S.S. Tneh

Porous Silicon as an Intermediate Buffer Layer for Zinc Oxide Nanorods

Zinc thin films were deposited onto porous silicon (PSi) substrates by dc sputtering using a Zn target. These films were then annealed under flowing (6 l/min) oxygen gas environment in the furnace at 600°C for 2 h. Porous silicon is used as an intermediate layer between silicon and ZnO films and it provides a large area composed of an array of voids. The PSi samples were prepared using photoelectrochemical method on n-type silicon wafer with (111) and (100) orientation. To prepare porous structures, the samples were dipped into a mixture of HF:ethanol (1:1) for 5 min with current densities of 50 mA/cm2, and subjected to external illumination with a 500 W UV lamp. The surface morphology and the nanorod structure of the ZnO films were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). We synthesized the ZnO nanorods with diameter of 80–100 nm without any catalysts or templates. The XRD pattern confirmed that the ZnO nanorods were of polycrystalline structure. The surface-related optical properties have been investigated by photoluminescence (PL) and Raman measurements at room temperature. Micro-Raman results showed that A1(LO) of hexagonal ZnO/Si(111) and ZnO/Si(100) have been observed at 522 cm–1 and 530 cm–1, respectively. PL spectra peaks are clearly visible at 366 cm–1 and 368 cm–1 for ZnO film grown on porous Si(111) and Si(100) substrates, respectively. The PL spectral peak position in ZnO nanorods on porous silicon is blue-shifted with respect to that in unstrained ZnO (381 nm).

Study of electrical characteristics of ZnO Schottky photodiode on Si substrate

Purpose – The purpose of this paper is to demonstrate the n‐ZnO/p‐Si Schottky photodiodes.Design/methodology/approach – A Zn film was deposited on silicon substrate by dc sputtering deposition technology from high purity zinc (Zn) targets. Then, the Zn films were then annealed under flowing oxygen (O2) gas environment in the furnace. ZnO nanorods morphologies have been successfully prepared through a simple method. No catalyst is required.Findings – The structures and morphologies of the products were characterized in detail by using X‐ray diffraction, energy dispersive X‐ray, and scanning electron microscopy (SEM). According to experimental results, the current‐voltage characteristics of the device show the typical rectifying behaviour of Schottky diodes. The UV photocurrent measurement was performed using an UV lamp under a reverse bias.Originality/value – The paper demonstrates that the n‐ZnO/p‐Si diodes exhibit strong rectifying conduct described by the current‐voltage (I‐V) measurement under a dark a...

STRUCTURAL AND OPTICAL PROPERTIES OF LARGE-SCALE ZnO NANOWIRES AND NANOSHEETS PREPARED BY DRY THERMAL OXIDATION

In this work, we report the morphology and optical properties of zinc oxide (ZnO) layers prepared by dry thermal oxidation at different annealing conditions. Morphology studies using scanning electron microscope (SEM) show that the amount of nanowires and nanosheets increases with the introduction of a flow of O2 gas. High-resolution X-ray diffraction (HR-XRD) data show that typical polycrystalline ZnO nanostructure layers have been deposited. Near-perfect stoichiometry of Zn and O atom vacancies has been observed from energy dispersion spectroscopy (EDS) spectrum. Photoluminescence (PL) spectra show strong peaks at UV and green regions. An increase in the stoichiometry of ZnO has been achieved with the oxygen gas flow during annealing indicating that deep-level defects represented by interstitial oxygen and antisite oxygen are gas pressure dependent. A single exciton peak with binding energy 60 meV has been observed at room temperature.

Ohmic-rectifying conversion of Ni contacts on ZnO and the possible determination of ZnO thin film surface polarity.

The current-voltage characteristics of Ni contacts with the surfaces of ZnO thin films as well as single crystal (0001) ZnO substrate are investigated. The ZnO thin film shows a conversion from Ohmic to rectifying behavior when annealed at 800°C. Similar findings are also found on the Zn-polar surface of (0001) ZnO. The O-polar surface, however, only shows Ohmic behavior before and after annealing. The rectifying behavior observed on the Zn-polar and ZnO thin film surfaces is associated with the formation of nickel zinc oxide (Ni1-xZnxO, where x = 0.1, 0.2). The current-voltage characteristics suggest that a p-n junction is formed by Ni1-xZnxO (which is believed to be p-type) and ZnO (which is intrinsically n-type). The rectifying behavior for the ZnO thin film as a result of annealing suggests that its surface is Zn-terminated. Current-voltage measurements could possibly be used to determine the surface polarity of ZnO thin films.

Synthesis of Porous Ni-Doped SnO2 Thin Film by Using Spray Pyrolysis

Doping SnO2 with metal cations has been tested for photo-catalytic applications by shifting the threshold for photonic excitation of the tin oxide (SnO2) towards the visible. Nevertheless, as far as we know, there is no report on how Ni-doping of SnO2thin films by the spray pyrolysis method has been carried out. In this work, we report a new kind of experimental realization of a porous Ni-doped SnO2 thin film on glass, which is based on a spray pyrolysis process at room temperature. To prepare porous structures, the Ni-doped SnO2 thin film samples were annealed at 400° C for 1 h in air. As a result, this porous Ni-doped SnO2 thin film possesses a high specific surface area and unbroken porosity, which is especially desirable for gas sensor design. The surface morphology of the porous Ni-doped SnO2 films was examined using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and atomic force microscopy (AFM). The root-mean-square (rms) surface roughness value determined from AFM image is 11.85 nm on a 5 × 5 μm2 scan area.

