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The interaction of Na impurities and O vacancies (VO) in ZnO was studied in theory and experiment. The VO facilitated substitutional Na (NaZn/NaZn-) acceptors with inhibiting interstitial Na (Nai/Nai+) donors, which may benefit the p-type conductivity. The formed (NaZn-VO)+/0 complexes induced the change of band structures of ZnO, with the broadening of gap energies and disappearance of the VO2+-related impurity level, which confirmed by the blue shift of the near-band-edge (NBE) UV emission and the decay of the visible emission in PL spectra. The strong and dominant NBE UV emission suggested acceptable luminescence behaviors of Na-doped ZnO. [ABSTRACT FROM AUTHOR]

Al-doped ZnO (AZO) thin films have been prepared by mist chemical vapor deposition and magnetron sputtering. The band gap shift as a function of carrier concentration in n-type zinc oxide (ZnO) was systematically studied considering the available theoretical models. The shift in energy gap, evaluated from optical absorption spectra, did not depend on sample preparations; it was mainly related to the carrier concentrations and so intrinsic to AZO. The optical gap increased with the electron concentration approximately as ne2/3 for ne≤4.2×1019 cm-3, which could be fully interpreted by a modified Burstein–Moss (BM) shift with the nonparabolicity of the conduction band. A sudden decrease in energy gap occurred at 5.4-8.4×1019 cm-3, consistent with the Mott criterion for a semiconductor-metal transition. Above the critical values, the band gap increased again at a different rate, which was presumably due to the competing BM band-filling and band gap renormalization effects, the former inducing a band gap widening and the latter an offsetting narrowing. The band gap narrowing (ΔEBGN) derived from the band gap renormalization effect did not show a good ne1/3 dependence predicated by a weakly interacting electron-gas model, but it was in excellent agreement with a perturbation theory considering different many-body effects. Based on this theory a simple expression, ΔEBGN=Ane1/3+Bne1/4+Cne1/2, was deduced for n-type ZnO, as well as p-type ZnO, with detailed values of A, B, and C coefficients. An empirical relation once proposed for heavily doped Si could also be used to describe well this gap narrowing in AZO. [ABSTRACT FROM AUTHOR]

(Zn,Al)O thin films have been prepared by a dc reactive magnetron sputtering system with the Al contents in a wide range of 0–50 at. %. The structural, optical, and electrical properties of (Zn,Al)O films were detailedly and systematically studied. The amount of Al in the film was nearly the same as, but often lower than, that in the sputtering target. The growth rate of films monotonically decreased as the Al content increased. In a low Al content region (<10 at. %), Al-doped ZnO (AZO) thin films could be obtained at 400 °C in an Ar–O2 ambient with good properties. The optimal results of n-type AZO films were obtained at an Al content of 4 at. %, with low resistivity ∼10-4 Ω cm, high transmittance ∼90% in the visible region, and acceptable crystal quality with a high c-axis orientation. The band gap could be widened to 3.52 eV at 4 at. % Al due to the Burstein-Moss shift [E. Burstein, Phys. Rev. 93, 632 (1954)] modulated by many-body effects. An appropriate Al-doping concentration served effectively to release the residual, compressive stress in film, which may be the reason for the improvement in film stability and the increment in grain size as well. In a medium Al content region (10–30 at. %), however, the film quality was degraded, which was presumably due to the formation of clusters or precipitates in the grains and boundaries. Besides the (002) plane, other diffraction peaks such as (100) and (101) planes of ZnO were observed, but the (Zn,Al)O films still exhibited a single-phase wurtzite ZnO structure. An intragrain cluster scattering mechanism was proposed to interpret the reduction of carrier mobility in films with the Al contents in the 7–20 at. % region. The solubility limit of Al in ZnO film was identified to be in the 20–30 at. % range, much higher than the thermodynamic solubility limit of 2–3 at. % in ZnO. In a high Al content region (>=30 at. %), there were distinct observations for (Zn,Al)O films. As the Al content was 30 at. %, the film appeared in a two-phase nature with ZnO hexagonal and Al2O3 rhombohedral structures. At the 50 at. % Al content, the matrix of the (Zn,Al)O film was Al2O3, and no evident trace of wurtzite ZnO was observed. The electrical and optical properties for both cases were also very different from those at the Al contents below 30 at. %. [ABSTRACT FROM AUTHOR]

