GaN Films (gan + film)

Distribution by Scientific Domains

Kinds of GaN Films

  • plane gan film


  • Selected Abstracts


    Single ZnO Nanowire/p-type GaN Heterojunctions for Photovoltaic Devices and UV Light-Emitting Diodes

    ADVANCED MATERIALS, Issue 38 2010
    Ya-Qing Bie
    We fabricate heterojunctions consisting of a single n-type ZnO nanowire and a p-type GaN film. The photovoltaic effect of heterojunctions exhibits open-circuit voltages ranging from 2 to 2.7 V, and a maximum output power reaching 80 nW. Light-emitting diodes with UV electroluminescence based on the heterojunctions are demonstrated. [source]


    Nanowire-Templated Epitaxial Growth: Nanowire-Templated Lateral Epitaxial Growth of Low-Dislocation Density Nonpolar a -Plane GaN on r -Plane Sapphire (Adv. Mater.

    ADVANCED MATERIALS, Issue 23 2009
    23/2009)
    George Wang and co-workers report on p. 2416 that low dislocation density a -plane GaN films can be grown by the coalescence of vertically-aligned, single-crystalline GaN nanowires on lattice-mismatched r -plane sapphire. In this technique, shown by the artists' rendering on the inside cover, the nanowires facilitate dramatic strain relaxation in the suspended GaN film, leading to a large reduction in defects. [source]


    Deep levels associated with dislocation annihilation by Al pre-seeding and silicon delta doping in GaN grown on Si(111) substrates

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2008
    C. B. Soh
    Abstract The introduction of Si burst during the growth of GaN film on Si(111) substrate by MOCVD formed a Six Ny layer which leads to an effective reduction in the density of screw dislocations. The reduction is associated with bending of screw dislocations to form a square dislocation loop when neighbouring dislocations with opposite Burger's vector paired up. The concentration of electron traps Ec,Et ,0.17,0.26 eV which is associated with screw dislocations is substantially reduced and a kink is left at the silicon rich position. The mixed-edge dislocation, however, is not annihilated by the Six Ny layer. Addition of TMAl burst for the AlN growth leads to a substantial reduction in trap concentration associated with the nitrogen vacancies, VN, and antisite of nitrogen, NAl, at Ec,Et ,0.10 eV and Ec,Et , 0.60 eV respectively. This improves the quality of the subsequent layer of HT-GaN grown and is useful for device fabrication. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    The nucleation of HCl and Cl2 -based HVPE GaN on mis-oriented sapphire substrates

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010
    Tim Bohnen
    Abstract The nucleation of both classic HCl-based and novel Cl based HVPE GaN on mis-oriented sapphire substrates was investigated. The use of Cl2in HVPE increases the growth rate by a factor of 4-5 and strongly reduces the parasitic deposition, allowing for the growth of much thicker wafers than HCl-based HVPE. Morphological SEM surface studies of the HCl-based HVPE sample surface show that at 600 C a nanocrystalline layer is deposited on the sapphire. During the subsequent annealing phase, the morphology changes to a ,m-sized island structure. During overgrowth at 1080 C, the islands coalesce. Small voids or pinholes are then formed in between the coalescing GaN islands. These pinholes lead to numerous pits on the surface of the GaN at thicknesses of 5 ,m. The pits disappear during continued overgrowth and can no longer be found on the surface, when the GaN film reaches a thickness of 45 ,m. This particular coalescence mechanism also applies to Cl2 -based HVPE GaN on sapphire ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Structural analysis of nitride-based LEDs grown on micro- and nano-scale patterned sapphire substrates

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010
    Y. K. Su
    Abstract The structural properties of nitride-based light-emitting diodes (LEDs) grown on micro- and nano-scale patterned sapphire substrates (PSS) were discussed in detail. The high resolution X-ray diffraction (HRXRD) and etch-pit density (EPD) results reveal that the crystalline quality of the epitaxial GaN film could be effectively improved by using the PSS technique, and depended on the aspect ratio of PSS. The crystalline quality of epitaxial GaN films grown on PSS-2,m and PSS-3,m was better than that of the LED grown on NPSS. The electrical characteristics and junction temperature results of the LED grown on micro-scale PSS were better compared with nano-scale PSS. But the output power of the LED grown on nano-scale PSS was larger than that of the LED grown on micro-scale PSS since the pattern-size of PSS is related to the capability of light extraction. However, when the spacing of PSS is less than 2 ,m, some voids formed at the GaN/sapphire interface may cause the thermal dissipation problem of LEDs. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    MOVPE high quality GaN film grown on Si (111) substrates using a multilayer AlN buffer

