Ye Zhizhen

Structural Characterization and Photoluminescent Properties of Zn1-xMgxO Films on Silicon

Zn1-xMgxO films have been grown on silicon at various substrate temperatures by pulsed laser deposition. The structural and photoluminescent properties of films as a function of substrate temperature have been studied. The optimized substrate temperature is 650°C. The x-ray diffraction spectra indicate that the films are highly C-axis oriented, and no phase separation is observed. The crystal grain size of the films is about 100 nm as examined by atomic force microscopy. The cross-sectional transmission electron microscopy verified the C-axis orientation of the Zn1-xMgxO. These films showed ultraviolet photoluminescence at room temperature. The near-band-edge emission peak of the Zn1-xMgxO film deposited at 600°C has a blueshift (0.40 eV) larger than that of the film deposited at 500°C (0.33 eV). The ratio of the near-band-edge to defect level peak intensity is as large as 159.

Characterizations of Tb:Zn2SiO4 films on silicon wafer prepared by sol-gel dip-coating and solid-phase reaction

Terbium-doped Zn2SiO4 films were successfully prepared on Si wafers by a simple sol-gel dip-coating and solid-phase reaction method of ZnO and SiO2. X-ray diffraction (XRD) and UV?Vis absorption results revealed that films processed below 850 degrees C were ZnO in wurzite structure and films processed above 850 degrees C were Zn2SiO4 in wellimite structure. Photoluminescence measurements of the Tb-doped Zn2SiO4 films showed two strong emission bands at 490 and 545nm. The photoluminescence lifetime was 4.6ms.

Structural, optical and electrical properties of ZnO thin films prepared by reactive deposition

Abstract Highly c -axis oriented crystalline ZnO thin films were prepared on glass substrates by reactive deposition using zinc acetate as the zinc source. The structural, optical, and electrical properties of the ZnO samples were investigated using XRD, UV–Vis absorption and Hall-effect measurements. The dependences of the film properties on the substrate temperature and the source temperature were studied, and the optimal parameters were obtained. Factors that affect the carrier mobility were also analyzed.

Room-temperature electroluminescence of p-ZnxMg1 xO:Na/n-ZnO p-n junction light emitting diode

p-ZnxMg1−xO:Na/n-ZnO p–n junction light emitting diode (LED) was produced on n-ZnO (0001) single-crystal substrate using pulsed laser deposition. The realization of band gap engineering was achieved by the incorporation of Mg in ZnO layers and was confirmed by photoluminescence spectrum. The p-type ZnxMg1−xO:Na film with low resistance was obtained at 500 °C and in which, Na has taken effect evidenced by Hall and X-ray photo-electron spectroscopy measurements. The current-voltage curve of LED showed a rectifying behavior and obvious electroluminescence was realized by feeding a direct current up to 40 mA. Furthermore, its structural and electric characters are discussed as well.

GaN-based quantum dots

Abstract During the last few years efficient light emitting devices have been developed from UV to IR in the III-N system, opening up a very large application field. The problem with the present III-N emitters is the high defect (dislocation) density in the material produced to date. One approach to eliminate the influence of dislocations on light emitting structures is to use zero-dimensional quantum dot (QD) structures in the active part of the material. In this article, we will review the growth mode, methods and the types of III-N QDs achieved in the last few years and the applications of QDs in devices will be introduced finally.

Transparent Conductive Al-Doped ZnO/Cu Bilayer Films Grown on Polymer Substrates at Room Temperature

Al-doped ZnO (AZO)/Cu bi-layer films are deposited by dc magnetron sputtering on polycarbonate substrates at room temperature. The structural, electrical and optical properties of the films are investigated at various sputtering powers of the Cu layer. The AZO/Cu bi-layer film deposited at a moderate sputtering power of 180 W for the Cu layer displayed the highest figure of merit of 3.47 × 10−3Ω−1, with a low sheet resistance of 12.38 Ω/sq, an acceptable visible transmittance of 73%, and a high near-infrared reflectance of about 50%.

Evaluation of GaN growth improvement techniques

Recently good quality epilayers of GaN have been grown heteroepitaxially on different substrates using various growth techniques. Buffer layers, epitaxial lateral overgrowth and pendeo-epitaxial overgrowth are the most important and effective techniques that made a revolution in the improvement of the quality and properties of the GaN materials, led to obtain single crystalline GaN films with a smooth surface and reasonable electrical and optical properties. The aim of this paper is to review the different techniques used to improve the quality and properties of the GaN materials, which opened the way for GaN and its alloys to be used in a countless number of applications.

Identification of Acceptor States in Li–N Dual-Doped p-Type ZnO Thin Films

Li–N dual-doped p-type ZnO (ZnO:(Li,N)) thin films are prepared by pulsed laser deposition. The optical properties are studied using temperature-dependent photoluminescence. The LiZn–NO complex acceptor with an energy level of 138 meV is identified from the free-to-neutral-acceptor (e, A0) emission. The Haynes factor is about 0.087 for the LiZn–NO complex acceptor, with the acceptor bound-exciton binding energy of 12meV. Another deeper acceptor state located at 248meV, also identified from the (e, A0) emission, is attributed to zinc vacancy acceptor. The two acceptor states might both contribute to the observed p-type conductivity in ZnO:(Li,N).

Analysis of magnetic mechanisms of 3d-doped ZnO diluted magnetic semiconductors by an abnormal peak on M-T curve

The crystallographic structures and magnetic properties of a Zn0.95Co0.05O thin film deposited on a C-sapphire substrate using a dual-beam pulsed laser deposition method were characterized. It was shown from crystallographic analysis that the film belongs to the wurtzite structure with the C-axis aligned with that of the substrate. Magnetic hysteresis loops were observed till up to room temperature. A small peak around 55 K was noticed on the magnetization vs. temperature curve. The corresponding temperature of the small peak is close to that of ‘the abnormal peak’ reported by X.M. Zhang et al. From the results obtained, no correlation was found between the abnormal peak and the quantum effects. The magnetic behaviors in the Zn0.95Co0.05O film cannot be explained by the ferromagnetism in diluted magnetic semiconductors. The magnetic mechanisms in ZnO-based diluted magnetic semiconductors are also discussed.

Epitaxial Growth of High-Quality Silicon Films on Double-Layer Porous Silicon

The epitaxial growth of a high-quality silicon layer on double-layer porous silicon by ultra-high vacuum/chemical vapour deposition has been reported. The two-step anodization process results in a double-layer porous silicon structure with a different porosity. This double-layer porous silicon structure and an extended low-temperature annealing in a vacuum system was found to be helpful in subsequent silicon epitaxial growth. X-ray diffraction, cross-sectional transmission electron microscopy and spreading resistance testing were used in this work to study the properties of epitaxial silicon layers grown on the double-layer porous silicon. The results show that the epitaxial silicon layer is of good crystallinity and the same orientation with the silicon substrate and the porous silicon layer.