Glitch (sudden spin-up) is a common phenomenon in pulsar observations. However, the physical mechanism of glitch is still a matter of debate because it depends on the puzzle of pulsar's inner structure, i.e. the equation of state of dense matter. Some pulsars (e.g. Vela like) show large glitches (Δν/ν ∼ 10−6) but release negligible energy, whereas the large glitches of AXPs/SGRs (anomalous X-ray pulsars/soft gamma repeaters) are usually (but not always) accompanied with detectable energy releases manifesting as X-ray bursts or outbursts. We try to understand this aspect of glitches in a starquake model of solid quark stars. There are two kinds of glitches in this scenario: bulk-invariable (type I) and bulk-variable (type II) ones. The total stellar volume changes (and then energy releases) significantly for the latter but not for the former. Therefore, glitches accompanied with X-ray bursts (e.g. that of AXP/SGRs) could originate from type II starquakes induced probably by accretion, while the others without evident energy release (e.g. that of Vela pulsar) would be the result of type I starquakes due to, simply, a change of stellar ellipticity. [ABSTRACT FROM PUBLISHER]

In this Letter, we present the size effects on chargeconductionin InN nanowires by comprehensive transport studies supported by theoreticalanalysis. A consistent model for highly degenerate narrow gap semiconductornanowires is developed. In contrast to common knowledge of InN, thereis no evidence of an enhanced surface conduction, however, high intrinsicdoping exists. Furthermore, the room-temperature resistivity exhibitsa strong increase when the lateral size becomes smaller than 80 nmand the temperature dependence changes from metallic to semiconductor-like.This effect is modeled by donor deactivation due to dielectric confinement,yielding a shift of the donor band to higher ionization energies asthe size shrinks. [ABSTRACT FROM AUTHOR]

ZnO is attracting intensive attention for its versatile applications in transparent electronics, UV emitter, piezoelectric devices, chemical sensor and spin electronics. As one of the direct wide band gap semiconductors, it has advantages over GaN due to its larger exciton binding energy, better lattice match on heteroepitaxial growth and availability of single crystal substrate. Large effort has been invested in the growth of nanostructured ZnO to explore its potentials for nanoscale device applications. ZnO nanobelts, nanowires, nanorings, and nanohelixes demonstrate the diversity of ZnO nanostructures family. This review presents recent research on ZnO nanostructures. Issues of synthesis methods, optical, electrical, gas sensing and magnetic properties are summarized. These progresses constitute the basis for developing future applications in nanoscale electronics, optoelectronics, chemical sensor and spintronics. [ABSTRACT FROM AUTHOR]

Reproducible and stable p-type ZnO thin films have been prepared by the N–Al codoping method. Secondary ion mass spectroscopy measurements demonstrate that N and Al are incorporated into ZnO. The resistivity, carrier concentration, and Hall mobility are typically of 50–100 Ωcm, 1×1017–8×1017 cm−3, and 0.1–0.6 cm2/Vs, respectively, for the N–Al codoped p-type ZnO films. Hall measurement, X-ray diffraction, and optical transmission were carried out to investigate the changes of the properties with the storage period. Results show that the p-type characteristics of the N–Al codoped ZnO films are of acceptable reproducibility and stability. In addition, the N–Al codoped p-type ZnO films have good crystallinity and optical quality. The properties are time independent. [ABSTRACT FROM AUTHOR]

