Sb-doped ZnO Films Research Articles

Uniform Sb doping of ZnO films with controllable morphology and enhanced optical property

In order to provide an effective and reliable approach to solving the difficulties in p-type modification of ZnO nanomaterials, in this work, we successfully synthesized ZnO films with uniform antimony distribution through low temperature aqueous growth method. The growth quality and dopant distribution of Sb-doped ZnO (SZO) films were evaluated by high-resolution micro-structural characterizations, and the growth mechanism for SZO films with various doping concentrations was discussed and revealed. Uniform and dispersive Sb distribution within SZO films contributed to the light transmittance of SZO films. The blue-shifted UV emission accompanied with weak visible light emission of SZO films were observed in room-temperature photoluminescent (PL) spectra, the rare yellow-red light emission and XPS results confirmed the existence of SbZn-related complex defects. This type of SZO films is competitive and promising for serving as the highly photo-conductive and photo-sensitive ZnO-based nanomaterials. And SZO films could be served as the basis for realizing the purpose of p-type modification with high efficiency and excellent stability.

Enhancing transparent thermoelectric properties of Sb-doped ZnO thin films via controlled deposition temperature

ZnO is known as a wide-bandgap transparent thermoelectric material. Herein, the electronic transport and temperature-dependent thermoelectric properties of transparent Sb-doped ZnO (SZO) films are reported. The sputtered SZO films prepared at the optimum deposition temperature of 673 K show an n-type semiconducting behavior with the highest thermoelectric power factor of 406 μW/mK2 at 773 K, and a good transmittance ∼82% in the wavelength region of 400–1100 nm. It can well meet the requirements for transparent thermoelectric thin films. Through X-ray diffraction, UV–Vis, and photoluminescence analyses, the Zn2+ substitution by Sb5+ can be elucidated for significantly enhancing the Seebeck coefficient and thermoelectric power factor due to the increase of density-of-state effective mass.

The origin of additional modes in Raman spectra of ZnO:Sb films

Systematic Raman spectroscopic study was conducted on the wurtzite (002) Sb-doped ZnO films grown by pulsed laser deposition with different Sb doping levels and annealed at different temperatures, with the undoped, Cu-doped and Ga-doped ZnO films for comparison. Three additional Raman modes 235 cm−1, 510 cm−1 and 534 cm−1 were observed only in the Sb-doped ZnO samples but not in the other controls. The vibration mode 235 cm−1was associated with the SbZn-related shallow donor, which was the origin of the n+-conductivity. The 510 cm−1 vibrational mode has been associated with HO in previous literature. However in the current study, the correlation between its intensity and the H abundance was not observed. The 534 cm−1 Raman mode was associated with a Sb-related defect. The variation of the intensities of the Raman modes 235 cm−1 and 510 cm−1 upon annealing and change of Sb composition were discussed.

Binding energy of Sb-related complex in p-doped ZnO film

ZnO and Sb-doped ZnO films were grown on (001) sapphire using metal organic chemical vapor deposition (MOCVD). Diethylzinc (DEZn), trimethylantimony (TMSb) and oxygen were used as the Zn, Sb and oxygen sources, respectively. The reaction mechanism of DEZn and oxygen was investigated. The formation of the SbZn–2VZn acceptor complex is explained, and the effect of the Sb chemical state on the conduction type is discussed. In the low-temperature spectrum of the Sb-doped ZnO film, emissions associated with acceptors, such as the acceptor-bound exciton (3.319 eV) and the transition between free electrons and acceptors (3.244 eV), were observed, which proved the creation of the SbZn–2VZn acceptor complex. According to the energy level of the transition between the free electrons and acceptors, the acceptor binding energy was calculated to be 0.19 eV. Meanwhile, by fitting the integral photoluminescence intensity versus the temperature function, the acceptor binding energy was also estimated and was similar to the calculated value.

