Sb-doped P-type ZnO Research Articles

Cation impurity-defect complex induced ferromagnetism and hopping conduction in Sb-doped ZnO synthesized under high pressure

Sb-doped p-type ZnO was synthesized using the high-pressure method with a quasi-equilibrium thermodynamic process. Room temperature ferromagnetism was observed in Sb-doped ZnO. The ferromagnetic coupling was found to be associated with zinc vacancies (VZn) induced by Sb doping, which was supported by a strong ultraviolet emission peak relevant to VZn in low temperature photoluminescence. Hall effect measurements indicated that the Sb-doped ZnO with Sb content of 3.4 at% had a hole concentration of 1.4 × 1020 cm−3 and low resistivity of 7.4 × 10−2 Ω cm. Temperature-dependent resistance measurements suggest that the electrical conduction mechanism of the Sb-doped ZnO changed from thermal activation model and nearest-neighbor hopping (NNH) conduction at high temperature to Mott variable-range hopping (VRH) and Efros–Shklovskii VRH conduction at low temperature. First-principles calculations demonstrated that the Sb impurity substituting Zn (SbZn) combines two VZn defects to form acceptor-like impurity-defect complex of SbZn–2VZn in ZnO due to the coulomb attraction. The SbZn–2VZn complex in Sb-doped ZnO are strongly correlated with ferromagnetic stability and lead to the Mott and Efro–Shklovskii VRH conduction at low temperature due to the localization of carriers at the complex impurity band.

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.

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.

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.

Fabrication of Sb-doped p-type ZnO Thin Films by Pulsed Laser Deposition

In this work, antimony (Sb)-doped p-type ZnO thin films on c-plane sapphire substrates have been fabricated by pulsed laser deposition, with Sb2O3 used as the dopant source. The effects of ambient gas or growth temperature on the fabrication process were investigated. The nitrogen ambient was found to be essential to achieve the p-type conduction. The Hall-effect measurements at room temperature indicated that the ZnO thin films doped with 3 at.% Sb and grown at 600 °C under N2 atmosphere exhibited p-type behavior with a hole concentration of 1.17×1017 cm−3, hole mobility of 0.63 cm2/V·s, and resistivity of 84.51 Ω·cm. X-ray diffraction and scanning electron microscopy revealed good crystallization and homogenous surface morphology of the ZnO:Sb thin films. The optical transmission spectrum of the ZnO:Sb thin films indicated that the energy band gap value was around 2.9 eV. Post-growth annealing at 650 oC converted the p-type conduction to n-type. This result implied that Sb-doping and annealing treatment were dominant factors determining native and extrinsic defects in the ZnO thin films, and thus controlling their electrical conductivity properties.

Sb-Doped ZnO microwires: emitting filament and homojunction light-emitting diodes

Individual Sb-doped p-type ZnO (ZnO:Sb) microwires have been synthesized, and could be used to construct wavelength-tuning emitting filaments in the visible region. Meanwhile, ZnO:Sb microwires are applied to fabricate homojunction ultraviolet light-emitting diodes.

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.

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.

Fabrication of Sb-doped p-type ZnO Thin Films by Pulsed Laser Deposition

In this work, antimony (Sb)-doped p-type ZnO thin films on c-plane sapphire substrates have been fabricated by pulsed laser deposition, with Sb2O3 used as the dopant source. The effects of ambient gas or growth temperature on the fabrication process were investigated. The nitrogen ambient was found to be essential to achieve the p-type conduction. The Hall-effect measurements at room temperature indicated that the ZnO thin films doped with 3 at.% Sb and grown at 600 °C under N2 atmosphere exhibited p-type behavior with a hole concentration of 1.17×1017 cm−3, hole mobility of 0.63 cm2/V·s, and resistivity of 84.51 Ω·cm. X-ray diffraction and scanning electron microscopy revealed good crystallization and homogenous surface morphology of the ZnO:Sb thin films. The optical transmission spectrum of the ZnO:Sb thin films indicated that the energy band gap value was around 2.9 eV. Post-growth annealing at 650 oC converted the p-type conduction to n-type. This result implied that Sb-doping and annealing treatment were dominant factors determining native and extrinsic defects in the ZnO thin films, and thus controlling their electrical conductivity properties.

ZnO homojunction UV photodetector based on solution-grown Sb-doped p-type ZnO nanorods and pure n-type ZnO nanorods

The p-type Sb-doped ZnO NRs act as one of promising candidates for electronic and optoelectronic devices in the future.

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.

A highly efficient UV photodetector based on a ZnO microwire p–n homojunction

A highly efficient ultraviolet photodetector was successfully obtained based on a Sb-doped p-type ZnO microwire p–n homojunction which consisted of a single Sb-doped p-type ZnO microwire and a single undoped ZnO microwire. The ultralong Sb-doped ZnO single crystalline microwires were synthesized via a chemical vapor deposition method. The ZnO microwire homojunction showed well-defined rectification characteristics, which indicated the p-type conductivity of the Sb-doped ZnO microwire. An ultraviolet photodetector with an external quantum efficiency of 64.5% was obtained based on the ZnO microwire p–n homojunction. The photodetector showed high wavelength selectivity with a full width at half maximum of 6 nm for the photoresponse peak located at 386 nm.

Piezotronic Effect in Solution-Grown p-Type ZnO Nanowires and Films

Investigating the piezotronic effect in p-type piezoelectric semiconductor is critical for developing a complete piezotronic theory and designing/fabricating novel piezotronic applications with more complex functionality. Using a low temperature solution method, we were able to produce ultralong (up to 60 μm in length) Sb doped p-type ZnO nanowires on both rigid and flexible substrates. For the p-type nanowire field effect transistor, the on/off ratio, threshold voltage, mobility, and carrier concentration of 0.2% Sb-doped sample are found to be 10(5), 2.1 V, 0.82 cm(2)·V(-1)·s(-1), and 2.6 × 10(17) cm(-3), respectively, and the corresponding values for 1% Sb doped samples are 10(4), 2.0 V, 1.24 cm(2)·V(-1)·s(-1), and 3.8 × 10(17) cm(-3). We further investigated the universality of piezotronic effect in the as-synthesized Sb-doped p-type ZnO NWs and reported for the first time strain-gated piezotronic transistors as well as piezopotential-driven mechanical energy harvesting based on solution-grown p-type ZnO NWs. The results presented here broaden the scope of piezotronics and extend the framework for its potential applications in electronics, optoelectronics, smart MEMS/NEMS, and human-machine interfacing.

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.

Enhanced output power using MgZnO/ZnO/MgZnO double heterostructure in ZnO homojunction light emitting diode

A diode with Sb-doped p-type ZnO, MgZnO/ZnO/MgZnO double heterostructure, and undoped n-type ZnO layers was grown on c-plane sapphire substrate by plasma-assisted molecular-beam epitaxy. Hall effect measurement showed that the top p-type Sb-doped ZnO layer has a hole concentration of 1 × 1017cm−3. Mesa geometry light emitting diodes were fabricated with Au/Ni and Au/Ti Ohmic contacts on top of the p-type and n-type layers, respectively. Ultraviolet emission was achieved, which yielded an output power of 457 nW at 140 mA. The enhancement of the output power is attributed to carrier confinement in the good-quality intrinsic layer of the double heterostructure. The spatial distribution of light emission was characterized.

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.

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.

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.

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.