Background Blood stem cells collected by apheresis are largely mononuclear cells in nature, so manipulation of blood stem-cell components freequently requires more time and reagents than for a marrow harvest. Reducing the nucleated cell number in mobilized blood stemcell collections, while preserving hematopoietic progenitor content, would make such manipulations simpler and less costly, but only if debulking procedures were not complex. Methods We evaluated separation of light-density cells and enrichment of CD34 + cells from mobilized peripheral blood stem-cell collections by density gradient centrifugation over buoyant density solution 60 (BDS 60) in a single, closed vessel. Results Fifteen apheresis products from five normal volunteers and eight cancer patients contained 3.44 (range, 1.19-5.51) × 10 10 nucleated cells. Following processing and washing, there was a median 29% recovery of nucleated cells, 79% recovery of CD34 + cells, 2.49-fold enrichment of CD34 + cells, 0.96-log depletion of CD3 + cells, 0.48-log depletion of CD56 + cells, and 0.72-log depletion of CD19 + cells. Results of processing were affected by the variability in composition of the apheresis products. The enrichment of CD34 + cells varied by donor type, and there was a logarithmic relationship between the preprocessing percentage of CD19 + cells and the log reduction in CD19 + cells. Recovery of cells after thawing and washing was acceptable for processed cells cryopreserved at concentrations over the range of 0.01-1.5 × 10 8 /mL. Discussion These results demonstrate a simple method by which an apheresis product of 1-5 × 10 10 cells can be debulked effectively in a single, closed vessel. [ABSTRACT FROM AUTHOR]

Quasialigned, single-crystal Zn1-xMgxO (x=0–0.32) nanorods were synthesized on Si substrates by thermal evaporation. Zn1-xMgxO nanorods grew along the [0001] crystal direction and had uniform hexagonal planes with diameters of 420–120 nm. The predominant ultraviolet luminescence could be tuned from 379 (x=0) to 305 nm (x=0.32) at room temperature. This blueshift indicated the band gap engineering in Zn1-xMgxO nanorods. Temperature-dependent photoluminescence was used to illustrate the free-exciton emission from Zn1-xMgxO nanorods. The exciton binding energy decreased from 59 (x=0) to 49 meV (x=0.18) and then increased to 54 meV (x=0.32). [ABSTRACT FROM AUTHOR]

ZnO homojunction light-emitting diodes (LEDs), comprised of N–Al codoped p-type ZnO and Al-doped n-type ZnO layers, were fabricated on Si substrates with homobuffer layers. The current-voltage measurements showed typical diode characteristic with a threshold voltage of about 3.3 V. The electroluminescence (EL) bands at 110 K consisted of a near-band-edge emission at 3.18 eV and a deep level emission at 2.58 eV. The EL emissions were assigned as radiative recombinations, presumably of donor-acceptor pairs, in the p-type layer of the LED. The quenching of EL with temperature was attributed to the degradation of p-type conducting of the ZnO:(N,Al) layer. [ABSTRACT FROM AUTHOR]

Transparent conducting Al-doped Zn1-xMgxO thin films were grown on glass substrates by chemical vapor deposition. The resistivity could be lowered to 10-3 Ω cm with optical transmittance above 85% in visible regions. The influence of carrier concentration on band-gap shift in Zn1-xMgxO alloys was systematically studied. The shift of energy gap could be fully explained by the Fermi-level band filling and band-gap renormalization effects. As the Mg content increased, the electron effective masses in Zn1-xMgxO (x=0–0.21) alloys increased from 0.30m0 to 0.49m0. The Al-doping efficiency was reduced with the increase in alloy composition. [ABSTRACT FROM AUTHOR]

Li-doped ZnO films were prepared by pulsed laser deposition. The carrier type could be controlled by adjusting the growth conditions. In an ionized oxygen atmosphere, p-type ZnO was achieved, with the hole concentration of 6.04 × 1017 cm-3 at an optimal Li content of 0.6 at. %, whereas ZnO exhibited n-type conductivity in a conventional O2 growth atmosphere. At a Li content of more than 1.2 at. % only high-resistivity ZnO was obtained. The amount of Li introduced into ZnO and the relative concentrations of such defects as Li substitutions and interstitials could play an important role in determining the conductivity of films. [ABSTRACT FROM AUTHOR]

