Microstructure of GaN Grown on (1120) Sapphire

ABSTRACTMost of the work done on GaN has taken into account layers grown on the (0001) sapphire. However one would expect the growth on (1120) to lead to different structural defects. As has been shown, in one direction, the mismatch is rather small. In this work, we have carried out structural analysis of layers and interfacial relationship. Inside the layers, the density of defects is comparable to that found conventionally in layers grown on top of (0001) sapphire. The growth mode is also mosaic with a grain size of a few microns. One interesting result is the interface structure, which differs from conventional growth where a flat or stepped interface is formed with a large distance between steps. In this case, the interface is found to be rough at the atomic scale so that this roughness has a random distribution. Moreover, the misfit dislocation spacing is 1nm which is only half the dislocation spacing found in GaN growth on (0001) sapphire.

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Effect of growth temperature on the microstructure of the nucleation layers of GaN grown by MOCVD on (1120) sapphire

MRS Proceedings ◽

10.1557/proc-743-l3.19 ◽

2002 ◽

Vol 743 ◽

Author(s):

T. Wojtowicz ◽

P. Ruterana ◽

M. E. Twigg ◽

R. L. Henry ◽

D. D. Koleske ◽

...

Keyword(s):

High Temperature ◽

Structural Analysis ◽

Growth Temperature ◽

Structural Parameters ◽

Three Dimensional ◽

Nucleation Mechanism ◽

Structural Defects ◽

Orientation Relationships ◽

Island Growth ◽

Work Done

AbstractMost of the work done on GaN has taken into account layers grown on the (0001) sapphire plane. However one would expect the growth on the (1120) plane to lead to different structural defects. As has been shown, in one direction, the mismatch is rather small. In this work, we have carried out structural analysis of nucleation layers grown at temperatures ranging from 600°C to 1100°C. It is shown that for many of the structural parameters, such as the orientation relationships, the layer morphology and the nucleation mechanism critically depend on the growth temperature. At the lowest temperatures, the growth is completely three dimensional with a mixture of the two traditional orientation relationships, but the coalescence thickness is small. In a next step, the A orientation relationship predominates and the layer roughness tends to slightly decrease. This orientation is never perfect, and there is always 1.5° misorientation to the same direction in sapphire, whereas the B orientation is always perfect. At an intermediate temperature, island growth is predominant, whereas towards the high temperature end the B orientation becomes predominant. For the highest growth temperatures, the nucleated layers are completely flat and with the B orientation, although they contain a quite large number of defects such as inversion domains.

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Atomic-scale analysis of the interface structure and lattice mismatch relaxation of Bi2Sr2CaCu2O8+δ/SrTiO3 heterostructure

Ceramics International ◽

10.1016/j.ceramint.2020.11.233 ◽

2020 ◽

Author(s):

Jian Zhang ◽

Weizhen Wang ◽

Tianlin Wang ◽

Lili Jiang ◽

Nan Wang ◽

...

Keyword(s):

Lattice Mismatch ◽

Interface Structure ◽

Atomic Scale ◽

Scale Analysis

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Structural Analysis at an Atomic Scale Using Spherical Aberration Corrected Electron Microscope

Nihon Kessho Gakkaishi ◽

10.5940/jcrsj.54.159 ◽

2012 ◽

Vol 54 (3) ◽

pp. 159-165

Author(s):

Yoshifumi OSHIMA ◽

Yasumasa TANISHIRO ◽

Takayuki TANAKA ◽

Kunio TAKAYANAGI

Keyword(s):

Electron Microscope ◽

Structural Analysis ◽

Spherical Aberration ◽

Atomic Scale ◽

Aberration Corrected

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How To Visualize the Atomic-scale World of Interface Structure and Chemistry

Journal of the Society of Mechanical Engineers ◽

10.1299/jsmemag.101.961_894 ◽

1998 ◽

Vol 101 (961) ◽

pp. 894-896

Author(s):

Sadahiro Tsurekawa

Keyword(s):

Interface Structure ◽

Atomic Scale

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Mechanical Behaviour of Nanocrystalline Copper Related to Grain-boundary Structure

MRS Proceedings ◽

10.1557/proc-727-r3.2 ◽

2002 ◽

Vol 727 ◽

Cited By ~ 2

Author(s):

Y. Champion ◽

P. Langlois ◽

S. Guérin-Mailly ◽

C. Langlois ◽

M. J. Hÿtch

Keyword(s):

Plastic Deformation ◽

Grain Size ◽

Structural Analysis ◽

Grain Boundary ◽

Grain Boundaries ◽

Mechanical Behaviour ◽

Tensile Testing ◽

Metallic Nanostructures ◽

Nanocrystalline Powders ◽

Clear Understanding

AbstractUnderstanding the mechanical behaviour of metallic nanostructures is a key issue for their development. On the one hand, knowledge of the plastic behaviour at various temperatures is essential to control the synthesis, forming, and machining of such materials. Equally, a clear understanding of atomic and mesoscopic mechanisms, involving defects and their interactions, is essential for the control of ageing and functional properties. Regarding plastic deformation at room temperature, there is now evidence for unusual behaviour in nanostructured metals. In addition to high resistance and ductility, tensile testing reveals peculiar elasto-plastic deformation. Such behaviour was initially attributed to grain-boundary sliding. However, intergranular areas (including triple junctions) may possess special properties compared to their microcrystalline counterparts. For example, low activation energies have been measured for grain-boundary diffusion and it has been observed that grain-boundaries may act as dislocation sources and nucleation sites for deformation twinning.In this paper, we report on analysis on bulk copper nanostructures. Grain-boundaries are studied, by cross-correlating information from mechanical tensile testing and structural analysis, including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Macroscopic bulk specimens (with grain size of about 80 nm) are prepared by powder metallurgy techniques, modified to fit to the special properties of nanocrystalline powders. Processing includes coldisostatic pressing, sintering and differential extrusion. The powders used (grain size of 40 nm) are synthesised by evaporation and cryo-condensation of a metallic vapour within liquid nitrogen. Results on mechanical testing and structural analysis will be reported. Emphasis will be placed on the structure of grain-boundaries (type of grain-boundary, grain-boundary thickness) studied by TEM and high resolution TEM image analysed using the geometric phase technique. The nanostructure was revealed to be consist in agglomerate of nano-size grains separated by low angle grain-boundaries. Agglomerates are themselves separerated by general high angle boundaries. These observations will then be related to the unusual mechanical true stress-true strain curves of the metallic nanostructures.

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