved an increasing efficiency as temperature increase (0.000202% to 0.001089%). As a reference, pure a-C was deposited at 500oC and exhibit 0.000048% efficiency. The current-voltage (I-V) graph emphasized on the linear graph (ohmic) for the a-C thin films, whereas for the p-n device structure, a rectifying curve was obtained. Electrical conductitivity possesses increasing value (1.69 x 10-2 to 22 Ω-1 cm-1) due to increasing sp2 ratio in a-C as temperature increase. The rectifying curves signify the heterojunction between the n-doped a-C film and the p-Si substrate and designate the generation of electron-hole pair of the samples under illumination. Photoresponse characteristics of the deposited a-C was highlighted when being illuminated (AM 1.5 illumination: 100 mW/cm2, 25oC) and optical band gap for the nitrogen doped a-C is reported from 0.75 eV to 0.25 eV as temperature increase.