Hexagon platinum Schottky contact with ZnO thin film for hydrogen sensing

This paper reports on the study of the effect on adding total peripheries and sharp edges to the Schottky contact as a hydrogen sensor. Schottky contact was successfully designed and fabricated as hexagon-shape. The contact was integrated together with zinc oxide thin film and tested towards 1% hydrogen gas. Simulations of the design were conducted using COMSOL Multiphysics to observe the electric field characteristic at the contact layer. The simulation results show higher electric field induced at sharp edges with 4.18×104 V/m. Current-voltage characteristic shows 0.27 V voltage shift at 40 μA biased current.

Low threshold voltage ZnO thin film transistor with a Zn0.7Mg0.3O gate dielectric for transparent electronics

A highly transparent all ZnO thin film transistor (ZnO-TFT) with a transmittance of above 80% in the visible part of the spectrum, was fabricated by direct current magnetron sputtering, with a bottom gate configuration. The ZnO-TFT with undoped ZnO channel layers deposited on 300 nm Zn0.7Mg0.3O gate dielectric layers attains an on/off ratio of 104 and mobility of 20 cm2/V s. The capacitance-voltage (C−V) characteristics of the ZnO-TFT exhibited a transition from depletion to accumulation with a small hysteresis indicating the presence of oxide traps. The trap density was also computed from the Levinson’s plot. The use of Zn0.7Mg0.3O as a dielectric layer adds additional dimension to its applications. The room temperature processing of the device depicts the possibility of the use of flexible substrates such as polymer substrates. The results provide the realization of transparent electronics for next-generation optoelectronics.

Role of substrate temperature on the properties of Na-doped ZnO thin film nanorods and performance of ammonia gas sensors using nebulizer spray pyrolysis technique

Sodium doped zinc oxide (Na:ZnO) thin films were deposited on glass substrates at substrate temperatures 300,400 and 500 degrees C by a novel nebulizer spray method. X-ray diffraction shows that all the films are polycrystalline in nature having hexagonal structure with high preferential orientation along (0 0 2) plane. High resolution SEM studies reveal the formation of Na-doped ZnO films having uniformly distributed nano-rods over the entire surface of the substrates at 400 degrees C. The complex impedance of the ZnO nano-rods shows two distinguished semicircles and the diameter of the arcs got decreased in diameter as the temperature increases from 170 to 270 degrees C and thereafter slightly increased. (c) 2013 Elsevier B.V. All rights reserved.

Cu2O substrates and epitaxial Cu2O/ZnO thin film hetero-structures for solar energy conversion

Future fossil fuel scarcity and environmental degradation have demonstrated the need for renewable, low-carbon sources of energy to power an increasingly industrialized world. Solar energy with its infinite supply makes it an extraordinary resource that should not go unused. However with current materials, adoption is limited by cost and so a paradigm shift must occur to get everyone on the same page embracing solar technology. Cuprous Oxide (Cu2O) is a promising earth abundant material that can be a great alternative to traditional thin-film photovoltaic materials like CIGS, CdTe, etc. We have prepared Cu2O bulk substrates by the thermal oxidation of copper foils as well Cu2O thin films deposited via plasma-assisted Molecular Beam Epitaxy. From preliminary Hall measurements it was determined that Cu2O would need to be doped extrinsically. This was further confirmed by simulations of ZnO/Cu2O heterojunctions. A cyclic interdependence between, defect concentration, minority carrier lifetime, film thickness, and carrier concentration manifests itself a primary reason for why efficiencies greater than 4% has yet to be realized. Our growth methodology for our thin-film heterostructures allow precise control of the number of defects that incorporate into our film during both equilibrium and nonequilibrium growth. We also report process flow/device design/fabrication techniques in order to create a device. A typical device without any optimizations exhibited open-circuit voltages Voc, values in excess 500mV; nearly 18% greater than previous solid state devices.

Growth and properties of ZnO thin film on beta-Ga2O3(100) substrate by pulsed laser deposition

Zinc oxide (ZnO) thin films were grown on the beta-Ga2O3 (100) substrate by pulsed laser deposition (PLD). X-ray diffraction (XRD) indicated that the ZnO films are c-axis oriented. The optical and electrical properties of the films were investigated. The room temperature Photoluminescence (PL) spectrum showed a near band emission at 3.28 eV with two deep level emissions. Optical absorption indicated a visible exciton absorption at room temperature. The as-grown films had good electrical properties with the resistivities as low as 0.02 Omega cm at room temperature. Thus, beta-Ga2O3 (100) substrate is shown to be a suitable substrate for fabricating ZnO film. (c) 2006 Elsevier B.V. All rights reserved.

