J.W. Liang
Chinese Academy of Sciences
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Featured researches published by J.W. Liang.
Journal of Crystal Growth | 2003
Xinhe Zheng; Y.T. Wang; Zhigang Feng; H. Yang; H. Chen; J.M. Zhou; J.W. Liang
An extended technique derived from triple-axis diffraction setup was proposed to measure lattice parameters of cubic GaN(c-GaN) films. The fully relaxed lattice parameters of c-GaN are determined to be 4.5036+0.0004 Angstrom, which is closer to the values of a hypothetical perfect crystal. The speculated zero setting correction (Deltatheta) is very slight and within the range of the accuracy of measurement. Additionally, we applied this method to analyze strain of four different kinds of c-GaN samples. It is found that in-plane strain caused by large lattice mismatch and thermal expansion coefficients mismatch directly influence the epilayer growth at high temperatures, indicating that the relaxation of tensile strain after thermal annealing helps to improve the crystalline quality of c-GaN films and optical properties
Applied Physics Letters | 2006
D. G. Zhao; Hui Yang; J.J. Zhu; D. S. Jiang; Z. S. Liu; Siriguleng Zhang; Y.T. Wang; J.W. Liang
The effects of dislocations and Si doping on the electrical properties of n-type GaN grown by metal organic chemical vapor deposition (MOCVD) are investigated. It is found that both electron mobility and carrier concentration are strongly influenced by edge dislocations. A moderate Si doping during the GaN growth improves the electron mobility, but the best doping effect depends on the dislocation density of the sample. High quality about 4-μm-thick MOCVD-grown GaN film with a room temperature electron mobility as high as 1005cm2∕Vs is obtained by optimizing growth conditions.
Applied Physics Letters | 2006
Jingli Wang; D. Z. Yao; J. Chen; J.J. Zhu; D. G. Zhao; D. S. Jiang; H. Yang; J.W. Liang
The strain evolution of the GaN layer grown on a high-temperature AlN interlayer with GaN template by metal organic chemical vapor deposition is investigated. It is found that the layer is initially under compressive strain and then gradually relaxes and transforms to under tensile strain with increasing film thickness. The result of the in situ stress analysis is confirmed by x-ray diffraction measurements. Transmission electron microscopy analysis shows that the inclination of edge and mixed threading dislocations rather than the reduction of dislocation density mainly accounts for such a strain evolution. (c) 2006 American Institute of Physics.
Journal of Physics: Condensed Matter | 2007
X.L. Wang; D. G. Zhao; D. S. Jiang; H. Yang; J.W. Liang; U Jahn; K. Ploog
The Al compositional distribution of AlGaN is investigated by cathodoluminescence (CL). Monochromatic CL images and CL spectra reveal a lateral Al 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 AlGaN films. In addition, a thin AlGaN layer with lower Al composition is grown on top of the buffer AlN layer near the bottom of the AlGaN epilayer because of the larger lateral mobility of Ga adatoms on the growth surface and their accumulation at the grain boundaries.
Journal of Physics D | 2002
G Feng; Yingying Fu; J S Xia; J.J. Zhu; Bo Zhang; Xu Shen; D. G. Zhao; H. Yang; J.W. Liang
The lateral epitaxial overgrowth of GaN was carried out by low-pressure metalorganic chemical vapor deposition, and the cross section shape of the stripes was characterized by scanning electron microscopy. Inclined {11–2n} facets (n ≈ 1–2.5) were observed in the initial growth, and they changed gradually into the vertical {11–20} sidewalls in accordance with the process of the lateral overgrowth. A model was proposed utilizing diffusion equations and boundary conditions to simulate the concentration of the Ga species constituent throughout the concentration boundary layer. Solutions to these equations are found using the two-dimensional, finite element method. We suggest that the observed evolution of sidewall facets results from the variation of the local V/III ratio during the process of lateral overgrowth induced by the lateral supply of the Ga species from the SiNx mask regions to the growing GaN regions.
