Using different carrier gases to control AlN film stress and the effect on morphology, structural properties and optical properties

On the metalorganic chemical vapour deposition growth of AlN, by adjusting H-2+N-2 mixture gas components, we can gradually control island dimension. During the Volmer - Weber growth, the 2-dimensional coalescence of the islands induces an intrinsic tensile stress. Then, this process can control the in-plane stress: with the N-2 content increasing from 0 to 3 slm, the in-plane stress gradually changes from 1.5 GPa tensile stress to - 1.2GPa compressive stress. Especially, with the 0.5 slm N-2 + 2.5 slm H-2 mixture gas, the in-plane stress is only 0.1 GPa, which is close to the complete relaxation state. Under this condition, this sample has good crystal and optical qualities.

Effect of Nitridation on Morphology, Structural Properties and Stress of AIN Films

We investigate effects of nitridation on AIN morphology, structural properties and stress. It is found that 3 min nitridation can prominently improve AIN crystal structure, and slightly smooth the surface morphology. However, 10 min nitridation degrades out-of-plane crystal structure and surface morphology instead. Additionally, 3-min nitridation introduces more tensile stress (1.5 GPa) in AIN films, which can be attributed to the weaker islands 2D coalescent. Nitridation for 10 min can introduce more defects, or even forms polycrystallinity interlayer, which relaxes the stress. Thus, the stress in AIN with 10 min nitridation decreases to -0.2 GPa compressive stress.

The effect of single AlGaN interlayer on the structural properties of GaN epilayers grown on Si (111) substrates

High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single AlGaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si (111) substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlGaN interlayer on the structural proper-ties of the resulting GaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AlGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.

Correlation between optical and structural properties of (Al,Ga)N layers grown by MOCVD

For both, (Al,Ga)N with low Al content grown on a GaN nucleation layer and (AI,Ga)N with high Al content gown on an AlN nucleation layer, the inhomogeneous distribution of the luminescence is linked to the distribution of defects, which may be due to inversion domains. In the former system, defect regions exhibit a much lower Al content than the nominal one leading to a splitting of the respective luminescence spectra. In the latter system, a domain-like growth is observed with a pyramidal surface morphology and non-radiative recombination within the domain boundaries. (c) 2007 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.

Structural properties of polycrystalline silicon films formed by pulsed rapid thermal processing

A novel pulsed rapid thermal processing (PRTP) method has been used for realizing solid-phese crystallization of amorphous silicon films prepared by plasma-enhanced chemical vapour deposit ion. The microstructure and surface morphology of the crystallized films were investigated using x-ray diffraction and atomic Force microscopy. The results indicate that PRTP is a suitable post-crystallization technique for fabricating large-area polycrystalline silicon films with good structural quality, such as large grain size, small lattice microstrain and smooth surface morphology on low-cost glass substrates.

Growth and structural properties of GaN films on flat and vicinal SiC(0001) substrates

Initial stage GaN growth by molecular-beam epitaxy (MBE) on SiC(0001) substrate is followed by in situ scanning tunneling microscopy. Comparison is made between growth on nominally flat and vicinal substrate surfaces and the results reveal characteristic differences between the two. Ex situ transmission electron microscopy (TEM) and X-ray diffraction (XRD) rocking curve measurements of the films show lower density of defects and better structural quality of the vicinal film. We suggest the improved structural quality of the vicinal film is related to the characteristic difference in its initial stage nucleation and coalescence proccsses than that of the flat film.

Structural properties of SI-GaAs grown in space

The structural properties of Semi-insulating gallium arsenide (SI-GaAs) crystal grown with power-travelling technique in space have been studied by double-crystal x-ray diffractometry and chemical etching. The quality of the crystal was first evaluated by x-ray rocking-curve method. The full width at half maximum of x-ray rocking curve in space-grown SI-GaAs is 9.4+/-0.08 are seconds. The average density of dislocations revealed by molten KOH is 2.0 X 10(4) cm(-2), and the highest density is 3.1 X 10(4) cm(-2). The stoichiometry in the single crystal grown in space is improved as well. Unfortunately, the rear of the ingot grown in space is polycrystalline owing to being out of control of power. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

Comparative study of the structural properties of nanocrystalline Ge : H plasma deposited onto the cathode and the anode using high hydrogen dilutions

Nanocrystalline Ge:H thin films were deposited simultaneously on both electrodes of a conventional capacitively coupled reactor for plasma enhanced chemical vapor deposition using highly H-2 diluted GeH4 as the source gas. The structure of the films was investigated by Raman scattering and X-ray diffraction as a function of substrate temperature, H-2 dilution, and r.f. power. The hydrogen concentrations and bonding configurations were determined by infrared absorption spectroscopy. For anodic deposition, the preferred crystallographic orientation and film crystallinity depend rather strongly on the deposition parameters. This dependence can be explained by changing surface mobilities of adsorbed precursors due to changes in the hydrogen coverage of the growing surface. Cathodic deposition is much less sensitive to variations in the deposition parameters. It generally results in films of high crystallinity with randomly oriented crystallizes. Some possible mechanisms for these differences between anodic and cathodic deposition are discussed. (C) 1999 Elsevier Science S.A. All rights reserved.

