Sb-doped ZnO Research Articles

Electrochemical determination of l-Cysteine by an elbow shaped, Sb-doped ZnO nanowire-modified electrode

Elbow shaped Sb-doped ZnO nanowires (SZO NWs) have been synthesized via thermal evaporation and thoroughly characterized. A glassy carbon (GC) electrode was modified by these NWs for the determination of L-cystein (L-CySH). Detailed electrochemical measurements of the modified electrode towards L- CySH oxidation are investigated. The response current of L-CySH oxidation at the SZO/GC electrode is found to be much higher than that of the bare GC and ZnO/GC electrodes. This change in the electrochemical properties of the modified electrode is due to the reduction in band gap and an increased amount of deep-level defects in SZO NWs, which leads to a significant role in the L-CySH determination. The modified electrode exhibits a reproducible sensitivity of 400 nA μM−1, within a response time of less than 6s, a detection limit of 0.025 μM and a linear range of 0.075 to 100 μM. Furthermore, the modified electrode shows high stability and good resistance to interference. Our investigation demonstrates that SZO NWs are very sensitive to L-CySH and can be employed in the development of biosensors for future biological and medical applications.

Fabrication of ZnO and ZnO:Sb Nanoparticles for Gas Sensor Applications

ZnO and Sb‐doped ZnO nanoparticles were successfully prepared using sol‐gel technique. Different concentrations of triethanolamine (TEA) were utilized as the preparation procedure to act as complexing agent that enhances the doping probability of the formed Sb‐doped ZnO nanopowder. Thick films of the prepared nanopowders were fabricated with spinner coating. Morphological characteristics, phase structure, chemical composition, thermal stability, and optical properties of the prepared nanopowders were measured and analyzed. The average crystallite size of ZnO and ZnO:Sb powders ranged between 19–28 nm according to the XRD calculations and TEM observations. The gas sensitivity of the homemade devices based on Sb‐doped ZnO nanoparticles towards O2 and CO2 gases as a function of temperature was measured and compared with undoped ZnO films. The gas sensitivity of the films was greatly improved after doping with Sb and reached its maximum value of ~86% for O2 gas at 93:7 wt% of Zn:Sb.

Effect of Different Substrate Temperature on Sb-Doped ZnO Thin Films Prepared by Pulsed Laser Deposition on Sapphire Substrates

Sb-doped ZnO thin films are deposited on c-plane sapphire substrates by pulsed laser deposition. Hall results indicate that the conductivity of the Sb-doped ZnO thin films is strongly dependent on the substrate temperature. The sample deposited at the temperature of 550°C exhibits p-type conductivity. It gives a resistivity of 15.25 Ω · cm, with a Hall mobility of 1.79cm2V−1s−1 and a carrier concentration of 2.290 × 1017 cm−3 at room temperature. The x-ray diffraction indicates that the Sb-doped ZnO thin films deposited in the range of 450–650°C are high c-axis oriented. Low-temperature photoluminescence spectra indicate that the sample deposited at 550°C shows the strong acceptor-bound exciton (A0X) emission.

Mechanical and longitudinal electromechanical properties of Sb-doped ZnO nanobelts

Sb-doped ZnO nanobelts are synthesized by using a simple chemical vapor deposition method. Investigations into the mechanical and longitudinal electromechanical properties of single ZnO belts indicate that the Sb doping in ZnO can reduce the Young's modulus and enhance electromechanical response sensitivity.

Formation of stable and reproducible low resistivity and high carrier concentration p-type ZnO doped at high pressure with Sb

Stable p-type Sb-doped ZnO (ZnO:Sb) was fabricated reproducibly by sintering mixture of ZnO and Sb2O3 powders under 5 GPa at temperatures of 1100–1450 °C. The best p-type ZnO:Sb with resistivity of 1.6×10−2 Ω cm, carrier concentration of 3.3×1020 cm−3, and mobility of 12.1 cm/V s was obtained by doping 4.6 at. % Sb and sintering at 1450 °C. The p-type conduction is due to complex acceptor formed by one substitutional Sb at Zn site and two Zn vacancies. The acceptor level was measured to be 113 meV. Effect of pressure on formation and electrical properties of the p-type ZnO:Sb is discussed.

