Synthesis and characterization of well-aligned Zn1-xMgxO nanorods and film by metal organic chemical vapor deposition

Well-aligned Zn1-xMgxO nanorods and film with Mg-content x from 0 to 0.051 have been successfully synthesized by metal organic chemical vapor deposition (MOCVD) without any catalysts. The characterization results showed that the diameters and lengths of the nanorods were in the range of 20-80 nm and 330-360 nm, which possessed wurtzite structure with a c-axis growth direction. As the increase of Mg precursor flows into the growth chamber, the morphology of Zn1-xMgxO evolves from nanorods to a film with scale-like surface and the height of the nanorods and the film was almost identical, it is suggested that the growth rate along the c-axis was hardly changed while the growth of six equivalent facets of the type {1 0 (1) over bar 0} of the Zn1-xMgxO has been improved. Photoluminescence and Raman spectra show that the products have a good crystal quality with few oxygen vacancies. With the Mg incorporation, multiple-phonon scattering become weak and broad, and the intensities of all observed vibrational modes decrease. And the ultraviolet near-band-edge emission shows a clear blueshift (x=0.051, as much as 90 meV) and slightly broadening compared with that of pure ZnO nanorods. (C) 2008 Elsevier B.V. All rights reserved.

Phase-separation suppression in GaN-rich side of GaNP alloys grown by metal-organic chemical vapor deposition

The GaN-rich side of GaNP ternary alloys has been successfully synthesized by light-radiation heating and low-pressure metal-organic chemical vapor deposition. X-ray diffraction (XRD) rocking curves show that the ( 0002) peak of GaNP shifts to a smaller angle with increasing P content. From the GaNP photoluminescence (PL) spectra, the red shifts from the band-edge emission of GaN are determined to be 73, 78 and 100 meV, respectively, in the GaNP alloys with the P contents of 1.5%, 5.5% and 7.5%. No PL peak or XRD peak related to GaP is observed, indicating that phase separation induced by the short-range distribution of GaP-rich regions in the GaNP layer has been effectively suppressed. The phase-separation suppression in the GaNP layer is associated with the high growth rate and the quick cooling rate under the given growth conditions, which can efficiently restrain the accumulation of P atoms in the GaNP layer.

Optical properties of phase-separated GaN1-xPx alloys grown by light-radiation heating metal-organic chemical vapour deposition

Based on the results of the temperature-dependent photoluminescence (PL) measurements, the broad PL emission in the phase-separated GaNP alloys with P compositions of 0.03, 0.07, and 0.15 has investigated. The broad PL peaks at 2.18, 2.12 and 1.83 eV are assigned to be an emission from the optical transitions from several trap levels, possibly the iso-electronic trap levels related to nitrogen. With the increasing P composition (from 0.03 to 0.15), these iso-electronic trap levels are shown to become resonant with the conduction band of the alloy and thus optically inactive, leading to the apparent red shift (80-160meV) of the PL peak energy and the trend of the red shift is strengthened. No PL emission peak is observed from the GaN-rich GaNP region, suggesting that the photogenerated carriers in the GaN-rich GaNP region may recombine with each other via non-radiation transitions.

Stress reduction in GaN films on (111) silicon-on-insulator substrate grown by metal-organic chemical vapor deposition

The GaN film was grown on the (111) silicon-on-insulator (SOI) substrate by metal-organic chemical vapor deposition and then annealed in the deposition chamber. A multiple beam optical stress sensor was used for the in-situ stress measurement, and X-ray diffraction (XRD) and Raman spectroscopy were used for the characterization of GaN film. Comparing the characterization results of the GaN films on the bulk silicon and SOI substrates, we can see that the Raman spectra show the 3.0 cm(-1) frequency shift of E-2(TO), and the full width at half maximum of XRD rocking curves for GaN (0002) decrease from 954 arc see to 472 are sec. The results show that the SOI substrates can reduce the tensile stress in the GaN film and improve the crystalline quality. The annealing process is helpful for the stress reduction of the GaN film. The SOI substrate with the thin top silicon film is more effective than the thick top silicon film SOI substrate for the stress reduction. (C) 2007 Elsevier B.V. All rights reserved.