Influence of Al content on electrical and structural properties of Si-doped AlxGa1-xN/GaN HEMT structures

Improved electrical properties of AlxGa1-xN/GaN high electron mobility transistor (HEMT) structures grown by metalorganic chemical vapor deposition (MOCVD) were achieved through increasing the Al mole fraction in the AlGaN barrier layers. An average sheet resistance of 326.6 Omega/sq and a good resistance uniformity of 98% were obtained for a 2-inch Al0.38Ga0 62N/GaN HEMT structure. The surface morphology of AlxGa1-xN/GaN HEMT structures strongly correlates with the Al content. More defects were formed with increasing Al content due to the increase of tensile strain, which limits further reduction of the sheet resistance. (c) 2006 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim.

Optical and structural properties of ZnO films grown on Si(100) substrates by MOCVD - art. no. 60290G

High quality ZnO films have been successfully grown on Si(100) substrates by Metal-organic chemical vapor deposition (MOCVD) technique. The optimization of growth conditions (II-VI ratio, growth temperature, etc) and the effects of film thickness and thermal treatment on ZnO films' crystal quality, surface morphology and optical properties were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence (PL) spectrum, respectively. The XRD patterns of the films grown at the optimized temperature (300 degrees C) show only a sharp peak at about 34.4 degrees corresponding to the (0002) peak of hexagonal ZnO, and the FWHM was lower than 0.4 degrees. We find that under the optimized growth conditions, the increase of the ZnO films' thickness cannot improve their structural and optical properties. We suggest that if the film's thickness exceeds an optimum value, the crystal quality will be degraded due to the large differences of lattice constant and thermal expansion coefficient between Si and ZnO. In PL analysis, samples all displayed only ultraviolet emission peaks and no observable deep-level emission, which indicated high-quality ZnO films obtained. Thermal treatments were performed in oxygen and nitrogen atmosphere, respectively. Through the analysis of PL spectra, we found that ZnO films annealing in oxygen have the strongest intensity and the low FWHM of 10.44 nm(106 meV) which is smaller than other reported values on ZnO films grown by MOCVD.

Optical and structural properties of self-assembled ZnO QD chains by L-MBE

ZnO complex 3D nano-structures have been self-organized on Al2O3 (0 0 0 1) substrate by laser molecular beam epitaxy (L-MBE). It is shown by AFM morphology that the structure is composed of ID quantum dot chains (QDCs) and larger nano-islands at the nodes of QDCs. The formation mechanism of the nano-structure is also investigated. XRD results indicate that the nano-structure is highly c-axis oriented, with the aligned in-plane oriented domains. Time-integrated photoluminescence (TIPL) of the sample shows obvious blue-shift and broadening of the near band-edge (NBE) emission at room temperature, which are related to the quantum confinement effects. Time-resolved PL (TRPL) result shows bi-exponential decay behavior of ZnO QDCs, with a fast decay time of 38.21 ps and a low decay time of 138.19ps, respectively, which is considered to be originated from the interdot coupling made by coherent emission and reabsorption of the photons in QDCs. (C) 2007 Elsevier B.V. All rights reserved.

Optical and structural properties of anodized AlxGa1-xAs layers

The optical and structural properties of anodized AlxGa1-xAs films were investigated by using optical reflectance, X-ray photoemission and Auger electron spectroscopy (XPS and AES). II was found that the anodization process occurs progressively from the surface to the bulk of AlxGa1-xAs and the formed oxidation film comprises mainly oxides of Al and Ga together with a relatively small amount of As. The refractive indexes of the anodized Al0.8Ga0.2As film and Al0.8Ga0.2As film itself were deduced to be about 1.80 and 3.25, respectively, indicating that the anodization film is desirable for anti-reflection coating of the surface of AlxGa1-xAs/GaAs solar cells. (C) 1997 Elsevier Science S.A.

Assessment of the structural properties of GaAs/Si epilayers using X-ray (004) and (220) reflections

We improved the method previously used to determine the lattice constants and misorientation of GaAs/Si by recording the patterns of X-ray (004) and (220) reflections. The (220) reflection was measured from the (110) cross section of a GaAs/Si epilayer. The structural properties of the GaAs/Si epilayers grown by metal-organic chemical-vapor deposition (MOCVD) using an ultrathin a-Si buffer layer were investigated. The rotation angle of GaAs/Si epilayers grown by MOCVD using an a-Si buffer layer is very small and the lattice constants of these GaAs/Si epilayers agree quite well with elastic theory.

OPTICAL AND STRUCTURAL-PROPERTIES OF AP-MOVPE GAINP/GAAS HETEROSTRUCTURES

Lattice matched GaInP/GaAs heterostructures were grown by atmospheric pressure-metal organic vapor phase epitaxy (AP-MOVPE). Compositional intermixing of As/P and Ga/In near the heterointerfaces was studied by photoluminescence (PL) spectroscopy. Indium segregation, memory effect of In into GaAs and the carry-over of As in the GaInP layer during the growth process were considered as three major factors giving rise to the anomalous emissions in the PL spectra. Both thermal annealing and zinc doping strongly enhanced the compositional interdiffusion near the heterointerfaces.