Optical properties of antimony-doped p-type ZnO films fabricated by pulsed laser deposition

We investigated optical properties of Sb-doped p-type ZnO films grown on n-Si (100) substrates by oxygen plasma-assisted pulsed laser deposition. Two acceptor states, with the acceptor levels of 161 and 336 meV, are identified by well-resolved photoluminescence spectra. Under oxygen-rich conditions, the deep acceptor in Sb-doped ZnO film is Zn vacancy. The shallow acceptor is SbZn-2VZn complex induced by Sb doping. The origin of p-type behavior in Sb-doped ZnO has been ascribed to the formation of SbZn-2VZn complex.

Non-catalytic growth of high-aspect-ratio Sb-doped ZnO nanowires by simple thermal evaporation process: Structural and optical properties

Well-crystallized high-aspect-ratio antimony (Sb)-doped ZnO nanowires have been successfully synthesized on Si(1 0 0) substrates in a large-quantity via simple thermal evaporation process by using metallic zinc and Sb powders in the presence of oxygen. It is observed from the detailed structural characterizations that the grown nanowires are well-crystallized with the wurtzite hexagonal phase and preferentially grown along the [0 0 0 1] direction. It was clearly seen from the high-resolution TEM images that the Sb-atoms are successfully doped into the lattices of ZnO nanowires. The room-temperature photoluminescence (PL) spectrum exhibited a broad band in the visible region with a suppressed UV emission, indicating the presence of structural defects due to insertion of Sb-atoms in the lattices of as-grown nanowires. Due to the enhancement of green emission in the formed nanowires, these structures show great interest for typical applications of ZnO-based phosphors, such as field emissive display technology, etc.

Synthesis and Characterization of Sb-Doped ZnO Nanobelts with Single-Side Zigzag Boundaries

Sb-doped ZnO nanobelts with single-side zigzag boundaries were synthesized by chemical vapor deposition with an Au catalyst. Transmission electron microscopy shows the existence of two types of periodic planar defects in each nanobelt, which are located on the (0001) and (0221) planes, respectively. The growth of the nanobelts is suggested to be controlled by both the two planar defects. Raman scattering analysis shows that the Sb doping in ZnO depresses the Raman A1T mode of ZnO and induces the appearance of the additional peak at 761 cm−1. The near band edge emission peak in photoluminescence spectra has red-shifted as well as broadened seriously due to the heavy doping of Sb.

First-Principles Calculation of Electronic Structure and Optical Properties of Sb-Doped ZnO

The geometric structure, electronic structure, optical properties and the formation energy of Sb-doped ZnO with the wurtzite structure are investigated using the first-principles ultra-soft pseudo-potential approach of plane wave based upon the density functional theory. The calculated results indicate that the volume of ZnO doped with Sb becomes larger, and the doping system yields the lowest formation energy of Sb on the interstitial site and the oxygen site. Furthermore, Sb dopant first occupies the octahedral oxygen sites of the wurtzite structure. It is found that Sb substituting on oxygen site behaves as a deep acceptor and shows the p-type degenerate semiconductor character. After doping, the electron density difference demonstrates the considerable electron charge density redistribution, which induces the effect of Sb-doped ZnO to increase the charge overlap between atoms. The density of states move towards lower energy and the optical band gap is broadened. Our calculated results are in agreement with other experimental results and could make more precise monitoring and controlling possible during the growth of ZnO p-type materials.

