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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]

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]

Bilayer films consisting of Ga-doped ZnO (GZO) and Cu layers were grown at room temperature by magnetron sputtering. The structural, electrical, and optical properties of GZO/Cu bilayer films were investigated in detail. The crystallinity and transparent-conductive properties of the films were correlated with the Cu layer thickness. The GZO/Cu bilayer film with the Cu layer thickness of 7.8 nm exhibited a low resistivity of 7.6×10-5 Ω cm and an average visible transmittance of 74%. The reflectance was up to 65% in the near-infrared region for this film. The transparent conductive and near-infrared reflective GZO/Cu bilayer films could be readily deposited at room temperature. The GZO/Cu bilayer films were thermally stable when annealed at temperatures as high as 500 °C. [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]

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]

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]

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]

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]

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]

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]

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]