Search

Mg x Zn1−x O (x = 0.0–0.08) thin films have been deposited on glass substrate by sol–gel technique and photoconductivity of the thin films have been investigated in vacuum, hydrogen, oxygen and air. Photoresponse spectra show that both ZnO and substituted films are ultraviolet light sensitive and the sensitivity shifts towards the shorter wavelength side with increasing x. The photo-to-dark current ratio (I ph/I d) and decay times are influenced by different ambient such as vacuum, hydrogen, and air for all the substituted films. I ph/I d for the substituted films increases first attaining a maximum value for x = 0.05 and then decreases for vacuum and hydrogen, while, an increase in the value is observed incase of oxygen as x increases. The change is not significant in air. The value of photo to dark current ratio for the films with x = 0.05 and 0.08 is as high as four orders of magnitude in both vacuum and hydrogen ambient. This change in the photo to dark current ratio is correlated with the grain boundaries, hence, the grain size of the films. In vacuum, hydrogen and oxygen, though a large increase in the photocurrent is caused, both growth and decay process becomes slower in these ambient.

A series of n-ZnO/p-Si thin film heterojunctions have been fabricated by a low cost sol–gel technique for different ZnO film thicknesses and the dark as well as photo current–voltage (I–V) characteristics have been investigated in details. The heterojunction with ZnO thickness of 0.46 μm shows the best diode characteristics in terms of rectification ratio, IF/IR = 5.7 × 103 at 5 V and reverse leakage current density, JR = 7.6 × 10−5 A cm−2 at −5 V. From the photo I–V curves and wavelength dependent photocurrent of the heterojunctions, it is found that the junction with 0.46 μm ZnO thickness shows the highest sensitivity towards both UV and visible lights.

ZnO thin films are deposited on the glass substrates by sol–gel drain coating technique by varying the concentration of the sol. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used to investigate the effect of sol concentration on the crystallinity and surface morphology of the films. The results show that with increase in sol concentration, the value of full width at half maximum (FWHM) of (0 0 2) peak decreases while the strain first increases and then decreases. The sol with higher concentration results in the increase in the grain size. The studies on the optical properties show that the band gap value increases from 3.27 to 3.3 eV when the sol concentration changes from 0.03 to 0.1 M. The photoconductivity studies reveal that the film for 0.05 M sol shows the maximum photoresponse for ultraviolet (UV) wavelength (

A series of Al doped ZnO (ZnO : Al) films with different Al concentrations have been deposited on glass substrates using the sol–gel spin coating technique and the effect of Al concentrations on the structural, electrical, optical and photoresponse properties have been investigated. The XRD results show the presence of peaks due to the reflections of the planes from a wurtzite type of ZnO structure. The surface morphology shows that the grains become non-uniform and smaller in size as the Al doping level increases. For 1–2% Al doping, the film attains highest carrier concentration of about ~2.7 × 1019 cm−3 and lowest resistivity of ~2 × 10−2 Ω cm. The excitonic nature in the absorption spectrum disappears for doping above 1%. The band gap increases with the increase in the Al concentration. The photoconductivity studies show that although the photoresponse properties are degraded due to incorporation of Al atoms, the 1% Al doped film shows the best photoresponse properties within the doping limit up to 5%.

We report on the bias-dependent photodetection of two different wavelengths of photons in the ultraviolet (UV) region by Au-Mg0.1Zn0.9O/ZnO-Ag structure deposited on a glass substrate by the sol-gel technique. Without the cap layer of Mg0.1Zn0.9O, the current-voltage (I-V) characteristic is symmetric and linear for positive and negative bias conditions. The presence of a cap layer on top of ZnO resulted in an asymmetric I-V curve and also decreased the dark current for both bias voltages applied to the Au contact. The structure shows maximum photoresponse at 370 nm and 320 nm when the Au contact is positively and negatively biased, respectively. The photo-to-dark current density ratio is about 48 at +20 V.

The dependence of photoconducting properties on the thickness of ZnO films deposited on glass substrates by sol–gel spin coating technique has been investigated. The X-ray diffraction (XRD) results indicate that the film with thickness of 260 nm becomes maximum oriented along (0 0 2) direction. The field emission scanning electron micrograph (FESEM) shows that the grain size and volume of micropore increases with increase in thickness. Calculation shows that 260 nm film has the highest porosity. The photoconductivity studies exhibit maximum photoresponse for ultraviolet (UV) wavelength (

The effect of Cu doping (0.08-4%) on the structural, electrical, optical, and optoelectronic properties of sol-gel ZnO thin films deposited on glass substrates have been investigated. X-ray diffraction studies show that the doped films are single-phase wurtzite structure with random orientations. A decreasing trend in the c-axis parameter up to 0.5% is observed followed by an increasing trend above that. Field-emission scanning electron microscopy shows a grain texture. The energy dispersive spectroscopy as well as the film color confirms the Cu doping. Optical transmittance measurements show 80% transparency in the visible region for the films up to 0.3% Cu content. The doped films become very resistive as indicated by the four probe electrical resistivity and current-voltage measurements. The photoluminescence spectra reveal with Cu doping, a green emission at 515 nm appeared and the UV peak intensity at 376 nm is drastically lowered. However, no green emission is observed as the doping is increased beyond 0.5%. The changes in the structural, electrical, and optical properties are correlated to interstitials defects. The photoconductivity studies show that the UV sensitivity of the films is enhanced up to 0.1%, which indicates that the films can be used as UV sensors.

A simple route for the synthesis of a novel mesoporous zinc oxide material having wurtzite like nanocrystalline pore walls by using Schiff-base amine as template is reported, which shows very high BET surface area (456 m(2) g(-1)) and remarkably enhanced photoconductivity and photoluminescence at room temperature under visible light irradiation vis-à-vis bulk ZnO material.

Single layer ZnO/polyaniline (PANI) inorganic/organic hybrid structure fabricated on glass substrate by depositing polyaniline film on the sol-gel ZnO thin film shows a rectifying behavior indicating the formation of a diode. The current transport mechanism is modeled through an energy band diagram. The heterojunction is sensitive to UV illumination. The photo-to-dark current ratio of the junction is about 46 for −5V bias. The photoresponse parameters of the diode are found to be better than those of only ZnO film of similar thickness. The results indicate that the ZnO/PANI hybrid structure might be promising for the UV photodetection applications.

A n‐ZnO∕p‐Si thin film heterojunction has been fabricated by a low cost sol-gel technique. The wavelength dependent photoresponse properties of the heterojunction is investigated in detail by studying the effect of light illumination on current-voltage (I‐V) characteristics, photocurrent, and photocapacitance spectra at room temperature. It shows good diode characteristics with IF∕IR=3.4×103 at 4V and reverse leakage current density of 7.6×10−5Acm−2 at −5V. From the photocurrent spectra, it is observed that the visible photons are absorbed in the depleted p‐Si under reverse bias conditions, while ultraviolet (UV) photons are absorbed in the depleted n‐ZnO under positive bias conditions. This indicates that such a sol-gel n‐ZnO∕p‐Si thin film heterojunction can be used to sense both UV and visible photons though the photoresponse for UV is much slower than that of visible. The photocapacitance measurements suggest the presence of a shallow defect level in the sol-gel derived ZnO film which acts as an elect...