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
    Kung-Liang Lin
    Abstract High quality GaN films were successfully grown on Si (111) substrates using the MOVPE method and a multilayer AlN buffer. The buffer layer film quality and thickness are critical for the growth of the crack-free GaN film on Si (111) substrates. Cracks started to form on the single layer high temperature (HT) AlN film grown on Si (111) substrate as the AlN thickness was greater than 20 nm. However, a 100 nm crack-free AlN film can be obtained when multilayer buffer of HT-AlN/low temperature (LT)-AlN/HT-AlN was grown on the Si (111) substrate. By using multilayer AlN buffer, a 2 ,m crack-free GaN film was successful grown on the 2" Si (111) substrate. Moreover, the GaN film (2,m thick) grown on Si with a GaN (004) Mosaic FWHM of only 0.12. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Blue light emitting diode fabricated on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substrate

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
    Y. Naoi
    Abstract We studied the growth technique for the dislocation reduction in a-plane GaN grown by metal organic chemical vapour deposition (MOCVD) using AlInN buffer layer, high temperature atomic layer epitaxy, and trenched r-sapphire technique. By using these techniques, the crystal quality was much improved. We also fabricated blue light emitting diodes (LEDs) on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substrate. The electroluminescence (EL) characteristics of the LED samples were examined, and we found that the EL near field pattern from homo-epitaxially grown a-GaN based LED was spatially uniform, although the pattern from the LED on r-sapphire substrate was not uniform. The output power at the wavelength of 430nm was 0.72mW at the 20mA injection current for the sample on a-plane bulk GaN. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Structural and electrical characterization of a -plane GaN grown on a -plane SiC

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003
    M. D. Craven
    Abstract Planar nonpolar () a -plane GaN thin films were grown on () a -plane 6H-SiC substrates via metalorganic chemical vapor deposition by depositing a high temperature AlN buffer layer prior to the epitaxial GaN growth. The orientation of the GaN film and AlN buffer layer directly match that of the SiC substrate, as determined by on- and off-axis X-ray diffraction measurements. The morphological evolution of GaN grown on the AlN buffer layers was investigated using atomic force microscopy. Microstructural characterization of the coalesced a -plane GaN films provided by plan-view transmission electron microscopy revealed threading dislocation and stacking fault densities of ,3 1010 cm,2 and ,7 105 cm,1, respectively. Structural comparisons to a -plane GaN films grown on r -plane sapphire substrates are presented. Si-doped films were grown with a variety of Si/Ga ratios and electrically characterized using Hall effect measurements. A maximum Hall mobility of 109 cm2/Vs was attained at a carrier concentration of 1.8 1019 cm,3. [source]


    Recent Progress in GaN-Based Light-Emitting Diodes

    ADVANCED MATERIALS, Issue 45 2009
    Haiqiang Jia
    Abstract In the last few years the GaN-based white light-emitting diode (LED) has been remarkable as a commercially available solid-state light source. To increase the luminescence power, we studied GaN LED epitaxial materials. First, a special maskless V-grooved c -plane sapphire was fabricated, a GaN lateral epitaxial overgrowth method on this substrate was developed, and consequently GaN films are obtained with low dislocation densities and an increased light-emitting efficiency (because of the enhanced reflection from the V-grooved plane). Furthermore, anomalous tunneling-assisted carrier transfer in an asymmetrically coupled InGaN/GaN quantum well structure was studied. A new quantum well structure using this effect is designed to enhance the luminescent efficiency of the LED to ,72%. Finally, a single-chip phosphor-free white LED is fabricated, a stable white light is emitted for currents from 20 to 60,mA, which makes the LED chip suitable for lighting applications. [source]


    The Spatial Distribution of Threading Dislocations in Gallium Nitride Films

    ADVANCED MATERIALS, Issue 38-39 2009
    Michelle A. Moram
    Spatial analysis techniques are used to study threading dislocations (TDs) at the surfaces of a wide range of GaN films. In all films, the dislocation positions are consistent with a spatially random TD generation process followed by movement of dislocations, but are inconsistent with the spatial distribution of dislocations expected at island coalescence boundaries. [source]


    Nanowire-Templated Epitaxial Growth: Nanowire-Templated Lateral Epitaxial Growth of Low-Dislocation Density Nonpolar a -Plane GaN on r -Plane Sapphire (Adv. Mater.