Dominant ultraviolet light emissions in packed ZnO columnar homojunction diodes

The growth of Sb-doped p-type ZnO∕Ga-doped n-type ZnO homojunction on Si (100) substrate by molecular beam epitaxy led to closely packed vertical ZnO columns with lateral diameters ranging from 100to400nm. Mesa structures were defined and Ohmic contact of both n-type ZnO and p-type ZnO was realized with Au∕Ti and Au∕NiO, respectively. I-V and C-V curves present typical electrical properties of a diode, indicating that reliable p-type ZnO was formed. Electroluminescence shows dominant ultraviolet emissions with insignificant deep-level related yellow/green band emissions at different drive currents from 60to100mA at room temperature.

Preparation of Sb-doped ZnO nanostructures and studies on some of their properties

Sb-doped ZnO nanostructures have been deposited onto glass substrates by a sol–gel method. The structural, optical and electrical properties of the Sb-doped ZnO films were characterized by various techniques including scanning electron microscopy, X-ray diffraction, UV–vis absorption, photoluminescence , and electrical transport measurements. The surface morphology of the nanostructure films is found to depend on the concentration of Sb in the source materials. Band-edge emission at 376 nm and a broad defect band around 530 nm were shown in the photoluminescence spectra. An emission band at 400 nm was also observed, which is likely associated with the interstitial Zn in ZnO. The current–voltage characteristics of the films indicate a non-linear behavior. The conductivity type of the films changes from n-type to p-type with increasing Sb-dopant.

Structural and electrical properties of Sb-doped p-type ZnO thin films fabricated by RF magnetron sputtering

We investigated the Sb-doping effects on ZnO thin film using RF (radio frequency) magnetron sputtering and RTA (rapid thermal annealing). The structural and electrical properties of the thin films were measured by X-ray diffraction, SEM (scanning electron microscope), and Hall effect measurement. Thin films were deposited at a high temperature of 800°C in order to improve the crystal quality and were annealed for a short time of only 3 min. The structural properties of undoped and Sb-doped films were considerably improved by increasing oxygen content in the Ar-O2 gas mixture. Sb-doping also significantly decreased the electron concentration, making the films p-type. However, the crystallinity and surface roughness of the films degraded and the mobility decreased while increasing Sb-doping content, likely as a result of the formation of smaller grain size. From this study, we observed the transition to the p-type behavior at 1.5 at.% of Sb. The thin film deposited with this doping level showed a hole concentration of 4.412 × 1017 cm−3 and thus is considered applicable to p-type ZnO thin film.

Controllable fabrication and electromechanical characterization of single crystalline Sb-doped ZnO nanobelts

We report the fabrication of the high-quality Sb-doped ZnO nanobelts by using a simple chemical vapor deposition method. The nanobelts consist of single-crystalline wurtzite ZnO crystal and grow along [011¯2] direction. An electromechanical system is constructed to explore the transverse electrical properties of a single nanobelt under the different applied loading forces. The I-V results indicate that a little barrier exists in between the nanobelt and the atomic force microscopy tip. An almost linear relationship between the force and the resistance was found at small deformation regions, which demonstrates that the nanobelts have potential applications as force/pressure sensor for measuring the nano-Newton forces.

Sb-doped p-ZnO∕Ga-doped n-ZnO homojunction ultraviolet light emitting diodes

ZnO p-n homojunction light emitting diodes were fabricated based on p-type Sb-doped ZnO∕n-type Ga-doped ZnO thin films. Low resistivity Au∕NiO and Au∕Ti contacts were formed on top of p-type and n-type ZnO layers, respectively. Au∕NiO contacts on p-type ZnO exhibited a low specific resistivity of 7.4×10−4Ωcm2. The light emitting diodes yielded strong near-band-edge emissions in temperature-dependent and injection current-dependent electroluminescence measurements.

Ultraviolet emission from Sb-doped p-type ZnO based heterojunction light-emitting diodes

Heterojunction light emitting diodes (LEDs) were fabricated by making Au∕Ni top Ohmic contacts on Sb-doped p-type ZnO film with low specific contact resistivity and Al∕Ti back Ohmic contacts on n-type Si substrate. Near-band edge and deep-level emissions were observed from the LED devices at both low temperatures and room temperature, which is due to band-to-band and band-to-deep level radiative recombinations in ZnO, respectively. The electroluminescence emissions precisely match those of photoluminescence spectra from Sb-doped p-type ZnO, indicating that the ZnO layer acts as the active region for the radiative recombinations of electrons and holes in the diode operation.

