A geometrical model of GaN morphology in initial growth stage

Based on morphology observed by atomic force microscopy, a geometrical model was proposed in order to explain the statistical results obtained from morphology observation on GaN in initial growth stage. Four parameters were introduced to describe the morphology characteristics in this model. Least-square fitting of height distribution was performed. The height distribution derived from the model agreed well with that obtained from experimental records. It was also found that the model should be further advanced to understand the growth of GaN in initial growth stage. (C) 2002 Elsevier Science BY. All rights reserved.

Influence of ion energy and deposition temperature on the surface morphology of carbon films deposited by ion beams

Carbon films were deposited by mass-selected ion beam technique with ion energies 50-200eV at a substrate temperature from room temperature to 80 degreesC,. For the energies used, smooth diamond-like carbon films were deposited at room temperature. When the substrate temperature was 600 degreesC,rough graphitic films were produced. But highly oriented carbon tubes were observed when the energies were larger than 140eV at 800 degreesC. They were perpendicular to the surface and parallel to each other. preferred orientation of graphite basic plane was observed by high-resolution electron microscopy. Shallow ion implantation and stress are responsible for this orientation.

The effect of substrate orientation on the morphology of InAs nanostructures on (001) and (11n)A/B(n=1-5) InP substrates

Strained InAs nanostructures have been grown by solid-source molecular beam epitaxy in In0.52Al0.48As matrix on different InP substrate surfaces ((0 0 1) and (1 1 n)A/B (n = 1 - 5)). The morphology of the nanostructures was characterized using atomic force microscopy (AFM). The AFM results reveal interesting differences in the size, shape, and alignment of the nanostructures between different oriented surfaces. It was found that some faceted nanostructures tend to form on A-type surfaces, the shape and the alignment of these nanostructures show clear dependence on the substrate orientation. Samples grown on (0 0 1) and B-type surfaces showed preferentially dense round dots. Dots formed on (1 1 3)B, (1 1 3)B and (1 1 5)B surfaces have a higher dot density and size homogeneity, which shows a potential for the production of high-quality and customized self-assembled quantum dots for photonics applications. (C) 2000 Elsevier Science B.V. All rights reserved.

Annealing effect on the surface morphology and photoluminescence of InGaAs/GaAs quantum dots grown by molecular beam epitaxy

Postgrowth rapid thermal annealing was performed on InGaAs/GaAs quantum dots grown by molecular beam epitaxy. The blue shift of the emission peak and the narrowing of the luminescence line width are observed at lower annealing temperature. However, when the annealing temperature is increased to 850 degrees C, the emission line width becomes larger. The TEM image of this sample shows that the surface becomes rough, and some large clusters are formed, which is due to the interdiffusion of In, Ga atoms at the InGaAs/GaAs interface and to the strain relaxation. The material is found to degrade dramatically when the annealing temperature is further increased to 900 degrees C, while emission from quantum dots can still be detected, along with the appearance of the emission from excited state. (C) 2000 Elsevier Science B.V. All rights reserved.

Influence of indium composition on the surface morphology of self-organized InxGa1-xAs quantum dots on GaAs substrates

InxGa1-xAs self-organized quantum dots with x=1.0, 0.5, and 0.35 have been grown by molecular beam epitaxy. The areal density, distribution, and shapes have been found to be dependent on x. The dot shape changes from a round shape for x=1.0 to an elliptical shape for x less than or equal to 0.5. The major axis and minor axis of the elliptical InxGa1-xAs dots are along the [(1) over bar 10] and [110] directions, respectively. The ordering phenomenon is also discussed. It is suggested that the dot-dot interaction may play important roles in the self-organization process. (C) 2000 American Institute of Physics. [S0021-8979(00)10701-7].

Morphology and photoluminescence of GeSi self-assembled quantum dot on Si(113)

Morphology of self-assembled GeSi quantum dot grown on Si(113) by Si molecular beam epitaxy has been studied by transmission electron microscopy and atomic force microscopy. Photoluminescence from the as-grown sample and annealed sample was studied. The results were analyzed and explained.