Electrical characteristics have been studied for ZnO p-n and p-i-n homojunctions, with optimization of device structures for improved performance. Capacitance-voltage measurements confirm the formation of abrupt junctions. The current-voltage characteristics exhibit their inherent electrical rectification behavior. The p-ZnO:(N,Al)/n-ZnO:Al homojunctions fabricated on sapphire substrates combining with the intrinsic ZnO buffer layer have acceptable p-n diode characteristics, with the forward turn-on voltage of 1.4 V and the reverse breakdown voltage of 5.3 V. By introduction of an intrinsic (Zn,Cd)O layer, the resultant p-ZnO:(N,Al)/i-(Zn,Cd)O/n-ZnO:Al homojunction exhibits a high reverse breakdown voltage of ∼18 V. [ABSTRACT FROM AUTHOR]

Self-assembled ZnO quantum dots (QDs) were achieved by a vapor phase transport process. ZnO nanodots were naturally formed on solid substrates in the Volmer-Weber growth mode. Size control of nanodots could be readily realized by varying the growth time. The as-prepared ZnO QDs are of high quality and very stable after formation. The blueshift of band gap energies derived from quantum confinement effects was confirmed by optical absorption spectra. Photoluminescence spectra revealed the tunable behavior of ultraviolet luminescence due to exciton localization. The realization of size-tuned color from ZnO QDs makes them more promising for practical applications. [ABSTRACT FROM AUTHOR]

A Li–N dual-acceptor doping method has been developed to prepare p-type ZnO thin films by pulsed laser deposition. The lowest room-temperature resistivity is found to be ∼0.93 Ω cm, much lower than that of Li or N monodoped ZnO films. The p-type conductivity of ZnO:(Li,N) films is very reproducible and stable, with acceptable crystal quality. The acceptor activation energy in ZnO:(Li,N) is about 95 meV. ZnO-based homostructural p-n junctions were fabricated by depositing an n-type ZnO:Al layer on a p-type ZnO:(Li,N) layer, confirmed by secondary ion mass spectroscopy. The current-voltage characteristics exhibit their inherent rectifying behaviors. [ABSTRACT FROM AUTHOR]

A vapor phase transport growth process has been developed to synthesize ZnO quantum dots (QDs) on Si substrates. The characteristics were investigated for as-prepared ZnO QDs without any additional treatment. The formation of ZnO QDs with 6 nm in height and 15 nm in diameter is confirmed by scanning electron microscope and atomic force microscopy. Room-temperature photoluminescence reveals that the as-prepared ZnO QDs exhibit a predominant ultraviolet emission at 3.32 eV while the low energy defect-related blue-green emission is significantly quenched. The band gap of ZnO QDs is determined to be 3.41 eV, which evidently indicates the quantum confinement effects. [ABSTRACT FROM AUTHOR]

p-type ZnO thin films have been realized by the In–N codoping method. Secondary ion mass spectroscopy revealed that the nitrogen incorporation was enhanced by the presence of indium in ZnO. The as-grown In–N codoped ZnO film shows acceptable p-type behavior at room temperature with high film quality. A conversion from p-type conduction to n type in a range of temperature was confirmed by Hall effect measurement. The lowest reliable room-temperature resistivity was found to be 3.12 Ω cm with a carrier concentration of 2.04×1018 cm-3 and a Hall mobility of 0.979 cm2 V-1 S-1. The p-type behavior is stable. [ABSTRACT FROM AUTHOR]

We propose a specifically designed structure to fabricate thin-film transistors using amorphous indium-gallium-zinc-oxide (a-IGZO) films as the active channel layers. The I-shaped gate electrode is employed to define the channel width, reducing overlaps between the gate and source/drain electrodes. The devices with such a structure exhibit acceptable electrical performance and stability after annealing treatment. The XPS data show that the as-deposited a-IGZO film has not a very dense structure that may induce shallow traps. A shallow trap model is proposed to explain the large threshold voltage shifts of the as-deposited device. Annealing treatment can eliminate these shallow traps and improve the device stability. [ABSTRACT FROM AUTHOR]

