Shuren Yang

Control of conductivity type in undoped ZnO thin films grown by metalorganic vapor phase epitaxy

The properties of the ZnO thin films prepared by metalorganic vapor phase epitaxy under various oxygen partial pressures were thoroughly studied. It was found that the conduction type in undoped ZnO epilayers could be controlled by adjusting the family VI precursor, oxygen partial pressure during growth. The films were characteristic of n-type conductivity under oxygen partial pressure lower than 45 Pa. With the increase of oxygen content, the crystallinity of the ZnO thin films was degraded to polycrystalline with additional (10–12) orientation and the intrinsic p-type ZnO was produced as the oxygen partial pressure was larger than 55 Pa. The hole concentration and mobility could reach to 1.59×1016 cm−3 and 9.23 cm2 V−1 s−1, and the resistivity was 42.7 Ω cm. The near-band-edge emission and the deep level emission in photoluminescence (PL) spectra at room temperature were influenced strongly by the oxygen partial pressure. Temperature-dependent PL spectra in n-type ZnO films showed a dominant neutral-don...

Effect of annealing on ZnO thin films grown on (001) silicon substrate by low-pressure metalorganic chemical vapour deposition

ZnO thin films were deposited on (001) Si substrate by low-pressure metalorganic chemical vapour deposition. Thermal annealing was performed at 800 °C in air for an hour. The effects of annealing on the surface morphology, stoichiometric ratio, structural and optical properties of ZnO films were investigated using scanning electron microscopy, x-ray photoemission spectroscopy (XPS), x-ray diffraction, Raman spectra and photoluminescence spectra. The resistivity of ZnO film increased to 1.25 × 102 Ω cm after annealing. It was found that the quality of ZnO film could be improved through annealing.

Synthesis of ultrafine gallium nitride powder by the direct current arc plasma method

Ultrafine gallium nitride (GaN) powder has been synthesized by the dc arc plasma method through the reaction of metal gallium (Ga) with the mixture gas of nitrogen ( N2) and ammonia ( NH3). The analyses of the produced powder by x‐ray diffraction, transmission electron microscopy, and selected‐area electron diffraction showed that the GaN particles in wurtzite structure consisted of nanometer‐sized polycrystals and monocrystals. The conversion of Ga to GaN was determined by the mixture ratio of NH3 and N2 in the mixture gas. The morphology of the GaN particles was mainly hexagonal with the size about 20–200 nm. When heated in air or nitrogen atmosphere, the thermostablity of the GaN powder was different.

Structural and optical properties of ZnO film by plasma-assisted MOCVD

High quality ZnO film was deposited by plasma-assisted metal-organic chemical vapor deposition (MOCVD). We observed a dominant peak at 34.6° due to (0 0 2) ZnO, which indicated that the growth of ZnO film was strongly C-oriented. The full-width at half-maximum (FWHM) of the ω-rocking curve was 0.56° indicating relatively small mosaicity. Photoluminescence (PL) measurement was performed at both room temperature and low temperature. Ultraviolet (UV) emission at 3.30 eV was found with high intensity at room temperature while the deep level transition was weakly observed at 2.513 eV. The ratio of the intensity of UV emission to that of deep level emission was as high as 193, which implied high quality of ZnO film. From PL spectrum at 10 K, we observed A-exciton emission at 3.377 eV and D°X bound exciton transition at 3.370 eV. The donor–acceptor transition and LO phonon replicas were observed at 3.333 and 3.241 eV respectively. Raman scattering was performed in back scattering at room temperature. The E2, A1(LO) and A1(TO) mode was seen at 437.6, 575.8 and 380 cm−1 respectively. In comparison with Raman spectrum of ZnO powder, we found that ZnO film was nearly free of strain, which indicated high crystal quality.