    ADVANCED MATERIALS, Issue 23 2009
    23/2009)
    George Wang and co-workers report on p. 2416 that low dislocation density a -plane GaN films can be grown by the coalescence of vertically-aligned, single-crystalline GaN nanowires on lattice-mismatched r -plane sapphire. In this technique, shown by the artists' rendering on the inside cover, the nanowires facilitate dramatic strain relaxation in the suspended GaN film, leading to a large reduction in defects. [source]


    Polarized Raman scattering studies of nonpolar a -plane GaN films grown on r -plane sapphire substrates by MOCVD

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2006
    Haiyong Gao
    Abstract Nonpolar (110) a -plane GaN thin films were grown on r -plane (102) sapphire substrates by low-pressure metal organic chemical vapor deposition (MOCVD). The stress characteristics of the a -plane GaN films were investigated by means of polarized Raman scattering spectra in backscattering configurations. The experimental results show that there are strong anisotropic in-plane stresses within the epitaxial a -plane GaN films by calculating the corresponding stress tensors. The temperature dependence of Raman scattering spectra was studied in the range from 100 K to 550 K. The measurements reveal that the Raman phonon frequencies decrease with increasing temperature. The temperature at which nonpolar a -plane GaN films are strain free is discussed. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Identification of van Hove singularities in the GaN dielectric function: a comparison of the cubic and hexagonal phase

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2009
    C. Cobet
    Abstract We present a detailed analysis of interband transition structures in the dielectric function of GaN. The dielectric function of the stable wurtzite and the metastable zinc blende phase were determined by means of synchrotron spectroscopic ellipsometry in the spectral range between 3 eV and 20 eV where the most significant structures of the dielectric function are located. In the hexagonal case, both the ordinary and extraordinary dielectric tensor component was measured on GaN films with M -plane/[1 00] orientation. In a comparative discussion of the two hexagonal tensor components and the zinc blende dielectric function, all prominent absorption structures were assigned to specific interband transitions at high symmetry points in the Brillouin zone. The assignment considers the individual dipole transition probabilities depending on the crystal symmetry and the geometry of the measurement. Furthermore, a detailed theoretical band-to-band analysis of dielectric function features, published by Lambrecht et al. [1], was considered. In conclusion, we suggest a new labeling of absorption structures as used in classical III,V materials like GaAs, which reflects the origin of transition structures from specific points in the respective Brillouin zones. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Optically induced strain relaxation in anisotropically strained M -plane GaN films

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2008
    T. Flissikowski
    Abstract We study the anisotropic in-plane strain in M -plane GaN films by photoreflectance, photoluminescence, Raman, and time-resolved pump-and-probe spectroscopy. We find that a highly strained film partially relaxes, if it is pumped by an intense optical pulse. The strain relaxation can be observed by a shift of the E2 -Raman line to lower energies and by a shift of the fundamental interband transition energies in the photoreflectance spectra. The photoluminescence intensity of the exposed areas is significantly reduced as compared to the one for areas, which have not been exposed to the intense optical pulse. This suggests that the strain relaxation is connected to the introduction of defects, which can act as non-radiative recombination centers. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a -plane GaN

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006
    V. Darakchieva
    Abstract Generalized infrared spectroscopic ellipsometry was applied to study the vibrational properties of anisotropically strained a -plane GaN films with different thicknesses. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and strain-free frequency of the GaN A1(TO) mode. These results are compared with previous theoretical and experimental findings and discussed. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth of GaN on a -plane sapphire: in-plane epitaxial relationships and lattice parameters

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
    T. Paskova
    Abstract We have studied GaN films grown on a -plane sapphire substrates by both hydride vapor phase epitaxy (HVPE) and metalorganic vapor phase epitaxy (MOVPE). The in-plane orientation relationships between the epitaxial films and the substrate are determined to be [11,20]GaN , [0001]sapphire and [1,100]GaN , [1,100]sapphire in the HVPE growth, while [1,100]GaN , [0001]sapphire and [11,20]GaN , [1,100]sapphire are found in the MOVPE growth. The different orientation preferences are attributed to the atom termination of the sapphire surface determined by the substrate treatment used in the different growth methods. The effect of the lattice matches on the in-plane lattice parameters and strain anisotropy in the two cases is studied. ( 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Structural analysis of nitride-based LEDs grown on micro- and nano-scale patterned sapphire substrates

