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 electron trap at ∼0.16eV below the conduction band.

No abstract

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%.

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 p-CuO/n-ZnO thin film heterojunction is fabricated on a glass substrate by the sol-gel technique. The crystallinity of the junction materials and microstructure of the top p-layer are examined by an x-ray diffractometer (XRD) and scanning electron microscope (SEM). The current-voltage (I-V) characteristics of the p-n heterojunction and its temperature dependence have been investigated in air and H 2 ambient. Although the junction possesses linear I-V characteristics from room temperature (RT) to 150 • C in air, at higher temperatures (200 • C to 300 • C), it shows nonlinear rectifying behaviour. The forward current is greatly increased with increasing temperature while the reverse current is increased slightly resulting in a I F /I R ratio as high as 485. The ideality factor (n) is 4.88 at a temperature of 300 • C. The forward current is highly increased by the introduction of H 2 gas at 300 • C. However, a simultaneous increase in the reverse current makes the I F /I R ratio 8.4. It is observed that H 2 sensitivity of the heterojunction is increased with the increase in temperature as well as the thickness of CuO film. A sensitivity value as high as 266.5 is observed at 300 • C when biased at 3 V in the presence of approximately 3000 ppm of H 2 .