Journal of Applied Physics | 2007
D. G. Zhao; D. S. Jiang; J.J. Zhu; Z. S. Liu; Suyun Zhang; J.W. Liang; H. Yang
It is studied whether there is any regular relationship between the yellow luminescence band and electron mobility of n-type GaN. For a series of GaN samples grown with the same Si doping, it is found that the electron mobility decreases with an increase of relative intensity of yellow luminescence, accompanied by an increase of edge dislocation density. Further research indicates that it is acceptors introduced by edge dislocations which lead to the concomitant changes of yellow luminescence and electron mobility. Similar changes are induced by Si doping in the n-type GaN samples with relatively low edge dislocation density. However, the relationship between the yellow luminescence and electron mobility of n-type GaN is not a simple one. A light Si doping may simultaneously increase yellow luminescence and electron mobility when Si doping plays a dominant role in reducing the carrier scattering. This means that even the intensity of yellow luminescence is often used as an indicator of material quality for GaN, it does not have any monotonous correlation with the electron mobility of GaN. (c) 2007 American Institute of Physics.
Journal of Physics D | 2007
X.L. Wang; D. G. Zhao; Uwe Jahn; K. Ploog; D. S. Jiang; H. Yang; J.W. Liang
We have investigated the growth of AlGaN epilayers on a sapphire substrate by metalorganic chemical vapour deposition using various low-temperature ( LT) AlN buffer thicknesses. Combined scanning electron microscopy and cathodoluminescence investigations reveal the correlation between the surface morphology and optical properties of AlGaN films in a microscopic scale. It is found that the suitable thickness of the LT AlN buffer for high quality AlGaN growth is around 20 nm. The Al compositional inhomogeneity of the AlGaN epilayer is attributed to the low lateral mobility of Al adatoms on the growing surface.
Journal of Crystal Growth | 2002
G. Feng; Xinhe Zheng; Yingying Fu; J.J. Zhu; Xu Shen; B.S. Zhang; D. G. Zhao; Y.T. Wang; H. Yang; J.W. Liang
The crystallographic tilt of the lateral epitaxial overgrown (LEO) GaN on sapphire Substrate with SiNx mask is investiaated by double crystal X-ray diffraction. Two wing peaks beside the GaN 0002 peak can be observed for the as-grown LEO GaN. During the selective etching of SiNx mask, each wing peak splits into two peaks, one of which disappears as the mask is removed, while the other remains unchanged. This indicates that the crystallographic tilt of the overgrown region is caused not only by the plastic deformation resulted from the bending of threading dislocations, but by the non-uniformity elastic deformation related with the GaN, SiNx interfacial forces. The widths of these two peaks are also studied in this paper
Journal of Physics D | 2008
Zuju Ma; D. G. Zhao; Y.T. Wang; D. S. Jiang; Suyun Zhang; J.J. Zhu; Z. S. Liu; B J Sun; Hui Yang; J.W. Liang
The effect of the growth temperature on the surface and interface quality for the GaN/AlN multiquantum well (MQW) layer grown by metal-organic vapour chemical deposition is investigated. The obtained GaN/AlN MQW structure is almost coherent to the underlying AlGaN layer at improved growth conditions. With a relatively low growth temperature, the GaN/AlN MQW growth rate increases, the surface roughness reduces considerably and no macro steps are observed, resulting in a better periodicity of MQW.
Journal of Crystal Growth | 2003
G. Feng; Xu Shen; J.J. Zhu; B.S. Zhang; D. G. Zhao; Y.T. Wang; H. Yang; J.W. Liang
A new method of measuring the thickness of GaN epilayers on sapphire (0 0 0 1) substrates by using double crystal X-ray diffraction was proposed. The ratio of the integrated intensity between the GaN epilayer and the sapphire substrate showed a linear relationship with the GaN epilayer thickness up to 2.12 mum. It is practical and convenient to measure the GaN epilayer thickness using this ratio, and can mostly eliminate the effect of the reabsorption, the extinction and other scattering factors of the GaN epilayers