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010
    Y. K. Su
    Abstract The structural properties of nitride-based light-emitting diodes (LEDs) grown on micro- and nano-scale patterned sapphire substrates (PSS) were discussed in detail. The high resolution X-ray diffraction (HRXRD) and etch-pit density (EPD) results reveal that the crystalline quality of the epitaxial GaN film could be effectively improved by using the PSS technique, and depended on the aspect ratio of PSS. The crystalline quality of epitaxial GaN films grown on PSS-2,m and PSS-3,m was better than that of the LED grown on NPSS. The electrical characteristics and junction temperature results of the LED grown on micro-scale PSS were better compared with nano-scale PSS. But the output power of the LED grown on nano-scale PSS was larger than that of the LED grown on micro-scale PSS since the pattern-size of PSS is related to the capability of light extraction. However, when the spacing of PSS is less than 2 ,m, some voids formed at the GaN/sapphire interface may cause the thermal dissipation problem of LEDs. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Fabrication of light emitting diodes transferred onto different substrates by GaN substrate separation technique

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010
    Y. Kunoh
    Abstract We have successfully transferred GaN films grown on high crystalline quality GaN substrates onto different substrates, where we have developed a laser lift-off technique with a green laser and an absorption-enhanced InGaN layer as a sacrificial layer (a layer to absorb laser beams). We have also achieved an output power of 13.0 mW at 20 mA with a wavelength of approximately 410 nm and an external quantum efficiency of 21.6% for light emitting diodes transferred on Si substrates by using this method ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Trap states in n-GaN grown on AlN/sapphire template by MOVPE

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008
    T. Ito
    Abstract Using epitaxial AlN/sapphire templates, high crystalline quality GaN films are grown on them by metal organic chemical vapour deposition. The electron traps behaviour of these GaN films were observed by deep level transient spectroscopy (DLTS). Four distinct trap levels were ob-served in both n-GaN grown on AlN/sapphire template and on conventional low temperature buffer layer (LT-BL)/sapphire. The magnitude the of the DLTS signal E1 and E2 were almost same. It suggests that E1 is not only associate with dislocation density but also other defect. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    MOVPE high quality GaN film grown on Si (111) substrates using a multilayer AlN buffer

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
    Kung-Liang Lin
    Abstract High quality GaN films were successfully grown on Si (111) substrates using the MOVPE method and a multilayer AlN buffer. The buffer layer film quality and thickness are critical for the growth of the crack-free GaN film on Si (111) substrates. Cracks started to form on the single layer high temperature (HT) AlN film grown on Si (111) substrate as the AlN thickness was greater than 20 nm. However, a 100 nm crack-free AlN film can be obtained when multilayer buffer of HT-AlN/low temperature (LT)-AlN/HT-AlN was grown on the Si (111) substrate. By using multilayer AlN buffer, a 2 ,m crack-free GaN film was successful grown on the 2" Si (111) substrate. Moreover, the GaN film (2,m thick) grown on Si with a GaN (004) Mosaic FWHM of only 0.12. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Sidewall epitaxial lateral overgrowth of nonpolar a-plane GaN by metalorganic vapor phase epitaxy

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
    Daisuke Iida
    Abstract A major obstacle to achieving high-performance devices using nonpolar a-plane and m-plane GaN is the existence of high-density threading dislocations and stacking faults. Low-defect-density nonpolar plane GaN films were previously grown by sidewall epitaxial overgrowth using metalorganic vapor phase epitaxy [1, 2]. In this study, we control the growth-rate ratio of Ga-polar GaN to N-polar GaN by adjusting the V/III ratio. It is possible to grow GaN only from the N-face sidewall of grooves by maintaining a high V/III ratio, which reduces the number of coalescence regions on grooves and decreases the threading-dislocation density and stacking-fault density. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Comparison of deep level incorporation in ammonia and rf-plasma assisted molecular beam epitaxy n-GaN films

