Sb-doped ZnO Nanowires Research Articles

Boosting the piezoelectric coefficients of flexible dynamic strain sensors made of chemically-deposited ZnO nanowires using compensatory Sb doping

The piezoelectric devices made of ZnO nanowires have received a great interest in the past decade as potential nanogenerators and sensors. However, their characteristics are still limited significantly by the screening of the piezoelectric potential generated under mechanical solicitations, originating from the high density of free electrons in ZnO nanowires. In order to tackle that issue, we develop the compensatory Sb doping of ZnO nanowires grown by chemical bath deposition, both in the low- and high-pH regions using Sb glycolate and ammonia as chemical additives. The adsorption process of Sb(III) species on the positively charged surfaces of ZnO nanowires proceeds through attractive electrostatic forces, resulting in the significant incorporation of Sb dopants with an atomic ratio in the range of 0.11–0.45%. The optical properties of Sb-doped ZnO nanowires exhibit additional phonon modes related to Sb dopants in the range of 500–750 cm-1 in the Raman spectra, and some specific characteristics in the nature and intensity of radiative recombination in the cathodoluminescence spectra. Importantly, the integration of Sb-doped ZnO nanowires encapsulated in PMMA and grown on PDMS into flexible piezoelectric dynamic strain sensors is shown to drastically boost the piezoelectric charge and voltage coefficients by a factor of 2.65 and 1.91, following the significant incorporation of Sb dopants. A subsequent thermal annealing under oxygen atmosphere is revealed to further increase the piezoelectric charge and voltage coefficients by an additional factor of 1.38 and 1.49, following the activation of Sb doping and engineering of hydrogen-related defects. Two figures-of-merit are eventually derived from the piezoelectric charge and voltage coefficients and their values for flexible piezoelectric composites made of annealed Sb-doped ZnO nanowires are compared to more conventional piezoelectric materials, showing their high potential for medical devices. The present findings highlight the strategy consisting in simultaneously introducing compensatory acceptors and engineering hydrogen-related defects to reduce the screening effect, representing an additional powerful way to enhance the characteristics of the piezoelectric devices integrating ZnO nanowires.

Preparation and characterization of self-assembled ZnO nanowire devices: nanowire strain sensor and homogeneous p–n junction

In this work, intrinsic and p-type ZnO nanowires (NWs) have been synthesized. Pure intrinsic ZnO nanowires have been fabricated by direct oxidation method and their aspect ratio reached up to 271.3. Sb-doped ZnO nanowires were uniformly grown on Si substrates by chemical vapor deposition with diameters ranging from 0.5 to 5 μm and lengths ranging from 100 μm to 3 mm. Directional arrangement of nanowires has been realized by two self-assembly methods, pulling method and water flow method, and two kinds of ZnO nanodevices (strain sensor and homogenous p–n junction) were prepared and characterized based on the directional arranged nanowires. According to the current response of ZnO nanowire strain sensor, the deformation quantities of elastic plate under the action of external forces in orthogonal X and Y direction were calculated respectively. The ZnO nanowire homogenous p–n junction was made of two vertical Sb-doped and intrinsic ZnO nanowires. The I–V characteristic curve showed good rectification characteristics, and the forward turn-on voltage was about 10 V. However, since the current was too small due to the small carrier concentration in the ZnO single crystal, it is difficult to achieve electroluminescence at present.

Synthesis, characterization and UV photodetector application of Sb-doped ZnO nanowires

Sb-doped ZnO nanowires with hexagonal wurtzite structures have been synthesized via chemical vapor deposition method, and the main charge state of Sb dopants is Sb5+. The photoluminescence spectra demonstrate the existence of shallow acceptors, SbZn-2VZn complexes in all probability. On the other hand, Sb doping caused more native and impurity donors in Sb-doped ZnO nanowires. Then, field effect transistors of single Sb-doped ZnO nanowire were fabricated and the transport properties shows n-type conductivity. The competition between shallow acceptors and donors, and the influence of Sb valency need to be investigated further to obtain stable Sb-doped p-type ZnO. At last, we have shown the potential application of Sb-doped ZnO nanowires for nanoscale UV photodetector.