Stress evolution influenced by oxide charges on GaN metal-organic chemical vapor deposition on silicon-on-insulator substrate

GaN epilayers have been deposited on silicon-on-insulator (SOI) and bulk silicon substrates. The stress transition thickness and the initial compressive stress of a GaN epilayer on the SOI substrate are larger than those on the bulk silicon substrate, as shown in in situ stress measurement results. It is mainly due to the difference of the three-dimensional island density and the threading dislocation density in the GaN layer. It can increase the compressive stress in the initial stage of growth of the GaN layer, and helps to offset the tensile stress generated by the lattice mismatch.

Fabrication of ZnO and its enhancement of charge injection and transport in hybrid organic/inorganic light emitting devices

ZnO nanocrystals were synthesized by hydrolysis in methanol. X-ray diffraction and photoluminescence spectra confirm that good crystallized ZnO nanoparticles were formed. Utilizing those ZnO nanoparticles and poly [2- methoxy-5 - (3',7'-dimethyloctyloxy)- 1,4-phenylenevinylene] (MDMO-PPV), light emitting devices with indium tin oxide (ITO)/poly(3,4-oxyethyleneoxy-thiophene):poly(styrene sulfonate) (PEDOT:PSS)/ ZnO:MDMO-PPV/Al and ITO/PEDOT:PSS/MDMO-PPV/Al structures were fabricated. Electrolummescence (EL) spectra reveal that EL yield of hybrid MDMO-PPV and ZnO nanocrystals devices increased greatly as compared with pristine MDMO-PPV devices. The current-voltage characteristics indicate that addition of ZnO nanocrystals can facilitate electrical injection and charge transport. The decreased energy barrier to electron injection is responsible for the increased efficiency of electron injection. (c) 2007 Elsevier B.V. All rights reserved.

Improved performance in organic light emitting diodes with a mixed electron donor-acceptor film involved in hole injection

Organic light emitting diodes using a mixed layer of electron acceptor 3, 4, 9, 10 perylenetetracarboxylic dianhydride and electron donor copper phthalocyanine (PTCDA:CuPc) on indium tin oxide (ITO) anodes were fabricated. The device properties were found to be strongly dependent on the thickness of the PTCDA:CuPc film: both the power efficiency and the driving voltage of the device were optimized with a thickness of PTCDA:CuPc ranging from 10 to 20 nm. As compared to the conventional ITO/CuPc hole injection structure, the ITO/PTCDA:CuPc hole injection structure could remarkably enhance both the luminance and the power efficiencies of devices. A mechanism of static-induced, very efficient hole-electron pairs generation in mixed PTCDA:CuPc films was proposed to explain the experimental phenomena. The structural and optical properties of PTCDA:CuPc film were examined as well. (c) 2007 American Institute of Physics.

Al compositional inhomogeneity of AlGaN epilayer with a high Al composition grown by metal-organic chemical vapour deposition

The A1 compositional distribution of A1GaN is investigated by cathodoluminescence (CL). Monochromatic CL images and CL spectra reveal a lateral A1 compositional inhomogeneity, which corresponds to surface hexagonal patterns. Cross-sectional CL images show a relatively uniform Al compositional distribution in the growth direction, indicating columnar growth mode of A1GaN films. In addition, a thin A1GaN layer with lower Al composition is grown on top of the buffer A1N layer near the bottom of the A1GaN epilayer because of the larger lateral mobility of Ga adatoms on the growth surface and their accumulation at the grain boundaries.

Organic light emitting diodes with an organic acceptor/donor interface involved in hole injection

Organic light emitting diodes with an interface of organic acceptor 3-, 4-, 9-, 10-perylenetetracarboxylic dianhydride (PTCDA) and donor copper phthalocyanine (CuPc) involved in hole injection are fabricated. As compared to the conventional device using a 5 nm CuPc hole injection layer, the device using an interface of 10 nm PTCDA and 5 rim CuPc layers shows much lower operating voltage with an increase of about 46% in the maximum power efficiency. The enhanced device performance is attributed to the efficient hole generation at the PTCDA/CuPc interface. This study provides a new way of designing hole injection.