The Effects of Thermal Treatments on Microstructure Phosphorus-Doped ZnO Layers Grown by Thermal Evaporation

The ZnO films doped with 3 wt% phosphorus (P) were produced by activating phosphorus doped ZnO (ZnO:P) thin films in oxygen (O2) ambient at 600°C for 30, 60, 90 and 120 min, respectively. As-deposited films doped with phosphorus are highly conductive and n type. All the films showed p-type conduction after annealing, in an O2 ambient atmosphere. The activation energies of the phosphorus dopant in the p-type ZnO under O2 ambient gases indicate that phosphorus substitution on the O site yielded a deep level in the gap. With a further increase of the annealed durations, the crystalline quality of the ZnO:P sample is degraded. The best p-type ZnO:P film deposited at 600°C for 30 min shows a resistivity of 1.85 Ω cm and a relatively high hole concentration of 5.1 × 1017cm–3 at room temperature. The films exhibit a polycrystalline hexagonal wurtzite structure without preferred orientation. The mean grain sizes are calculated to be about 60, 72, 78, 85 and 90 nm for the p-type ZnO films prepared at 600°C for 30, 60, 90 and 120 min, respectively. Room temperature photoluminescence (PL) spectra of the ZnO film exhibit two emission bands — paramount excitonic ultraviolet (UV) emission and weak deep level visible emission. The excellent emission from the film annealed at 600°C for 30 min is attributed to the good crystalline quality of the p-type ZnO film and the low rate of formation of intrinsic defects at such short duration. The visible emission consists of two components in the green range.

Single Crystalline ZnO Nanowires by Oxidizing Granular Zinc Film

In this work, we report an in situ synthesis method to produce ultra fine ZnO nanowires by a basic combination of thermal evaporated and thermal oxidation being used. ZnO nanowires were produced by a basic process with no catalyst, which is oxidizing granular Zn films at temperature (450–600°C). Initially, the zinc film was starting to produced by evaporated deposition in an atmosphere at ambient temperature using granulated Zn as the target. Then, annealed in an air or oxygen atmosphere, ZnO nanowires began to grow from Zn nanograins. The investigations have showed that the nanowires grow from porous Zn films and a little of oxygen gas flow was useful to the growth of nanowires. When annealed at 600°C in an oxygen atmosphere, the ZnO nanowires was obtained from annealed, which have a diameter less than 60 nm. It shows a good structural quality.

STRUCTURAL AND OPTICAL PROPERTIES OF ZnO SYNTHESIZED BY TEMPERATURE GRADIENT THERMAL OXIDATION

In this work, a series of polycrystalline ZnO samples have been synthesized from Zn thin films deposited on Si(100) substrates by using thermal oxidation technique. The ZnO thin film samples grown by this technique were then characterized by a variety of structural and optical characterization tools. The results revealed that the use of novel annealing process i.e. the application of temperature gradient in the thermal treatment could enhance the structural and optical quality of the ZnO thin films significantly as compared to the normal annealing process, i.e. a fixed temperature under different durations. Apart from the improvement of structural and optical properties of ZnO thin films, another striking feature of this novel annealing process was the promotion of the growth of ZnO nanostructures.

Synthesis, characterization, and effect of concentration variation on metal oxide nanostructures

Zinc oxide (ZnO) has been successfully synthesized by an anodization method, and it has been fabricated through anodization method with different concentration of zinc nitrate. The element composition, surface inspection, structural, and morphological features of the products are depend on the concentration of zinc nitrate. At lower concentration (0.01M), SEM image shows ZnO nanowires with average width of about 30 and 50 nm. With increase in the concentration of zinc nitrate from 0.01 to 0.05 M, the nanowires change into the nanosheets with average width of about 0.5 and 1.5 μm. For samples (0.1 M) exhibits nanodots, morphology was composed of hundreds of nanosheets with thickness is about 90 nm on average. When the concentration increases to 0.2 M, the nanodots trench became bigger with diameter about 1.2–2.0 μm. When the concentration of zinc nitrate is 0.3 M, the average diameter of nanodots is about 2–2.5 μm. The trench of nanosheets becomes thinner and shorter, but the number of nanosheets increases with diameter 20–50 nm. The formation of nanowires, nanodots, and nanosheets nanostructures is also believed to result from actions on concentration of zinc nitrate as an aquas medium. The EDX result shows the atomic percentage (at.%) of the oxygen increased when the concentration of zinc nitrate increased. The pattern of EDX indicates that the ZnO nanostructures are composed of Zn, O, and Al. They represent Al composition in the sample because the anode using the aluminum rod during experiment.

Electrical Characterization of Al/Ag Contacts on Al-Zn Codoped SnO2 Thin Films Deposited by Solid-State Chemical Vapor Deposition

Excellent tin oxide (SnO2) ohmic and Schottky contacts are need for device utilizations and essential electrical characterization. Up to now, metal contact property studies on SnO2 are inadequate and provide miscellaneous results. Ohmic contacts have been studied on high quality epitaxial n-type tin oxide thin films that were grown by solid state chemical vapor deposition (SSCVD). To the best of our knowledge, this is the first time that Al-Zn co-doped SnO2 films grown by SSCVD have been reported. Non-alloyed Al/Ag, Al, and Ag contacts were characterized by current-voltage measurements. Ohmic contacts were realized using Al, Ag , and Al/Ag after an air treatment of the SnO2 surface.