Enhanced optoelectronic properties of thermally evaporated Sb-doped ZnO nanowires via defect structures

Sb-doped ZnO nanowires were fabricated on Si (100) substrates by thermal evaporation via the vapor-liquid-solid mechanism at 850 °C, and their optoelectronic properties were examined. Two prominent emission regions at the near band-edge emission and deep-level emission of the pure ZnO nanowires were observed in the photoluminescence spectra. Doping with Sb reduced the intensities of near band edge emission and deep-level emission. Almost no near band-edge emission signal was obtained at Sb ≥ 2.2 at. % and almost no deep-level emission signal was obtained at Sb ≥ 5.46 at. %, owing to the formation of metallic Sb and the +5 oxidation state of the Sb2O5 phases. These results suggest that the Sb dopant content is the critical factor in improving the optoelectronic properties of Sb-doped ZnO nanowires, as revealed by their photoluminescence spectra.

Investigation of nanoscale voids in Sb-doped p-type ZnO nanowires

While it has multiple advantageous optoelectronic and piezoelectric properties, the application of zinc oxide has been limited by the lack of a stable p-type dopant. Recently, it was discovered that antimony doping can lead to stable p-type doping in ZnO, but one curious side effect of the doping process is the formation of voids inside the nanowire. While previously used as a signifier of successful doping, up until now, little research has been performed on these structures themselves. In this work, the effect of annealing on the size and microstructure of the voids was investigated using TEM and XRD, finding that the voids form around a region of Zn7Sb2O12. Furthermore, using Raman spectroscopy, a new peak associated with successful doping was identified. The most surprising finding, however, was the presence of water trapped inside the nanowire, showing that this is actually a composite structure. Water was initially discovered in the nanowires using atom probe tomography, and verified using Raman spectroscopy.

Optoelectronic Properties of Solution Grown ZnO n-p or p-n Core-Shell Nanowire Arrays.

Sb doped ZnO nanowires grown using the low-temperature hydrothermal method have the longest reported p-type stability of over 18 months. Using this growth system, bulk homojunction films of core-shell ZnO nanowires were synthesized with either n or p-type cores and the oppositely doped shell. Extensive transmission electron microscopy (TEM) characterization showed that the nanowires remain single crystalline, and the previously reported signs of doping remain intact. The electronic properties of these films were measured, and ultraviolet photodetection was observed. This growth technique could serve as the basis for other optoelectronic devices based on ZnO such as light emitting diodes and photovoltaics.

An Sb-doped p-type ZnO nanowire based random laser diode

An electrically pumped Sb-doped ZnO nanowire/Ga-doped ZnO p–n homojunction random laser is demonstrated. Catalyst-free Sb-doped ZnO nanowires were grown on a Ga-doped ZnO thin film on a Si substrate by chemical vapor deposition. The morphology of the as-grown titled nanowires was observed by scanning electron microscopy. X-ray photoelectron spectroscopy results indicated the incorporation of Sb dopants. Shallow acceptor states of Sb-doped nanowires were confirmed by photoluminescence measurements. Current–voltage measurements of ZnO nanowire structures assembled from p- and n-type materials showed a typical p–n diode characteristic with a threshold voltage of about 7.5 V. Very good photoresponse was observed in the UV region operated at 0 V and different reverse biases. Random lasing behavior with a low-threshold current of around 10 mA was demonstrated at room temperature. The output power was 170 nW at 30 mA.

Laser doping of Sb into ZnO nanowires in the Sb nanoparticle-dispersed liquid

We succeed in fabricating Sb-doped ZnO nanowires by laser doping using Sb nanoparticles (Sb NPs). Vertically aligned ZnO nanowires with a diameter of 100 nm were synthesized by the nanoparticles-assisted pulsed laser deposition. Sb NPs were prepared by laser ablation in liquid. The average size of 50 nm Sb NPs was successfully fabricated by laser ablation in ethanol. Subsequently, laser doping was performed by irradiating Nd:YAG laser beam (355 nm) in Sb-dispersed ethanol. After laser doping, the tip of ZnO nanowires was slightly deformed into spherical shape by laser heating. A rectifying property with a threshold voltage of 4.5 V was observed between n-type ZnO nanowires and Sb-doped ZnO nanowires.

Opto-electrical properties of Sb-doped p-type ZnO nanowires

P-type ZnO nanowires (NWs) have attracted much attention in the past years due to the potential applications for optoelectronics and piezotronics. In this study, we have synthesized Sb-doped p-type ZnO NWs on Si (100) substrates by chemical vapor deposition with Aucatalyst. The Sb-doped ZnO NWs are single crystalline with high density, grown along [1-1-2] direction. The doping percentage of Sb is about 2.49%, which has been confirmed by X-ray photoelectron spectroscopy. The ZnO NW field effect transistor demonstrated its p-type characteristics. A high responsivity to ultraviolet photodetection was also observed. In addition, compared to intrinsic ZnO NWs, the conductivity of the Sb-doped ZnO NWs exhibited ∼2 orders of magnitude higher. These properties make the p-type ZnO NWs a promising candidate for electronic and optoelectronic devices.