Electron beam induced current profiling of ZnO p-n homojunctions

Variable temperature electron beam induced current technique was employed for the profiling of ZnO p-n homojunctions and the extraction of minority electron diffusion length values in the Sb-doped p-type ZnO region. A thermally induced increase for diffusion length of minority electrons was determined to have an activation energy of ∼145meV. The latter parameter likely represents carrier delocalization energy and determines the increase of the diffusion length due to the reduction in recombination efficiency.

P-Type Sb-Doped ZnO Thin Films Prepared by Metallorganic Chemical Vapor Deposition Using Metallorganic Dopant

Reproducible p-type Sb-doped ZnO thin films were fabricated on c-plane sapphire substrates by the metallorganic chemical vapor deposition (MOCVD) technique using trimethylantimony as the doping precursor. Sb was introduced into ZnO thin films as a p-type dopant without any phase separation. Obvious donor-acceptor pair emissions were observed from photoluminescence spectra of ZnO:Sb films at 10 K. The acceptor binding energy is estimated to be ∼ 124 meV. Using the metallorganic source as the dopant of p-type ZnO thin films by the MOCVD technique is beneficial for the industrialized production of ZnO light-emitting diodes.

Al/Ti contacts to Sb-doped p-type ZnO

Sb-doped p-type ZnO film was grown on Si (100) substrate by molecular-beam epitaxy. Al/Ti metal was evaporated on the ZnO film to form contacts. As-deposited contacts were Schottky with a barrier height of 0.8 eV. Ohmic conduction was achieved after thermal annealing. The different combinations of Ohmic and Schottky contacts on Sb-doped ZnO layer led to metal-semiconductor-metal (MSM), Schottky, and photoconductive devices. Ohmic contacts on Sb-doped p-type ZnO and backside of n-type Si substrate formed a heterojunction diode. MSM, Schottky, and photoconductor devices exhibited typical electrical characteristics, however, inverted rectification was observed for heterojunction diodes. All devices exhibited ultraviolet (UV) photoresponse. Secondary ion mass spectroscopy measurements were performed on the Ohmic and Schottky contacts on Sb-doped ZnO film to trace the metal profiles before and after annealing. Mechanisms of the formation of Schottky and Ohmic contacts to Sb-doped p-type ZnO and their device operation principles are discussed. This work suggests that Al/Ti can be used as both Ohmic and Schottky contacts to Sb-doped p-type ZnO for UV detection applications.

Low-resistivity Au∕Ni Ohmic contacts to Sb-doped p-type ZnO

Au ∕ Ni contacts were fabricated on Sb-doped p-type ZnO film, which was grown on n-type Si (100) substrate with a thin undoped ZnO buffer layer by molecular beam epitaxy. As-deposited contacts were rectifying while Ohmic behavior was achieved after thermally annealing the contacts in nitrogen environment. Contact resistance was determined by linear transmission line method and it decreased with the increase of annealing temperature. Low specific contact resistivity of 3.0×10−4Ωcm2 was obtained for sample annealed at 800°C for 60s. Secondary ion mass spectroscopy was used to analyze elemental profiles of the contacts before and after annealing. Zn vacancies created by outdiffusion of Zn are believed to couple with activated Sb atoms to increase the surface hole concentration enabling Ohmic contact formation.

Response to “Comment on ‘Photoluminescence study of Sb-doped p-type ZnO films by molecular-beam epitaxy’” [Appl. Phys. Lett. 90, 116102 (2007)

Response to “Comment on ‘Photoluminescence study of Sb-doped p-type ZnO films by molecular-beam epitaxy’” [Appl. Phys. Lett. 90, 116102 (2007)