Optical properties of ZnO thin film on gamma-LiAlO2 substrate grown by pulsed laser deposition

Optical properties were investigated of ZnO thin films grown oil (100) gamma-LiAlO2 (LAO) substrates by pulsed laser deposition method. C-axis oriented ZnO film was grown oil (100) LAO substrate at the substrate temperature of 550 degrees C. The transmittances of the films were over 85%. Peaks attributed to excitons were seen in the absorption spectra, indicating that the thin films have high crystallinity. Photoluminescence spectra were observed at room temperature; the peak at 550 urn is ascribed to oxygen vacancies in the ZnO films caused by the diffusion of Li from the substrate into the film during deposition. (c) 2005 Elsevier B.V. All rights reserved.

Characterization of m-plane ZnO thin film on gamma-LiAlO2 (100) substrate by metal-organic chemical vapor deposition

Non-polar (1 (1) over bar 00)m-plane ZnO thin film has been prepared on gamma-LiAlO2 (100)substrate via the low pressure metal organic chemical vapor deposition. Obvious intensity variation of the E-2 mode in the polarized Raman spectra and the absorption edge shift in the polarized optical transmission spectra indicate that the m-plane film exhibits optical anisotropy, which have applications in certain optical devices, such as the UV modulator and polarization-dependent beam switch. From the atomic force microscopy images, highly-oriented uniform-sized grains of rectangular shape were observed. (c) 2008 Elsevier B.V. All rights reserved.

ZnO thin film surface acoustic wave based lab-on-a-chip

Lab-on-a-chip (LOC) is one of the most important microsystem applications with promise for use in microanalysis, drug development, diagnosis of illness and diseases etc. LOC typically consists of two main components: microfluidics and sensors. Integration of microfluidics and sensors on a single chip can greatly enhance the efficiency of biochemical reactions and the sensitivity of detection, increase the reaction/detection speed, and reduce the potential cross-contamination, fabrication time and cost etc. However, the mechanisms generally used for microfluidics and sensors are different, making the integration of the two main components complicated and increases the cost of the systems. A lab-on-a-chip system based on a single surface acoustic wave (SAW) actuation mechanism is proposed. SAW devices were fabricated on nanocrystalline ZnO thin films deposited on Si substrates using sputtering. Coupling of acoustic waves into a liquid induces acoustic streaming and motion of droplets. A streaming velocity up to ∼ 5cm/s and droplet pumping speeds of ∼lcm/s were obtained. It was also found that a higher order mode wave, the Sezawa wave is more effective in streaming and transportation of microdroplets. The ZnO SAW sensor has been used for prostate antigen/antibody biorecognition systems, demonstrated the feasibility of using a single actuation mechanism for lab-on-a-chip applications. © 2010 Materials Research Society.

Protein functionalized ZnO thin film bulk acoustic resonator as an odorant biosensor

ZnO thin film bulk acoustic resonators (FBARs) with resonant frequency of ∼1.5 GHz have been fabricated to function as an odorant biosensor. Physical adsorption of an odorant binding protein (AaegOBP22 from Aedes aegypti) resulted in frequency down shift. N,N-diethyl-meta-toluamide (DEET) has been selected as a ligand to the odorant binding protein (OBP). Alternate exposure of the bare FBARs to nitrogen flow with and without DEET vapor did not cause any noticeable frequency change. However, frequency drop was detected when exposing the OBP loaded FBAR sensors to the nitrogen flow containing DEET vapor against nitrogen flow alone (control) and the extent of frequency shift was proportional to the amount of the protein immobilized on the FBAR surface, indicating a linear response to DEET binding. These findings demonstrate the potential of binding protein functionalized FBARs as odorant biosensors. © 2012 Elsevier B.V. All rights reserved.

ZnO thin film photoconductive ultraviolet detector with fast photoresponse

C-axis preferred oriented ZnO thin films were prepared on quartz substrates by RF sputtering. Photoconductive ultraviolet detector with planar interdigital electrodes was fabricated on ZnO thin film by the lift off technique. Linear I-V characteristic was observed under dark or 365 nm UV light illumination and has obvious difference. The photoresponsivity of 365 nm at 5 V bias is 18 A/W. The response time measure set mainly contains KrF excimer laser with the pulse width of 30 ns and the oscillograph with the bandwidth of 200 MHz. The result shows fast photoresponse with a rise time of 100 ns and fall time of 1.5 mu s. (c) 2005 Elsevier B.V. All rights reserved.