Theoretical investigation of the effects of doping on the electronic structure and thermoelectric properties of ZnO nanowires

The effects of doping ZnO nanowires with Al, Ga and Sb on their electronic structure and thermoelectric properties are investigated by first-principles calculations. We find that the band gap of ZnO nanowires is narrowed after doping with Al and Ga, while band gap broadening is observed in Sb doped ZnO nanowires. The lattice thermal conductivity of ZnO nanowires is obtained based on the Debye-Callaway model. The thermoelectric properties of ZnO nanowires were calculated using the BoltzTraP code. The results show that there exists an optimal carrier concentration yielding the maximum value of ZT for Al, Ga and Sb doped ZnO nanowires at room temperature. The maximum value of ZT, 0.147, is obtained for Ga doped ZnO nanowires, when the carrier concentration is 3.62 × 10(19) cm(-3). The figure of merit ZT of Sb doped ZnO nanowires is higher than that of Ga doped ZnO nanowires when the temperature is between 400 K and 1200 K. We also find that Al doped ZnO nanowires always have poor thermoelectric properties, which means that the Al dopant may not be the optimal choice for ZnO nanowires in thermoelectric applications.

Optical evidence for donor behavior of Sb in ZnO nanowires

High-resolution photoluminescence (PL) experiments show that Sb doped ZnO nanowires exhibit shallow donor bound exciton (D0X) transitions at 3364.3 meV, which is shallower than the well-known In, Ga, Al, and H D0X transitions. The relative intensity of the Sb D0X transition scales with dopant concentration. Temperature dependent PL measurements show that the Sb D0X behaves like other D0X transitions with a thermal activation energy close to the spectroscopic binding energy. No evidence of an ionized donor bound exciton (D+X) is observed, consistent with the expectation from Haynes' rule that such a state would have a higher energy than the free exciton.

Head-to-head Inversion Domain Boundaries in Sb-doped p-type ZnO Nanowires

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Influence Of ZnO Buffer Layer On Growth Of Sb Doped ZnO Nano Wires Using Nano Particle Assisted Pulsed Laser Deposition (NAPLD) Using Sb As Catalyst

Influence of ZnO buffer layer thickness on the structural and optical properties of the Sb catalyzed/doped ZnO nanowires synthesized using NAPLD has been investigated. Buffer layer with a thickness of 100 nm, 800 nm and 1600 nm coated with Sb are used as a substrate and pure ZnO was used as a target to synthesize Sb doped ZnO nanowires. Introduction of the buffer layer lead to the growth of vertically aligned along with horizontally grown ZnO nano wires. With the increase in buffer layer thickness, the core diameter of the vertically grown ZnO nano wires was subsequently increased. Nano wires synthesized with a buffer layer thickness of 1600 nm showed a significant change in the lattice constants, resulting in measurable lower angle of about 0.06o from XRD, widening of lattice fringe spacing of 0.54 nm from TEM and Suppression of A1T and E1(L0) modes in Raman Spectroscopic. In addition a strong UV emission with absence of visible emission was observed from the room temperature PL. This confirms the generation of Sb doped ZnO nano wire with high crystal quality. Copyright © 2012 VBRI Press.

Synthesis and characterization of one-dimensional vertically aligned Sb-doped ZnO nanowires

Vertically aligned undoped ZnO and Sb-doped ZnO nanowires have been synthesized on a silicon substrate using the vapor–solid technique, without using a catalyst or predeposited buffer layers. The structure and morphology of the as-synthesized nanowires are characterized using X-ray diffraction, scanning and transmission electron microscopies, selected area electron diffraction, and electron dispersive X-ray spectroscopy. The results showed that the use of Si(111) is a critical factor for the growth of vertically aligned nanowires. This is a result of the lattice match on Si(111), which is more favorable with the ZnO lattice structure because the Si(111) surface is hexagonal and has a smaller lattice constant of 3.840 Å. The photoluminescence properties were also investigated at room temperature (300 K). The UV peaks of undoped and Sb-doped ZnO nanowires are located at 3.33 and 3.29 eV, respectively. This redshift of 0.04 eV in the Sb-doped ZnO indicates a reduction of the ZnO band gap caused by the Sb dopant. The temperature-dependent photoluminescence spectra of Sb-doped ZnO nanowires from 10 to 300 K were also examined. This measurement showed that at 10 K several peaks appear, at 3.36, 3.23 and 3.04 eV, which were assigned as acceptor-bound excitons, a donor–acceptor pair and a zinc-vacancy-related peak, respectively. These peaks are shifted with the increase of temperature up to 300 K.