ZnO:Sb MBE layers with different Sb content-optical, electronic and structural analysis

Understanding how Sb atoms are located in the ZnO crystal lattice and how they affect the layer parameters is essential to obtain p-type conductivity in ZnO:Sb. In this paper, the results of our extensive research (XPS, Raman, X-Ray, SIMS) of Sb doped ZnO films grown by Molecular Beam Epitaxy are presented. It is shown with use of high resolution X-ray Photoemission Spectroscopy (XPS) that three charge states of the Sb impurity: Sb3+, Sb5+, and Sb3− can exist in ZnO:Sb layers. The dominant charge state of Sb ions is 3 + while the contribution of 5 + is very low. The relative fraction of Sb atoms located at the Zn sites is about ∼90%, while ∼10% are incorporated in oxygen sites. It was found that increasing the Sb content in the layers increases the intensity of Raman modes at 511 cm−1, 533 cm−1, and 575 cm−1, which confirms their correlation with Sb doping. Additionally, a blue shift of the E2High Raman mode of ZnO was observed, related to the increase of strain in the oxygen sublattice. The relation between strain and stress for different Sb chemical states (Sb3+, Sb5+, Sb3−) in ZnO is calculated and compared with experimental results.

A facile and reproducible synthesis of non-polar ZnO homojunction with enlarged rectification rate and colorful light emission

A novel fabrication of non-polar Sb-doped ZnO homojunction was realized via a facile and reproducible low-temperature aqueous solution deposition in the presence of Sb dopant dissolved in ethylene glycol (EG). The undoped non-polar ZnO films were introduced as the non-polar substrates for the non-polar growth of Sb-doped ZnO film as well as the SZO/ZnO homojunction. The parameters including the reaction time and dopant concentration for the synthesis of non-polar SZO/ZnO homojunction were identified. The existence and distribution of Sb dopant in SZO layer were confirmed by X-ray photoelectron spectroscopy (XPS) and elemental mapping analysis. The I–V measurement result indicated the p-type conduction of SZO layer and the synthesized p-SZO/n-ZnO homojunction with non-polar preferred orientations possessed both ultra-low turn-on voltage (1.5 V) and large rectification rate (>105). The excitation of orange-red light emissions from deep-level energy band gap demonstrated the (SbZn-xVZn) complex defect pattern. This novel non-polar SZO/ZnO homojunction could be an excellent candidate for the applications of one-dimensional ZnO nanomaterials in the electronic/photoelectronic field.

Comprehensive study on Sb-doped zinc oxide films deposited on c-plane Al2O3 substrates

Undoped and Sb-doped p-type ZnO films were grown on (001) sapphire using metal organic chemical vapor deposition (MOCVD) technology. The crystal, optical, and electrical properties of the undoped and Sb-doped ZnO film were investigated by X-ray diffraction (XRD), photoluminescence, optical transmittance spectroscopy and Hall measurement system. The XRD patterns indicated both films exhibited preferred orientation along c axis and had a compressive stress. Strong near-band gap emissions of both films were observed in the room temperature photoluminescence spectra. Low temperature photoluminescence spectrum of the ZnO film was dominated by a donor-bound exciton with peak at 3.365 eV. To the Sb-doped ZnO film, donor-bound exciton was buried into the free exciton with peak at 3.371 eV, and emission intensities associated acceptor enhanced. The acceptor binding energy was calculated to be 0.19 eV. The optical bandgap of the Sb-doped ZnO film was estimated to be 3.302 eV. The Sb-doped ZnO film exhibited p-type conductivity with the resistivity of 0.6729 Ω cm, mobility of 6.150 cm2 V−1 s−1 and carrier concentration of 1.508 × 1018 cm−3.