Morphology and wetting layer properties of InAs/GaAs nanostructures

In this work, we present the growth of InAs rings by droplet epitaxy. A complete process from the rings formation to their density saturation has been demonstrated: A morphological evolution with the varying of the indium deposition amount has been, clearly observed. Our results indicate that there, is a critical deposition amount (similar to 1.1 ML) for the indium to form InAs dots before droplets form; there is also a critical deposition amount (similar to 1.4 ML) to form InAs ring, but it is caused by the formation of droplets as the deposition amount increases. The density of the rings saturates when the deposition amount exceeds similar to 3.3 ML; because the adsorbed indium atoms block sites for further adsorption and the following supplied In only contributes to the size increase of In droplets. Still, as the In deposition amount increases, we can find coupled quantum rings. Moreover, the wetting layer properties of these structures are studied by reflectance difference spectroscopy, which shows a complicated evolution with the In amount. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Surface morphology evolution of strained InAs/GaAs(331)a films

Surface morphology evolution of strained InAs/GaAs(331)A films was systematically investigated in this paper. Under As-rich conditions, InAs elongated islands aligned along [1 (1) over bar0] are formed at a substrate temperature of 510 degrees C. We explained it as a result of the anisotropic diffusion of adatoms. Under In-rich conditions, striking change has occurred with respect to the surface morphology of the InAs layers. Instead of anisotropic InAs elongated islands, unique island-pit pairs randomly distributed on the whole surface were observed. Using cooperative nucleation mechanisms proposed by Jesson et al. [Phys. Rev. Lett. 77, 1330 (1996)], we interpret the resulting surface morphology evolution.

Synthesis of GaN nanorods with vertebra-like morphology

GaN nanorods with vertebra-like morphology were synthesized by nitriding Ga2O3/ZnO films at 1000 degrees C for 20min. Ga2O3 thin films and ZnO middle layers were pre-deposited in turn on Si(111) substrates by r.f. magnetron sputtering system. In the flowing ammonia ambient, ZnO was reducted to Zn and Zu sublimated at 1000 degrees C. Ga2O3 was reducted to Ga2O and Ga2O reacted with NH3 to synthesize GaN nanorods in the help of the sublimation of Zn. The structure and morphology of the nanorods were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), The composition of GaN nanorods was studied by energy dispersive spectroscopy (EDS) and fourier transform infrared (FTIR) system.

Study on surface morphology of GaN growth by MOCVD on GaN/Si(111) template

The surface morphology of GaN grown by MOCVD on GaN/Si template was studied. Rough morphology and deep pinhole defects on some surface areas of the samples were observed and studied. The formation of rough morphology is possibly related to Ga-Si alloy produced due to poor thermal stability of template at high temperature. The deep pinhole defects generated are deep down to the surface of MBE-grown GaN/Si template. The stress originated from the large thermal expansion coefficient difference between GaN and Si may be related to the formation of the pinhole defects. The surface morphology of the GaN can be improved by optimizing the GaN/Si template and decreasing the growth temperature.

A kinetic model for nanocrystal morphology evolution

A kinetic model is developed with the goal of understanding and predicting the morphology evolution of nonocrystals in nonequilibrium growth conditions. The model is based on the assumption that under such conditions, different crystal planes have different kinetic parameters. This model focuses on the morphology-developing stage and is successfully related to the nucleation process and other crystal evolution mechanisms. It is believed to be a universal model and is applied to discuss the morphology evolution of CdSe nanocrystals, including the aspect ratio, injection I schemes, ligands effect and morphology distribution.

Structural ordering and interface morphology in symmetrically strained (GaIn)As/Ga(PAs) superlattices grown on off-oriented GaAs(100)

In this work we investigate the structural properties of symmetrically strained (GaIn)As/GaAs/Ga(PAs)/GaAs superlattices by means of x-ray diffraction, reciprocal-space mapping, and x-ray reflectivity. The multilayers were grown by metalorganic vapor-phase epitaxy on (001) GaAs substrates intentionally off-oriented towards one of the nearest [110] directions. High-resolution triple-crystal reciprocal-space maps recorded for different azimuth angles in the vicinity of the (004) Bragg diffraction clearly show a double periodicity of the x-ray peak intensity that can be ascribed to a lateral and a vertical periodicity occurring parallel and perpendicular to the growth surface. Moreover, from the intensity modulation of the satellite peaks, a lateral-strain gradient within the epilayer unit cell is found, varying from a tensile to a compressive strain. Thus, the substrate off-orientation promotes a lateral modulation of the layer thickness (ordered interface roughness) and of the lattice strain, giving rise to laterally ordered macrosteps. In this respect, contour maps of the specular reflected beam in the vicinity of the (000) reciprocal lattice point were recorded in order to inspect the vertical and lateral interface roughness correlation, A semiquantitative analysis of our results shows that the interface morphology and roughness is greatly influenced by the off-orientation angle and the lateral strain distribution. Two mean spatial wavelengths can be determined, one corresponding exactly to the macrostep periodicity and the other indicating a further interface waviness along the macrosteps. The same spatial periodicities were found on the surface by atomic-force-microscopy images confirming the x-ray results and revealing a strong vertical correlation of the interfaces up to the outer surface.