H. P. He

Temperature-dependent photoluminescence of quasialigned Al-doped ZnO nanorods

Temperature-dependent photoluminescence (PL) properties of quasialigned Al-doped ZnO nanorods grown by thermal evaporation method were investigated. The ionization energy of the Al donor was determined to be ∼90meV. A PL peak at 3.315eV was observed at low temperature and was tentatively related to excitons bound to surface defects. The emission, along with its first longitudinal optical phonon replica, persists up to room temperature and dominates the near band edge (NBE) emission of the nanorods. The doping of Al results in a redshift of ∼0.04eV of the room-temperature NBE emission of the ZnO nanorods.

Strain and its effect on optical properties of Al-N codoped ZnO films

The dependence of lattice strain in Al-N codoped p-type ZnO films on Al content and growth temperature was investigated. With increasing Al content, the compressive strain in the film first increases and then decreases. We suggest that the strain decrease is due to the occupation of more substitutional sites by Al at relatively high Al content, which partially compensates the compressive strain. Reversion of conduction type at high Al content and high temperature was also observed. By studying the strain and electrical properties of the codoped films, we conclude that ZnO film should be grown at intermediate temperatures and with low Al content to achieve both good p-type conduction and reasonable crystal quality. The compressive strain results in increase of the optical band gap, and a linear relationship between them was obtained.

Phosphorus Doped Zn1-xMgxO Nanowire Arrays

We demonstrate the growth of phosphorus doped Zn(1-x)Mg(x)O nanowire (NW) using pulsed laser deposition. For the first time, p-type Zn(0.92)Mg(0.08)O:P NWs are likely obtained in reference to atomic force microscopy based piezoelectric output measurements, X-ray photoelectron spectroscopy, and the transport property between the NWs and a n-type ZnO film. A shallow acceptor level of approximately 140 meV is identified by temperature-dependent photoluminescence. A piezoelectric output of 60 mV on average has been received using the doped NWs. Besides a control on NW aspect ratio and density, band gap engineering has also been achieved by alloying with Mg to a content of x = 0.23. The alloyed NWs with controllable conductivity type have potential application in high-efficiency all-ZnO NWs based LED, high-output ZnO nanogenerator, and other optical or electrical devices.

Na doping concentration tuned conductivity of ZnO films via pulsed laser deposition and electroluminescence from ZnO homojunction on silicon substrate

The conduction types of Na-doped ZnO films with different Na contents were investigated by repeated Hall-effect measurements and rectification behaviour of ZnO : Al/ZnO : Na homojunctions. A p-type ZnO : Na film with a resistivity of 13.8–19 Ω cm, Hall mobility of 0.12–1.42 cm2 V−1 s−1 and hole concentration of 4.78 × 1017–4.66 × 1018 cm−3 was achieved, and it was electrically stable over 9 months. The effect of the Na concentration on the conductivity of ZnO films was discussed tentatively from the results of x-ray diffraction and Hall-effect measurements as well as from the viewpoint of Madelung energy. Electroluminescence was obtained at 160 K from the optimized p–n homojunction on the silicon substrate.

Effect of Mg content on structural, electrical, and optical properties of Li-doped Zn1-xMgxO thin films

The authors have grown Li-doped p-type ZnMgO films on glass substrates with different Mg contents (11–28at.%) by pulsed laser deposition. Hall measurements suggest that the resistivity increases with Mg concentration. Acceptor levels related to LiZn located at about 150 and 174meV above the valence band maximum were discriminated in photoluminescence spectra for Li-doped Zn0.89Mg0.11O and Zn0.72Mg0.28O films, respectively. The conversion of donor-acceptor pair to a free-to-neutral-acceptor (e,A0) transition was also observed in Zn0.89Mg0.11O:Li film. The optical band gap and the acceptor binding energy increase with increase of Mg content in the films, which leads to reduction in the hole concentration and increase in the resistivity.

Photoluminescence properties of quasialigned ZnCdO nanorods

We report on the photoluminescence (PL) properties of quasialigned ZnCdO single-crystal nanorods prepared by thermal evaporation of Zn and CdCl2 on a Si substrate using Au as a catalyst. The temperature-dependent PL spectra of the ZnCdO nanorods show that each spectrum displays an intense near-band-edge (NBE) emission around 3.1eV, as well as a weak defect-related band around 2.5eV. At low temperatures, the NBE band consists of three peaks at 3.23, 3.16, and 3.06eV. From time-integrated and time-resolved PL analyses, we suggest that the peak at 3.06eV is associated with carriers localized at potential minima induced by the Cd spatial inhomogeneous distribution in ZnCdO alloys. The peak at 3.16eV is attributed to the excitonic emission of ZnCdO, while the peak at 3.23eV is ascribed to bound excitons in ZnO.

Mechanism of Na-doped p-type ZnO films: Suppressing Na interstitials by codoping with H and Na of appropriate concentrations

Hydrogen is codoped with sodium into ZnO films. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy indicate that the Na concentration decreases as the substrate temperature increases. Hall-effect tests reveal a transition from n-type to p-type conduction when the growth temperature increases, which is explained by the suppression of Na interstitials by codoping with H and Na of appropriate concentrations. An insulating intended Na–H codoped sample shows reduced resistivity and p-type conductivity after annealing at 550 °C, which may be due to dissociation of NaZn–H complexes. The realization of p-type ZnO by Na–H codoping may explain the discrepancies in behavior of Na in ZnO and suggests the potential of Na–H codoping method [E.-C. Lee and K. J. Chang, Phys. Rev. B 70, 115210 (2004)].

Mesoporous silica nanoparticles with manipulated microstructures for drug delivery.

A range of mesoporous silica nanoparticles (MSNs) with controlled microstructural characteristics were successfully prepared via the binary surfactant templated synthesis approach with varied concentration of triblock copolymer Pluronic F127. The relationship between the MSNs structural evolution and the surfactant concentration was extensively discussed. Ibuprofen (IBU) was loaded as drug model to uncover the in vitro drug releasing kinetics. It was found that the quantity of the drug loaded mainly depended on the specific surface area, while the drug releasing rate was dominantly determined by the length and curvature of the mesopores. This study has uncovered the core influential factors of MSNs system on its drug releasing properties, and thus demonstrated a facile approach to prepare MSNs with manipulated structural characteristics for drug delivery applications.

Synthesis and characterization of quasi-aligned ZnCdO nanorods

Quasi-aligned ZnCdO single-crystal nanorods were prepared for the first time by using thermal evaporation of Zn and CdCl2 on a Si substrate with the presence of Au catalyst. The maximum Cd content was up to about 16.7at.%, which was significantly larger than the thermodynamic solid solubility limits. The ZnCdO nanorods have uniform flat hexagonal crystallographic planes with diameters of about 150nm. Notably, with the Cd content increasing, the ultraviolet near-band-edge emission was redshifted to 407nm(3.04eV) from 386nm(3.21eV). The direct modulation of the band gap caused by Cd substitution is responsible for the redshift. The possible growth mechanism of the ZnCdO nanorods was discussed.

Plasma-free nitrogen doping and homojunction light-emitting diodes based on ZnO

The authors develop a plasma-free metalorganic chemical vapour deposition method to grow N-doped p-type ZnO films. The incorporation of the N acceptor and the corresponding change in the Fermi level are well confirmed by x-ray photoelectron spectroscopy. Temperature-dependent photoluminescence reveals the acceptor-related emissions, namely, neutral acceptor-bound exciton and probably donor–acceptor pair transition. In addition, typical rectifying I–V characteristics and room-temperature electroluminescence from ZnO homojunction light-emitting diodes are demonstrated.