XRD, SEM, XPS studies of Sb doped ZnO films and electrical properties of its based Schottky diodes

This work presents both the morphological and structural characterizations of ZnO depending on the Sb doping and the electrical characterization of ZnO based Schottky diodes grown on ITO substrates by sol gel dip coating method. In Schottky diode fabrication, undoped and Sb doped ZnO were used, which exhibit n-type and p-type behavior, respectively. For undoped and Sb doped ZnO, Pt and Al were used as a metal contact. For the surface morphology, scanning electron microscopy (SEM) has been carried out and the surface properties that play an important role on the Schottky diode performance were characterized by SEM. X-ray diffraction (XRD) measurements revealed that crystal quality got worse and crystallite size decreased with Sb incorporation. The presence of Sb in the ZnO was confirmed by X-ray photoelectron spectroscopy (XPS). Undoped and Sb doped ZnO based Schottky diodes were fabricated and their electrical properties were carried out in dark. The diode parameters such as ideality factor (n), barrier height (φB) and series resistance (Rs) were systematically analyzed by using thermionic emission theory and Cheung’s method.

Effect of nanowires in microporous structures on the thermoelectric properties of oxidized Sb-doped ZnO film

Sb-doped ZnO thermoelectric films with microporous structures are fabricated by oxidizing evaporated Zn-Sb thin films in a leaf-like surface. High magnetic field (HMF) and Sb are employed to tune the formation of nanowires and nanorods in the microporous films and conduction type. Nanowire is formed in the film with Sb content of 3.0% and nanorod is formed with 4.6% Sb with the absence of HMF. P-type ZnO films with a wuterzite are formed. The resistivity of the films decreases by two orders of magnitude by increasing Sb content. The resistivity of films decreases 45% and 80% by forming nanowires and nanorods, respectively. The power factor of the nanorod structures increases by two orders of magnitude by comparison with others and reaches to 52.6μW/m K2. This indicates that the nanorod structures with a higher Sb content are easy to obtain stable p-type semiconductor with a higher power factor.

Sb-related defects in Sb-doped ZnO thin film grown by pulsed laser deposition

Sb-doped ZnO films were fabricated on c-plane sapphire using the pulsed laser deposition method and characterized by Hall effect measurement, X-ray photoelectron spectroscopy, X-ray diffraction, photoluminescence, and positron annihilation spectroscopy. Systematic studies on the growth conditions with different Sb composition, oxygen pressure, and post-growth annealing were conducted. If the Sb doping concentration is lower than the threshold ∼8 × 1020 cm−3, the as-grown films grown with an appropriate oxygen pressure could be n∼4 × 1020 cm−3. The shallow donor was attributed to the SbZn related defect. Annealing these samples led to the formation of the SbZn-2VZn shallow acceptor which subsequently compensated for the free carrier. For samples with Sb concentration exceeding the threshold, the yielded as-grown samples were highly resistive. X-ray diffraction results showed that the Sb dopant occupied the O site rather than the Zn site as the Sb doping exceeded the threshold, whereas the SbO related deep acceptor was responsible for the high resistivity of the samples.

Influence of molar ratio of Sb/Zn on the crystal, electrical and optical properties of Sb-doped ZnO films

Sb-doped p-type ZnO films were grown on sapphire substrate by metal organic chemical vapor deposition method. The influence of the molar ratio of Sb/Zn on the crystal, electrical and optical properties of the Sb-doped ZnO films was investigated by X-ray diffraction (XRD), Hall measurement system, optical absorption and photoluminescence spectroscopy. XRD patterns revealed all Sb-doped ZnO films were polycrystalline structures with strong c-axis orientation preferred. Electrical measurement results indicated Sb-doped ZnO films exhibited p-type electrical properties, and carrier concentrations were in the range of 10−17–10−18 cm−3. Low temperature photoluminescence measurement confirmed the existence of Sb in Sb-doped ZnO film. The photoluminescence spectrum of the Sb-doped ZnO film revealed the transition between the free electrons and acceptors peak at 3.243 eV, the acceptor-bound exciton peak at 3.319 eV and the donor-acceptor pair exciton at 3.200 eV. The thermal binding energy of the Sb accepter was estimated to be 0.19 eV.

