Parmanand Sharma

Analysis of ultraviolet photoconductivity in ZnO films prepared by unbalanced magnetron sputtering

Photoresponse characteristics of polycrystalline ZnO films prepared by the unbalanced magnetron sputtering technique have been analyzed for ultraviolet photodetector applications. Changes in the cr ...

H2S gas sensing mechanism of SnO2 films with ultrathin CuO dotted islands

H2S gas interaction mechanisms of sputtered SnO2 and SnO2–CuO bilayer sensors with a varying distribution of the Cu catalyst on SnO2 are studied using Pt interdigital electrodes within the sensing film. Sensitivity to H2S gas is investigated in the range 20–1200 ppm. Changes induced on the surface, the SnO2–CuO interface, and the internal bulk region of the sensing SnO2 film upon exposure to H2S have been analyzed to explain the increasing sensitivity of three different sensors SnO2, SnO2–CuO, and SnO2 with CuO islands. SnO2 film covered with 0.6 mm diameter ultrathin (∼10 nm) CuO dots is found to exhibit a high sensitivity of 7.3×103 at a low operating temperature of 150 °C. A response speed of 14 s for 20 ppm of H2S, and a fast recovery time of 118 s in flowing air have been measured. The presence of ultrathin CuO dotted islands allow effective removal of adsorbed oxygen from the uncovered SnO2 surface due to spillover of hydrogen dissociated from the H2S–CuO interaction, and the spillover mechanism is ...

Ultraviolet photoresponse of porous ZnO thin films prepared by unbalanced magnetron sputtering

Fast ultraviolet photoresponse is observed in ZnO thin films prepared by unbalanced magnetron sputtering. Films with a porous microstructure and a mixed (100), (002) and (101) crystallographic orientation exhibit photoresponse with good linearity and minimal aging effects. A fast rise time of 792 ms and a fall time of 805 ms are observed under low intensity (9.5 mW/cm2, λ=365 nm) ultraviolet light.

Interaction of surface acoustic waves and ultraviolet light in ZnO films

The frequency response of a 37 MHz bulk LiNbO 3 surface acoustic wave (SAW) filter with a 200-nm-thick ZnO overlayer exhibited a downshift in the frequency with ultraviolet (UV) light due to acoustoelectric interactions between the photo-generated carriers in the semiconducting ZnO and the surface acoustic waves. In contrast, a 36 MHz ZnO thin film SAW delay-line with insulating ZnO films exhibited an upshift in the frequency. The response was more pronounced at higher harmonics (130-315 MHz) and was attributed to changes in the elastic/dielectric properties in the upper surface layer of ZnO. A linear change in the frequency with UV intensity shows immense applicability for wireless ultraviolet sensor applications.

Low-intensity ultraviolet light detector using a surface acoustic wave oscillator based on ZnO/LiNbO3 bilayer structure

A surface acoustic wave (SAW) based ultraviolet (UV) light detector configured in the form of a SAW oscillator is investigated. The SAW oscillator consists of a ZnO/LiNbO3 bilayer structure, where ZnO is used as UV light sensing material and LiNbO3 is used to excite the surface acoustic waves. The SAW oscillator is characterized for its functional performance at different Vcc, the voltage to the oscillator circuit, under different levels of UV light illumination. The changes in the amplitude and the frequency shift of the SAW oscillator output exhibit a linear variation with UV light intensity. The SAW UV detector is shown to be highly sensitive at lower Vcc. A low level UV intensity of 450 nW cm?2 is easily detectable and the voltage responsivity is estimated to be ~24 kV W?1.

Imaging of piezoelectric activity in laser-ablated c-axis-oriented LiNbO3/ZnO thin film multilayer on glass using atomic force microscopy

A LiNbO 3 /ZnO multilayer with a preferred c -axis orientation normal to the plane of the substrate was grown on glass and SiO 2 /Si substrates by laser ablation. The piezoelectric activity in as-deposited films was demonstrated using a novel approach to the atomic force microscope. In the presence of an in-plane, low-frequency (0.1–5 Hz) alternating current electric field, we monitored and imaged the induced piezoelectric response normal to the film plane between two electrodes.

Interaction of Surface Acoustic Waves with Ultraviolet Light

Fabrication and functional performance of highly sensitive ultraviolet detectors based on zinc oxide (ZnO) thin film SAW device and a ZnO/LiNbO 3 layered structure is described. A 37 MHz bulk LiNbO 3 surface acoustic wave (SAW) filter with a 71 to 200 nm-thick ZnO over layer exhibits a downshift in the frequency with ultraviolet (UV) light due to acoustoelectric interactions between the photo-generated carriers in the semiconducting ZnO over layer and the surface acoustic waves. In contrast, a 36 MHz ZnO thin film SAW delay-line fabricated on a 8 μ m thick insulating ZnO film exhibited an upshift in the frequency. A linear change in frequency shift with UV intensity is found useful for the fabrication of wireless UV sensors.

Piezoelectric Activity in c-Axis Oriented LiNbO3/ZnO Bilayers Grown by Laser Ablation Technique

LiNbO 3 /ZnO multi-layer with a preferred c-axis orientation has been grown on glass and SiO 2 /Si substrates by laser ablation technique. The piezoelectric activity in as deposited films is demonstrated using a novel approach to the atomic force microscope. In the presence of an in plane low frequency (0.1 to 5 Hz) ac electric field, we monitor and image the induced piezoelectric response normal to the film plane between two electrodes.