In clean tunneling junctions (TJs), the momentum parallel to the barrier is conserved in the tunneling process. We predict that this phenomenon can be observed in a TJ between a ferromagnet (FM) and a topological insulator (TI). The FM possesses spin-polarized electron states, while the TI has spin-momentum locked electron states. The tunneling probability is determined by the spin-matrix element between these electron states and leads to the injection of electrons into the TI with finite momentum parallel to the topological surface state. Due to the spin polarization of the electrons in the FM, the resulting current in the TI is not isotropic. The magnitude of the current is calculated quantitatively in terms of the ferromagnetic polarization and should be experimentally detectable using only an electrical setup. [ABSTRACT FROM AUTHOR]

Pulsar-like compact stars provide us a unique laboratory to explore properties of dense matter at supra-nuclear densities. One of the models for pulsar-like stars is that they are totally composed of "strangeons", and in this paper, we studied the pulsar glitches in a strangeon star model. Strangeon stars would be solidified during cooling, and the solid stars would be natural to have glitches as the result of starquakes. Based on the starquake model established before, we proposed that when the starquake occurs, the inner motion of the star which changes the moment of inertia and has impact on the glitch sizes, is divided into plastic flow and elastic motion. The plastic flow which is induced in the fractured part of the outer layer, would move tangentially to redistribute the matter of the star and would be hard to recover. The elastic motion, on the other hand, changes its shape and would recover significantly. Under this scenario, we could understand the behaviors of glitches without significant energy releasing, including the Crab and the Vela pulsars, in an uniform model. We derive the recovery coefficient as a function of glitch size, as well as the time interval between two successive glitches as the function of the released stress. Our results show consistency with observational data under reasonable ranges of parameters. The implications on the oblateness of the Crab and the Vela pulsars are discussed. [ABSTRACT FROM AUTHOR]

p-type ZnO thin films have been realized by the N–Al co-doping method. Secondary ion mass spectroscopy demonstrated that the N incorporation was enhanced evidently by the presence of Al in ZnO. The lowest room-temperature resistivity was found to be 57.3 Ω cm with a Hall mobility of 0.43 cm2/V s and carrier concentration of 2.25×1017 cm-3 for the N–Al co-doped p-type ZnO film deposited on glass substrate. The results were much better than those for the N-doped p-type ZnO. Moreover, the co-doped film possesses a good crystallinity with c-axis orientation and a high transmittance (90%) in the visible region. [ABSTRACT FROM AUTHOR]

A correction is presented to "Rational synthesis and tunable optical properties of quasialigned Zn(sub 1-x)Mg(sub x) nanorods," which appeared in Applied Physics Letters no. 91 in 2007.

The frequency evolution behavior of radio pulse profiles is an important clue for the radiation mechanism of a pulsar. Combined with the latest results of the European Pulsar Network and the Australia Telescope National Facility data, we systematically study the evolution of W50 (the full width of the pulse profile at 50% of the pulsar amplitude) for 74 pulsars with frequencies from tens to thousands of megahertz. We find that 71 pulsars show "absorption" features, which indicates that the absorption is an universal phenomenon in the pulsar population and independent of the type of pulsar profile. It is found that for most pulsars, the absorption features appear in the frequency range of 100–800 MHz, and the evolution trend of W50 at frequencies less than ∼100 MHz and larger than ∼800 MHz can be described as a power-law function.We quantify the absorption intensity and analyze the correlation between the absorption intensity and the pulsar parameters (such as the spin period, magnetic field, and age of the pulsar). It is found that there is no direct correlation between them. Our results will provide good samples and clues for the study of the physical mechanism of the absorption phenomenon. [ABSTRACT FROM AUTHOR]