Influence of substrate temperature on the optical properties of Sb-doped ZnO films prepared by MOCVD

The Sb-doped ZnO films were grown on c-plane sapphire by metal organic chemical vapor deposition technology with various substrate temperatures. We have examined the influence of the substrate temperature on the crystal, electrical and optical properties of the Sb-doped ZnO films. The XRD patterns indicated the undoped ZnO film and the Sb-doped ZnO films showed a strong preferred orientation toward the c-axis. Hall effects measurements revealed the Sb-doped ZnO films exhibited p-type electrical conductivity. Low temperature photoluminescence spectra confirmed the existence of Sb in ZnO films. The photoluminescence spectra of the Sb-doped ZnO films revealed the transition between the free electrons and acceptors peak at 3.243 eV, the acceptor-bound exciton peak at 3.319 eV. The thermal binding energy of the Sb accepter was estimated to be about 0.19 eV.

Spetroscopic ellipsometry study on electrical and elemental properties of Sb-doped ZnO thin films

Room-temperature spectroscopic ellipsometry data has been analyzed to determine the complex dielectric functions, ɛ(E) = ɛ1(E) + iɛ2(E) of as-deposited Sb-doped ZnO (SZO) thin films grown on n-Si(100) substrates by dual ion beam sputtering deposition system for different growth temperatures (Tg). The dielectric functions have been obtained from ellipsometry data analyses using Cody-Lorentz oscillator in the GenOsc model. A gradual reduction in the value of electron concentration and finally the conversion of doping characteristics from donor type to acceptor type was observed with the rise in Tg. This, in turn, resulted in the decline of broadening of ɛ1 peaks, and hence in the increase of excitonic lifetime. Optical band-gap energy was observed to decrease with increase in Tg from 200 to 300 °C, and then rise continuously with further increase in Tg. X-ray diffraction measurements showed that all SZO films had (002) preferred crystal orientation. Hall measurement and X-ray photoelectron spectroscopy analysis confirmed that the change in the electrical conduction from n-to p-type was due to the enhancement in the value of Sb5+/Sb3+ ratio and SbZn–2VZn complex formation in SZO films.

P-type conduction from Sb-doped ZnO thin films grown by dual ion beam sputtering in the absence of oxygen ambient

Sb-doped ZnO (SZO) thin films were deposited on c-plane sapphire substrates by dual ion beam sputtering deposition system in the absence of oxygen ambient. The electrical, structural, morphological, and elemental properties of SZO thin films were studied for films grown at different substrate temperatures ranging from 200 °C to 600 °C and then annealed in situ at 800 °C under vacuum (pressure ∼5 × 10−8 mbar). Films grown for temperature range of 200–500 °C showed p-type conduction with hole concentration of 1.374 × 1016 to 5.538 × 1016 cm−3, resistivity of 66.733–12.758 Ω cm, and carrier mobility of 4.964–8.846 cm2 V−1 s−1 at room temperature. However, the film grown at 600 °C showed n-type behavior. Additionally, current-voltage (I–V) characteristic of p-ZnO/n-Si heterojunction showed a diode-like behavior, and that further confirmed the p-type conduction in ZnO by Sb doping. X-ray diffraction measurements showed that all SZO films had (002) preferred crystal orientation. X-ray photoelectron spectroscopy analysis confirmed the formation of SbZn–2VZn complex caused acceptor-like behavior in SZO films.

Influence of in-situ annealing ambient on p-type conduction in dual ion beam sputtered Sb-doped ZnO thin films

Sb-doped ZnO (SZO) films were deposited on c-plane sapphire substrates by dual ion beam sputtering deposition system and subsequently annealed in-situ in vacuum and in various proportions of O2/(O2 + N2)% from 0% (N2) to 100% (O2). Hall measurements established all SZO films were p-type, as was also confirmed by typical diode-like rectifying current-voltage characteristics from p-ZnO/n-ZnO homojunction. SZO films annealed in O2 ambient exhibited higher hole concentration as compared with films annealed in vacuum or N2 ambient. X-ray photoelectron spectroscopic analysis confirmed that Sb5+ states were more preferable in comparison to Sb3+ states for acceptor-like SbZn-2VZn complex formation in SZO films.