Stable p-Type Conduction from Sb-Decorated Head-to-Head Basal Plane Inversion Domain Boundaries in ZnO Nanowires

We report that Sb-decorated head-to-head (H-H) basal plane inversion domain boundaries (b-IDBs) lead to stable p-type conduction in Sb-doped ZnO nanowires (NWs) due to Sb and O codoping. Aberration-corrected Z-contrast scanning transmission electron microscopy shows that all of the Sb in the NWs is incorporated into H-H b-IDBs just under the (0001) NW growth surfaces and the (0001) bottom facets of interior voids. Density functional theory calculations show that the extra basal plane of O per H-H b-IDB makes them electron acceptors. NWs containing these defects exhibited stable p-type behavior in a single NW FET over 18 months. This new mechanism for p-type conduction in ZnO offers the potential of ZnO NW based p-n homojunction devices.

Influence of Sb in synthesize of ZnO nanowire using sandwich type substrate in carbothermal evaporation method

The paper deals with synthesis of Sb doped ZnO nanowire by considering Si coated with Sb and Au as substrate using carbothermal evaporation method. The horizontally oriented Sb doped ZnO nanowires with a diameter of 1μm synthesized at 900°C, which is quite high as compared to the Pure ZnO nanowires generated without the influence of Sb at 900°C. The nanowire synthesized at 900°C showed a measurable lower angle of about 0.06° from XRD and suppression of A1T and E1(L0) modes in Raman spectroscopic, this confirms the incorporation of Sb in ZnO lattice. The strong exciton emission and weak deep-level emission from room temperature PL and Strong emission attributed to the radiant recombination from neutral–acceptor–bound exciton (A0X) peak accompanied by two strong and broad emission of donor acceptor pair (DAP) from low temperature PL, this confirms the use of Sb as an acceptor for ZnO.

Impact of forward bias injection on minority carrier transport in p-type ZnO nanowires

Minority carrier diffusion length in p-type Sb-doped ZnO nanowires was measured as a function of temperature and forward bias injection duration. The minority carrier diffusion length displays a thermally activated length increase with the energy of 144 ± 5 meV. The forward bias injection exhibits an increase in diffusion length with the activation energy of 217 ± 20 meV, indicating the possible involvement of a SbZn-2VZn acceptor complex.

An aqueous solution-based doping strategy for large-scale synthesis of Sb-doped ZnOnanowires

An aqueous solution-based doping strategy was developed for controlled doping impurityatoms into a ZnO nanowire (NW) lattice. Through this approach, antimony-doped ZnONWs were successfully synthesized in an aqueous solution containing zinc nitrate andhexamethylenetetramine with antimony acetate as the dopant source. By introducingglycolate ions into the solution, a soluble antimony precursor (antimony glycolate) wasformed and a good NW morphology with a controlled antimony doping concentration wassuccessfully achieved. A doping concentration study suggested an antimony glycolateabsorption doping mechanism. By fabricating and characterizing NW-based field effecttransistors (FETs), stable p-type conductivity was observed. A field effect mobility of1.2 cm2 V − 1 s − 1 and a carrierconcentration of 6 × 1017 cm − 3 were achieved. Electrostatic force microscopy (EFM) characterization on doped andundoped ZnO NWs further illustrated the shift of the metal–semiconductor barrier due toSb doping. This work provided an effective large-scale synthesis strategy for doping ZnONWs in aqueous solution.

Twinning-induced kinking of Sb-doped ZnO nanowires

Sb-doped ZnO nanowires with kinking structures have been synthesizedby a catalyst-free thermal evaporation method with the addition ofSb2O3. Transmission electron microscopy (TEM) observations revealed that the kinks of thenanowires are induced by twinning structures. , twins and heavy stacking faults in the (0001) plane were observed in these kinkednanowires. High-resolution TEM and energy dispersive x-ray spectroscopy showed thatthere exists an Sb-rich segregation layer in the twin boundaries of some nanowires. Aformation mechanism of the kinked nanowires was proposed. The optical property of thesynthesized nanowires was investigated by room-temperature photoluminescence.

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.