We present radio observation of a millisecond pulsar PSR J0621+1002 using the Five-hundred-meter Aperture Spherical radio Telescope. The pulsar shows periodic pulse intensity modulations for both the first and the third pulse components. The fluctuation spectrum of the first pulse component has one peak of 3.0 ± 0.1 pulse periods, while that of the third pulse component has two diffused peaks of 3.0 ± 0.1 and 200 ± 1 pulse periods. The single pulse timing analysis is carried out for this pulsar and the single pulses can be divided into two classes based on the post-fit timing residuals. We examined the achievable timing precision using only the pulses in one class or bright pulses. However, the timing precision improvement is not achievable. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) was utilized to measure the valence band offset (ΔEV) of the TiZnSnO (TZTO)/Si heterojunction. TZTO films were deposited on Si (100) substrates using magnetron sputtering at room temperature. By using the Zn 2p3/2 and Sn 3d5/2 energy levels as references, the value of ΔEV was calculated to be 2.69 ± 0.1 eV. Combining with the experimental optical energy band gap of 3.98 eV for TZTO extracted from the UV-vis transmittance spectrum, the conduction band offset (ΔEC) was deduced to be 0.17 ± 0.1 eV at the interface. Hence, the energy band alignment of the heterojunction was determined accurately, showing a type-I form. This will be beneficial for the design and application of TZTO/Si hybrid devices. [ABSTRACT FROM AUTHOR]

We have investigated the influence of ZnO orientation on the valence band offset (ΔEV) of Mg0.2Ni0.8O(111)/ZnO (1120) and Mg0.2Ni0.8O(111)/ZnO(0002) heterostructures by x-ray photoelectron spectroscopy. Combining with the experimental optical energy band gap extracted from UV-vis transmittance spectra, the energy band alignment at the interfaces has been determined. The ΔEV has been found to be 1.8 ± 0.1 eV and 1.4 ± 0.1 eV for Mg0.2Ni0.8O(111)/ZnO (1120) and Mg0.2Ni0.8O(111)/ZnO(0002), respectively. Both the heterostructures show type-II band configurations with conduction band offsets (ΔEC) of 2.4 ± 0.1 eV and 2.0 ± 0.1 eV, respectively. The ZnO orientation correlated electronic structure in p-Mg0.2Ni0.8O/n-ZnO interfaces can be explained well by the effect of spontaneous polarization in ZnO. Furthermore, the results offer opportunity that desired band offsets in MgxNi1-xO/ZnO heterostructures can be obtained by appropriately adjusting Mg composition. [ABSTRACT FROM AUTHOR]

The microstructure and crystal orientations of polycrystalline films crucially affect the properties and performance of the films. Controlling preferred orientations (PO) and related film morphology are necessary to obtain the desirable properties. In this paper, we demonstrate a rational and effective route toward the realization of non-polar p-type ZnO thin film with surface texture on quartz substrate through Mn-Na codoping. It is uncovered experimentally and theoretically that mono-doping of Mn creates opportunity to realize PO from polar (c-axis) to non-polar ([formula], [formula], and [formula]) changing. With Mn-Na codoping, an acute modulation of the growth behavior and electrical conductivity of the film have been revealed, leading to weak p-type non-polar Zn0.94Mn0.05Na0.01O (ZMNO) texture. The dominant mechanism for the non-polar self-texture in the current paper is deliberately elucidated as resulting from the interplane surface diffusion with the cooperative effect of impurity dopants. The ZMNO films exhibit p-type conduction with hole concentration of 9.51 × 1015-1.86 × 1017 cm-3 and enhanced room temperature (RT) ferromagnetism possessing a saturation magnetization (Ms) of 1.52 μB/Mn. The results have potential applications in development of non-polar optoelectronic devices such as lighting emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