Two-step growth of ZnO thin films on diamond/Si by low-pressure metal-organic chemical vapour deposition

Two-step growth method was used to grow high-quality ZnO thin film on polycrystalline diamond/Si with (001) orientation by low-pressure metal-organic chemical vapour deposition. X-ray diffraction spectra and photoluminescence (PL) spectra clearly showed that the quality of ZnO film was improved by two-step growth method. Strong ultraviolet emission was observed while deep level emission could be hardly observed in room-temperature PL spectrum of ZnO thin film grown by two-step method. Emission from excitons bound to donors was observed in 100 K PL spectrum.

Characteristics of InAs quantum dots on GaAs/InP with different InAs coverage

In this article, a thin tensile GaAs interlayer was used to get narrower size distribution and regular arrangement of InAs quantum dots (QDs) on InP substrate by low-pressure metalorganic chemical vapor deposition. The comparison results of the photoluminescence spectrum and the atomic force microscopy image show better properties after using GaAs interlayer. Also investigated were the surface behaviors of InAs QDs with different InAs coverage on GaAs/InP in order to reveal the detailed information of InAs QDs.

Characterization of InxGa1−xAs/InP epilayers by X-ray double crystal rocking curve peak profile analysis

Abstract Katos statistical theory of X-ray dynamical diffraction was generalized to the case of diffraction by epitaxial layers and was applied to analyze the X-ray double crystal rocking curves of In x Ga 1−x As InP single epilayers in this paper. It is shown that the statistical theory provides us with quantitative information about the perfectness as well as thicknesses and compositions of the epilayer. Moreover, some confusing experimental values can be interpreted by taking into account the effect of diffuse scattering. The statistical theory can help us to obtain much more information which is significant for improving the quality of the epilayer through optimizing the growth conditions.

Effect of thin GaAs tensile-strained layer on InAs quantum dots on InP (001) substrate grown by LP-MOVPE

Abstract The InAs quantum dots on thin tensile-strained GaAs layer on InP (001) substrate are grown by LP-MOVPE. Approximately 2 nm GaAs tensile-strained layer is first grown on InP substrate, then 2 monolayer (ML) InAs for sample A, 4 ML for sample B, 6 ML for sample C and 8 ML for sample D are deposited. An atomic force microscope (AFM) is used to study the behavior of the InAs quantum dots. For sample A, two types of InAs islands are observed. Strain-induced grooves appear on the surface. For the other three samples, the InAs islands arrange along two orthogonal directions and the island density decreases with an increase in the amount of InAs material. The density of sample B is as high as 1.9×10 10 cm −2 , the densities are 1.39×10 10 and 0 .79×10 10 cm −2 for samples C and D, respectively. Furthermore, the base shape changes for different samples. For samples A and B, the base shapes are round; for sample C, the base changes into ellipsis; but for sample D, the base changes into triangle. The base area increases with an increase in the deposition of InAs. We also investigate the PL spectrum of InAs QDs with GaAs and with it and find that the QDs quality is higher with GaAs layer.

Studying the mechanism of ordered growth of InAs quantum dots on GaAs/InP

Abstract We study the mechanism of ordered growth of InAs quantum dots (islands) on a GaAs/InP substrate in theory and point out that the tensile strain can be used to control InAs/InP self-assembled quantum dots arrangement. Photoluminescence spectrum, and atomic force microscopy images have been investigated. In the experiment, ordered InAs islands have been obtained and the maximum density of quantum dots is 1.6×10 10 cm −2 at 4 monolayers InAs layer.

Analysis of room temperature PL spectra of InAs/GaAs/InP and InAs/InP self-assembled QDs: A five-band study

In this paper, room temperature PL spectra of InAs self-assembled dots grown on GaAs/InP and InP substrate are presented. For analyzing different positions of the PL peaks, we examine the strain tensor in these quantum dots (QDs) using a valence force field model, and use a five-band k·p formalism to find the electronic spectra. We find that the GaAs tensile-stained layer affects the position of room temperature PL peak. The redshift of PL peak of InAs/GaAs/InP QDs compared to that of InAs/InP QDs is explained theoretically.