P-ZnO thin film/n-Si heterojunction light-emitting diode fabricated by chemical vapor deposition and its characterization

The Sb-doped ZnO film/n-Si heterojunction is synthesized by simple chemical vapor deposition method. The quality of crystal and surface morphology of Sb-doped ZnO film are improved after annealing at 800 ℃, which exhibits effective p-type conductivity with a hole concentration of 9.56× 1017 cm-3. The properties of the p-ZnO/n-Si heterojunction photoelectric device are investigated. The resuets show that this device has good rectifier characteristics with a positive open electric of 4.0 V, and a reverse breakdown voltage of 9.5 V. The electroluminescent is realized at room temperature under the condition of forward current 45 mA. These results also confirm that the high-quality ZnO film can be prepared by the simple chemical vapor deposition method, which opens the way for simple preparation of materials applied to ZnO based opto-electronic device.

Influence of O2 pressure on the properties of heavily-doped ZnO:Sb thin films grown by pulsed laser deposition

Heavily Sb-doped ZnO films were deposited on the glass substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD) and photoelectron spectroscopy (XPS) were employed to characterize their microstructures and chemical valence states. Transmittance spectra and Hall measurements were used to evaluate their optical and electrical properties. It was found that the as-prepared ZnO:Sb thin films showed a single-hexagonal-phase structure, with the optical band gap tuning from 3.33 to 3.11 eV. The variation in the band gap was attributed to a large co-axis strain in the alloy films induced by Sb incorporation. Besides, the alloy films showed a semi-insulated characteristic with high resistivity of ~104 Ω cm, which was possibly related to a compensation of intrinsic defects.

Sb doping behavior and its effect on crystal structure, conductivity and photoluminescence of ZnO film in depositing and annealing processes

The Sb-doped ZnO (ZnO:Sb) and undoped ZnO films with wurtzite structure and (0 0 2) preferred orientation were deposited on Si(1 0 0) substrate at 550 °C. It is deduced from XRD and XPS measurements that the Sb in the as-grown ZnO:Sb has high oxidation state and dopes in the form of oxygen-rich Sb–O clusters, which results in a large inner stress and a great increase of the c-axis lattice constant. After annealing at 750 °C under vacuum, the c-axis lattice constant of the ZnO:Sb decreases sharply to near the value of ZnO bulk, the electrical properties change from n-type to p-type and the PL intensity ratio of the visible to ultraviolet emission band goes down greatly, as the Sb content increases from 0 to 2.1 at.%. EDS and XRD measurements indicate that some of Sb dopants escape from the ZnO:Sb films and the oxygen-rich Sb-O clusters vanished after the annealing process. The effect of the change in Sb doping behavior on crystal structure, conductivity and PL is discussed in detail.

Minority carrier transport in p-ZnO nanowires

In this work, we explore the minority carrier diffusion length in zinc oxide nanowires, using the electron beam-induced current technique. Systematic measurements as a function of temperature were performed on p-type, Sb-doped ZnO film, containing a 4 μm thick nanowire layer. The minority carrier diffusion length exhibits a thermally activated increase with the energy of 74±5 meV. Electron beam irradiation also causes the diffusion length increase with the activation energy of 247±10 meV, likely related to SbZn–2VZn acceptor-complex.

Photoluminescence study of Sb-doped ZnO films deposited by a closed tube CVT technique

Sb-doped ZnO film was obtained by CVT technique in a closed tube, and the temperature dependence of its photoluminescence spectrum was also investigated. The Sb-related photoluminescence peaks were observed. The peaks occurred at 3.352, 3.312, 3.240 and 3.168 eV were respectively assigned to the neutral acceptor-bound excition, free electron to acceptor transitions, and the first- and second- longitudinal optical phonon replicas emissions. The acceptor binding energy was determined to be 125 meV, aided by free electron to acceptor transition.