Dislocations in the ZnMgO pleated nanosheets were observed from high-resolution transmission electron microscopy (TEM). The Burgers vector was identified as [formula] from the Fourier filtered TEM images. Raman spectra revealed that there were microstructure defects in the ZnMgO nanosheets with the increasing Mg content. The incorporation of the Mg impurities in the ZnMgO nanosheets may promote the congregation of oxygen vacancies and thus facilitate the generation of dislocations. The oxygen deficiency as well as surface dislocations played an important role in determining the optical properties of ZnMgO pleated nanosheets. [ABSTRACT FROM AUTHOR]

p-type ZnO thin films have been fabricated by In and N codoping. The carrier type in the In–N codoped ZnO can be controlled by adjusting the growth conditions and good p-type conductivity is obtained at temperatures between 490 and 580 °C. The p-type behavior is improved when a buffer layer is used. The lowest reliable room temperature resistivity is found to be 7.85 Ω cm in the presence of a buffer layer. The ZnO-based homostructural p-n junctions comprising a n-ZnO:In layer on a p-ZnO:(In,N) layer on a buffer layer display apparent electrical rectification in the authors’ repeated measurements. [ABSTRACT FROM AUTHOR]

We investigate photoluminescence from reproducible Li-doped p-type ZnO thin films prepared by dc reactive magnetron sputtering. The LiZn acceptor state, with an energy level located at 150 meV above the valence band maximum, is identified from free-to-neutral-acceptor transitions. Another deeper acceptor state located at 250 meV emerges with the increased Li concentration. A broad emission centered at 2.96 eV is attributed to a donor-acceptor pair recombination involving zinc vacancy. In addition, two chemical bonding states of Li, evident in x-ray photoelectron spectroscopy, are probably associated with the two acceptor states observed. [ABSTRACT FROM AUTHOR]

Ga-doped ZnO (GZO)/graphene multilayer film was fabricated on the polyethylene terephthalate substrate at room temperature. The obtained GZO/graphene multilayer showed a transparence of 75% at 550nm and a sheet resistance of 721Ω/sq. Our findings indicate that the graphene intermediate layer plays a critical role in improving the conductivities of GZO. Under a tensile strain, the sheet resistance of the GZO electrode without graphene exhibited a sharp increase owing to the plenty of cracks formed in the GZO layer. In contrast, the GZO/graphene multilayer displayed a relatively stable and low resistance during the tensile deformation due to the excellent mechanical and electrical stabilities of the graphene. [ABSTRACT FROM AUTHOR]

High-resistive Zn0.95Mn0.05O and weak p-type nonpolar-oriented Zn0.94Mn0.05Na0.01O thins films were grown on quartz by pulsed laser deposition. Both samples exhibit room temperature ferromagnetism while with Mn-Na codoping, the saturation magnetic moment is greatly enhanced. It is revealed that the doped Mn impurities are substitutionally incorporated into the ZnO host. Magnetic anisotropy was also observed in the Zn0.94Mn0.05Na0.01O film, which is the indication for intrinsic ferromagnetism. The first-principles calculations reveal that codoping of Na in Zn0.94Mn0.05Na0.01O changes the antiferromagnetic interaction to ferromagnetic due to the hybridization between spin-split delocalized Mn 3d and shallow acceptor states of Na 2p, thereby enhancing the ferromagnetism. [ABSTRACT FROM AUTHOR]

A correction to the article "Identification of acceptor states in Li-doped p-type ZnO thin films" that was published in a previous issue is presented.

Nonpolor a-plane and polar c-plane ZnO thin films were prepared on r-plane sapphire and quartz substrates, respectively. The electronic structure of the interface between subsequently fabricated NiO/ZnO heterojunctions has been investigated by x-ray photoelectron spectroscopy measurements and the band offsets are determined together with information yielded from UV-vis transition spectra. It is found that a type-II band alignment forms at the interface for both the samples. The revealed ZnO-orientation dependent band offsets are analyzed and are attributed mainly due to the variations in internal electric field arose from spontaneous polarization effect. The accurate determination of the band alignment is important for the design and application of NiO/ZnO based hybrid devices. [ABSTRACT FROM AUTHOR]

