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AlGaN Layers (algan + layer)
Selected AbstractsSpatially resolved X-ray diffraction as a tool for strain analysis in laterally modulated epitaxial structuresCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2009A. Wierzbicka Abstract Spatially resolved X-ray diffraction (SRXRD) is applied for micro-imaging of strain in laterally modulated epitaxial structures. In GaAs layers grown by liquid phase epitaxial lateral overgrowth (ELO) on SiO2 -masked GaAs substrates a downward tilt of ELO wings caused by their interaction with the mask is observed. The distribution of the tilt magnitude across the wings width is determined with ,m-scale spatial resolution. This allows measuring of the shape of the lattice planes in individual ELO stripes. If a large area of the sample is studied the X-ray imaging provides precise information on the tilt of an individual wing and its distribution. In heteroepitaxial GaSb/GaAs ELO layers local mosaicity in the wing area is found. By the SRXRD the size of microblocks and their relative misorientation were analyzed. Finally, the SRXRD technique was applied to study distribution of localized strain in AlGaN epilayers grown by MOVPE on bulk GaN substrates with AlN mask. X-ray mapping proves that by mask patterning strain in AlGaN layer can be easily engineered, which opens a way to produce thicker, crack-free AlGaN layers with a higher Al content needed in GaN-based laser diodes. All these examples show that high spatial and angular resolutions offered by SRXRD makes the technique a powerful tool to study local lattice distortions in semiconductor microstructures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] X-ray diffraction reciprocal lattice space mapping of a -plane AlGaN on GaNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006Michinobu Tsuda Abstract In this study, the anisotropic strain in a -plane AlGaN on GaN was investigated by X-ray diffraction (XRD) analysis using AlGaN/GaN heterostructure grown on r -plane sapphire. An a -plane GaN layer is compressively strained, particularly in the m -axis direction. According to XRD reciprocal lattice space mapping, the AlGaN layer was strained under tensile stress and grown almost coherently to the underlying GaN layer. The tensile stress in the AlGaN layer in the c -axis direction is approximately 1.7 times larger than that in the m -axis direction. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spatially resolved cathodoluminescence study on AlGaN layer fabricated by air-bridged lateral epitaxial growthPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004Akihiko Ishibashi Abstract Structural properties of AlGaN layer on the GaN seed layer fabricated by air-bridged lateral epitaxial growth (ABLEG) have been studied by spatially resolved cathodoluminescence (CL) microscopy. The cross-sectional spatially resolved CL images of the ABLEG-AlGaN layer reveal that there are roughly three regions which have different main CL peaks. This result suggests that there are roughly three regions with the different Al contents. Before coalescence of the overgrown AlGaN wings, there are two regions of Al content, such as about 6.5, 10.6%. On the other hand, after coalescence of the wings, the Al content of the AlGaN layer becomes uniform (Al content = 8.9%). These results suggest that the facet growth of the overgrown AlGaN wings causes the modulation of Al content in the ABLEG-AlGaN layer. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thick crack-free AlGaN films deposited by facet-controlled epitaxial lateral overgrowthPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003R. Liu Abstract Thick crack-free AlGaN films have been grown on inclined-facet GaN templates. Light emitting diodes with , = 323 nm has been achieved on these epilayers. The GaN template was grown at a low temperature in order to obtain triangle-facet growth fronts. Subsequent growth of AlGaN on this template involving a lateral overgrowth process exhibits interesting properties. The microstructure and optical characterizations were done using transmission electron microscopy and cathodoluminescence. At the AlGaN/GaN interface, a high density of dislocations was created due to lattice mismatch strain. Another unexpected set of triangular boundaries was observed inside the AlGaN layer, which grew without any change of the growth parameters. These boundaries were found to arise from domains grown in different directions. Mono-chromatic cathodoluminescence images indicate that Al content is different between the vertically-grown and the laterally-grown domains, suggesting that lattice mismatch strain exists between them. Dislocations were created at these mismatched boundaries to relax the strain. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spatially resolved X-ray diffraction as a tool for strain analysis in laterally modulated epitaxial structuresCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2009A. Wierzbicka Abstract Spatially resolved X-ray diffraction (SRXRD) is applied for micro-imaging of strain in laterally modulated epitaxial structures. In GaAs layers grown by liquid phase epitaxial lateral overgrowth (ELO) on SiO2 -masked GaAs substrates a downward tilt of ELO wings caused by their interaction with the mask is observed. The distribution of the tilt magnitude across the wings width is determined with ,m-scale spatial resolution. This allows measuring of the shape of the lattice planes in individual ELO stripes. If a large area of the sample is studied the X-ray imaging provides precise information on the tilt of an individual wing and its distribution. In heteroepitaxial GaSb/GaAs ELO layers local mosaicity in the wing area is found. By the SRXRD the size of microblocks and their relative misorientation were analyzed. Finally, the SRXRD technique was applied to study distribution of localized strain in AlGaN epilayers grown by MOVPE on bulk GaN substrates with AlN mask. X-ray mapping proves that by mask patterning strain in AlGaN layer can be easily engineered, which opens a way to produce thicker, crack-free AlGaN layers with a higher Al content needed in GaN-based laser diodes. All these examples show that high spatial and angular resolutions offered by SRXRD makes the technique a powerful tool to study local lattice distortions in semiconductor microstructures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth kinetics of AlxGa1,xN layers (0 < x < 1) in plasma-assisted molecular beam epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010A. M. Mizerov Abstract Comparative study of growth kinetics of the AlxGa1-xN (x = 0-1) layers of different polarity, grown by plasma assisted molecular beam epitaxy (PA MBE) under different growth conditions (substrate temperature, group III to activated nitrogen and Al to Ga flux ratios) and on different buffer layers, is presented. The 60 °C higher temperature stability of N-face AlGaN layers is detected. The strong influence of elastic stress on growth kinetics of metal-polar AlxGa1-xN (x > 0.2) layers is observed and discussed. It was found that two-dimensional growth of AlGaN films of the same composition on different buffer layers at TS = 700 °C can be achieved at different group III surface enrichment, the AlGaN(0001)/c-Al2O3 films exhibiting the atomically smooth surface at group III to activated nitrogen flux ratio FIII/FN *gradually increased from 1.3 to 2 with the x variation from 0.1 to 0.8. In this case the alloy composition is controlled by the variation of Al flux only (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Piezoelectric actuation of all-nitride MEMSPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008K. Tonisch Abstract We present a MEMS technology based on (GaN/)AlGaN/GaN,heterostructures. Thereby the lower GaN layer represents the mechanical active layer, while the upper GaN and AlGaN layers supply the piezoelectrically active layers for actuation and the confinement of a 2D electron gas (at the lower interface). The 2DEG serves as back electrode for the piezoelectric actuation and as read,out, since it is modulated by the mechanical oscillation. The upper AlGaN and GaN layer both contribute to the total piezoelectric response, which was determined by piezoelectric force microscopy. The electrical field distribution throughout the heterostructure was determined by means of electroreflectance. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] AlGaN epitaxial layers grown by HVPE on sapphire substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006V. Soukhoveev Abstract Growth of AlxGa1,xN (x , 0.0-1.0) alloy layers by hydride vapor pahse epitaxy (HVPE) is reported. Crack-free undoped AlGaN layers from 0.1 to 2 ,m thick were grown on 2, SiC and 2,and 4, sapphire substrates. For AlxGa1,xN (x , 0.7-0.8) layers grown on sapphire, high-resolution symmetric/asymmetric X-ray diffraction (XRD) measurements resulted in ,-scan rocking curve widths ranging from 250 to 650 arcsec and from 1400 to 1900 arcsec, for the (00.2) and (10.2) reflections, respectively. Minimum XRD-estimated screw and edge dislocation densities in AlGaN layers grown on sapphire were <6 x 108 cm,2 and <2 x 109 cm,2, respectively. Raman studies revealed that the composition dependences of the phonon modes of HVPE-grown AlxGa1,xN layers are in a good agreement with the one, which have been observed for MOCVD-grown AlxGa1,xN alloys earlier. Grown layers had n-type electrical conductivity for the composition range up to x = 0.4. The layer became highly resistive for higher AlN contents. First results on 40 µm thick crack free AlGaN growth on SiC substrates are reported. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] n-Al0.75Ga0.25N epilayers for 250 nm emission ultraviolet light emitting diodesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005W. H. Sun Abstract We have developed a unique approach combining migration-enhanced metalorganic chemical vapor deposition (MEMOCVD) high temperature AlN buffer layers and AlGaN/AlN superlattices (SLs) to yield high quality ( HQ) AlGaN layers for 250 nm LEDs. Symmetric/asymmetric X-ray diffraction (XRD) and room temperature photoluminescence measurements were used to study the high-structural and optical quality. The (002) and (114) rocking curve full width at half,maximum (FWHM) of 1.4 µm n-Al0.75Ga0.25N grown over AlGaN/AlN buffer were 143 and 565 arcsec, respectively. Crack-free Al0.75Ga0.25N layers with electron concentration as high as 1 × 1018 cm,3 and Hall mobility about 50 cm2/V.s were successfully grown and used for sub-milliwatt power (0.12 mW at a pulse pump current of 300 mA) 250 nm deep ultraviolet light emitting diodes (UVLEDs). In addition, for comparison, we prepared n-AlGaN only using high temperature AlN without SLs inserted. The experiments show that the AlGaN/AlN SLs inserted play a crucial role in improving structural and optical quality of high Al-composition AlGaN epilayers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of indium incorporation in AlGaN on threading dislocation densityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005H. Kang Abstract A comparison of dislocation densities in AlGaN and InAlGaN with approximately similar alloy compositions was completed. A systematic series of the AlGaN layers with concentration of 17% Aluminum were grown by metal-organic chemical vapor deposition with trace amounts of indium incorporated into the layers. X-ray diffraction analysis by Williamson Hall plot and reciprocal space mapping was employed to investigate columnar structure in these layers. It was found that lateral coherence length, related to threading dislocation, was systematically varied with Indium content. The lateral coherence length increased with the consequence that the threading dislocation density decreased as Indium content increased, which indicated that even small amounts of indium incorporation could improve crystalline quality. The results are in good agreement with etch pit density study using AFM. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of oxygen incorporation in AlGaN/GaN heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003Ho Won Jang Abstract The unintentional doping of oxygen atoms in undoped AlGaN layers was demonstrated by scanning photoemission microscopy (SPEM) using synchrotron radiation. In-situ annealing at 1000 °C and subsequent SPEM imaging showed that the oxygen concentration in AlGaN was much higher than in GaN. Space-resolved photoemission spectra of O 1s, Ga 3d and Al 2p core levels showed that the predominant oxygen incorporation in AlGaN resulted from the formation of Al,O bonds due to the high reactivity of Al with oxygen. The degenerated AlGaN layer produced by the oxygen donors caused the tunneling-assisted transport of electrons at the interface of the AlGaN with metal contacts and an increase in the sheet carrier concentration at the AlGaN/GaN heterointerface. (© 2003 WILEY-VCH Verlag GmbH & Co. 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