Growth of single crystalline ZnxCd1-xS nanocombs by metallo-organic chemical vapor deposition

Single crystalline ternary ZnxCd1-xS nanocombs, which have 'comb' shaped' teeth on one side, have been synthesized by a one-step metallo-organic chemical vapor deposition process at a low temperature of 420 degrees C. The asymmetric, growth behavior of the nanocombs is likely to be induced by the polarization of the c-ptane. Because of the uniform structure and perfect geometrical shape, the nanoteeth could be potentially useful as nanocantilever arrays for nanosensors and, nanotweezers. (c) 2006 Elsevier B.V. All rights reserved.

Effects of grain size on the mosaic tilt and twist in InN films grown on GaN by metal-organic chemical vapor deposition

The structural property of InN films grown on Ga-face GaN layers by metal-organic chemical vapor deposition has been studied by high-resolution x-ray diffraction. The mosaic tilt and twist are found to be strongly dependent on the surface lateral grain size. The twist decreases with increasing grain size and finally approaches to a constant level. On the other hand, the mosaic tilt increases substantially when the grain size becomes large enough and exceeds the width of step terraces on the GaN surface, showing an important mechanism for the defect generation in the InN/GaN system with large out-of-plane lattice mismatch. (c) 2006 American Institute of Physics.

InN nanoflowers grown by metal organic chemical vapor deposition

Hexangular indium nitride nanoflower pattern is observed from scanning electron microscopy and atomic force microscopy. The sample is grown on c-plane (0001) sapphire by metal organic chemical vapor deposition with intentional introduction of hydrogen gas. With the aid of hydrogen, a stable existence of metallic indium is achieved. This will induce the growth of InN nanoflowers via self-catalysis vapor-liquid-solid (VLS) process. It is found that the VLS process is modulated by the interface kinetics and thermodynamics among the sapphire substrate, indium, and InN, which leads to the special morphology of the authors' InN nanoflower pattern. (c) 2006 American Institute of Physics.

Magnetophotoluminescence of Zn0.88Mn0.12Se grown by metal-organic chemical vapor deposition on GaAs substrates

Magnetophotoluminescence properties of Zn0.88Mn0.12Se thin films grown by metal-organic chemical vapor deposition on GaAs substrates are investigated in fields up to 10 T. The linewidth of the excitonic luminescence peaks decreases with the increasing magnetic field (< 1 T), but the peak energy is almost unchanged. There is a crossover of the photoluminescence intensities between interband and bound excitonic transitions as the magnetic field is increased to about 1 T. These behaviors are interpreted by the strong tuning of the local alloy disorder potential by the applied magnetic field. In addition, the magnetic field-induced suppression of the energy transfers from excitons to Mn2+ ions is also observed.

A passively mode-locked diode-end-pumped Nd : YAG laser with a semiconductor saturable absorber mirror grown by metal organic chemical vapour deposition

We report the experimental results of a mode-locked diode-end-pumped Nd:YAG laser with a semiconductor saturable absorber mirror (SESAM) from which we achieved a 10 ps pulse duration at 150 MHz repetition rate. The SESAM was grown by metal organic chemical vapour deposition at low temperature. The recovery time was measured to be 0.5 ps, indicating the potential pulse compression to sub-picoseconds.

Defects in GaN films grown on Si(111) substrates by metal-organic chemical vapour deposition

We report the transmission-electron microscopy study of the defects in wurtzitic GaN films grown on Si(111) substrates with AIN buffer layers by the metal-organic chemical vapour deposition method. The In0.1Ga0.9N/GaN multiple quantum well (MQW) reduced the dislocation density by obstructing the mixed and screw dislocations passing through the MQW. No evident reduction of the edge dislocations density by the MQW was observed. It was found that dislocations with screw component can be located at the boundaries of sub-grains slightly in-plane misoriented.