The authors report on reproducible growth of ZnMgO quantum dots (QDs) by a metal organic chemical vapor deposition method. Mg is introduced into ZnO QDs, as confirmed by x-ray photoelectron spectroscopy and photoluminescence measurements. The size, density, and optical band gap of ZnMgO QDs can be well controlled by simply modulating the growth parameters. [ABSTRACT FROM AUTHOR]

We report on intrinsic p-type ZnO thin films by plasma-assisted metal-organic chemical vapor deposition. The optimal results give a resistivity of 12.7 Ω cm, a Hall mobility of 2.6 cm2/V s, and a hole concentration of 1.88×1017 cm-3. The oxygen concentration is increased in the intrinsic p-type ZnO, compared with the n-type layer. Two acceptor states, with the energy levels located at 160 and 270 meV above the valence band maximum, are identified by temperature-dependent photoluminescence. The origin of intrinsic p-type behavior has been ascribed to the formation of zinc vacancy and some complex acceptor center. [ABSTRACT FROM AUTHOR]

We report a breakthrough in fabricating ZnO homojunction light-emitting diode by metal organic chemical vapor deposition. Using NO plasma, we are able to grow p-type ZnO thin films on n-type bulk ZnO substrates. The as-grown films on glass substrates show hole concentration of 1016–1017 cm-3 and mobility of 1–10 cm2 V-1 s-1. Room-temperature photoluminescence spectra reveal nitrogen-related emissions. A typical ZnO homojunction shows rectifying behavior with a turn-on voltage of about 2.3 V. Electroluminescence at room temperature has been demonstrated with band-to-band emission at I=40 mA and defect-related emissions in the blue-yellow spectrum range. [ABSTRACT FROM AUTHOR]

Li-doped, p-type ZnO thin films have been realized via dc reactive magnetron sputtering. An optimized result with a resistivity of 16.4 Ω cm, Hall mobility of 2.65 cm2/V s, and hole concentration of 1.44×1017 cm-3 was achieved, and electrically stable over a month. Hall-effect measurements supported by secondary ion mass spectroscopy indicated that the substrate temperature played a key role in optimizing the p-type conduction of Li-doped ZnO thin films. Furthermore, ZnO-based p-n homojunction was fabricated by deposition of a Li-doped p-type ZnO layer on an Al-doped n-type ZnO layer. [ABSTRACT FROM AUTHOR]

The valence band structures of Al–N-codoped [ZnO:(Al, N)] and N-doped (ZnO:N) ZnO films were studied by normal and soft x-ray photoelectron spectroscopy. The valence-band maximum of ZnO:(Al, N) shifts up to Fermi energy level by about 300 meV compared with that of ZnO:N. Such a shift can be attributed to the existence of a kind of Al–N in ZnO:(Al, N), as supported by core level XPS spectra and comparison of modified Auger parameters. Al–N increased the relative quantity of Zn–N in ZnO:(Al, N), while N–N decreased that of Zn–N in ZnO:N. [ABSTRACT FROM AUTHOR]

ZnO p-n homojunctions were fabricated on quartz substrates by depositing Al-doped n-type ZnO layer on Al–N-co-doped p-type ZnO layer through reactive magnetron sputtering. In/Zn metal contacts to as-grown ZnO show ohmic behavior, and the ohmic contacts can be improved by annealing in an Ar ambient. The optimal annealing temperatures for Al–N-co-doped ZnO and Al-doped ZnO are 550 °C and 600 °C, respectively. The p-n junction characteristic is confirmed by current-voltage measurements. The turn-on voltage is 2 V, with a low leakage current under reverse bias. Series resistances of the ZnO p-n junctions can be lowered by optimizing the annealing temperature, increasing the grain size of the ZnO, or increasing the hole concentration of the p layer. [ABSTRACT FROM AUTHOR]

A correction to the article "ZnO light-emitting diode grown by plasma-assisted metal organic chemical vapor deposition," that was published online on April 20, 2009 is presented.