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
    A. R. Arehart
    Abstract The use of rf-plasma and ammonia nitrogen sources for growth of GaN films by molecular beam epitaxy (MBE) are compared in terms of defect incorporation using deep level optical spectroscopy (DLOS) and deep level transient spectroscopy (DLTS). To better improve the understanding of ammonia-based MBE growth of GaN and potential defect sources as opposed to the more studied plasma source-based MBE-grown material several V/III ratios were also investigated, which were generated via systematic adjustment of the ammonia flow rates during growth. The DLOS spectra, comparing deep traps within the n-GaN grown using N-plasma and ammonia sources, reveal the presence of the same deep levels due to background carbon and gallium vacancies, with energy levels at EC -3.28, EC -2.62, and EC -1.28. The DLTS results of the N-plasma and ammonia-based MBE samples show two similarly dominant electron traps at EC -0.60, and EC -0.24 in each sample. Measurements made as a function of V/III flux ratio for ammonia-based MBE growth indicate a large dependence of the EC -0.24 eV trap concentration on growth flux ratio, which is significant for guiding continued optimization of this promising MBE growth method for GaN devices. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Realization of AlGaN/GaN HEMTs on 3C-SiC/Si(111) substrates

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
    Y. Cordier
    Abstract Cubic SiC/Si (111) template is an interesting alternative for growing GaN on silicon. As compared with silicon, this substrate allows reducing the stress in GaN films due to both lower lattice and thermal expansion coefficient mismatch, and can provide better heat dissipation. In this work, we first developed the epitaxial growth of 3C-SiC films on 50 mm Si(111) substrates using chemical vapor deposition. AlGaN/GaN high electron mobility transistors were grown by molecular beam epitaxy on these films. Both the structural quality and the behavior of transistors realized on these structures show the feasibility of this approach. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Optical properties of InGaN/GaN MQW microdisk arrays on GaN/Si(111) template

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
    Kang Jea Lee
    Abstract We report the fabrication of InGaN/GaN multi quantum well (MQW) microdisk arrays on Si(111) substrates. InGaN/GaN MQWs were grown on highly tensile-strained GaN films on Si(111) substrate by metalorganic chemical vapor deposition. Microdisk resonators were fabricated using a combination of optical lithography, a dry GaN-etching process, and Si undercut etching by acid chemical solution. The evidence of whispering-gallery modes in optically pumped microdisk cavities have been observed by photoluminescence. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    In-plane anisotropy in uniaxially-strained GaN films detected by optical diffraction technique

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
    Satoru Adachi
    The cover picture of this issue of physica status solidi (c) has been taken from the article [1]. [source]


    Morphological evaluation of epitaxial GaN grown on r -plane sapphire by metalorganic vapor-phase epitaxy

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
    K. Kusakabe
    Abstract Morphological evaluation of epitaxial GaN films grown on r -plane sapphire substrates by atmospheric metalorganic vapor-phase epitaxy was investigated. The surface frequently showed rough morphology when the GaN was grown at conventional epitaxial conditions. It was found, however, that the surface roughness was improved by using appropriate combinations of growth temperature and low-temperature GaN buffer thickness. Thereby, a peak-to-valley value of the roughness was reduced from 4 ,m to 0.8 ,m. The rotation of crystallographic orientations was observed in the flattened GaN films. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Etch-pits and threading dislocations in thick LEO GaN films on sapphire grown by MOCVD

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2004
    Lu Min
    Abstract High quality Lateral Epitaxial Overgrowth (LEO) GaN films on (0001) sapphire substrates were grown by a commercial MOCVD system (Thomas Swan Corp.). We have studied the etch-pits and threading dislocations in GaN films by wet etching of pits, HCl vapor etching of pits and Scanning Electron Microscope (SEM). SEM images of GaN films etched in HCl vapor and molten KOH gave us notably different etching pits densities in the different region of LEO GaN films, which confirmed HCl vapor etching could show three kinds of Threading Dislocations (TDs), while molten KOH wet etching only could show pure screw TDs. In region above window TDs density is high (about 3 108/cm2) and edge TDs are in the majority, while it is almost free of TDs in region above mask, and only in middle region above mask there are some TDs (including all three kinds) and also edge TDs are in the majority. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Direct observation of hillocks on pendeo-epitaxial GaN films and stabilization of GaN seed layers for hillock-free surface

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003
    H. S. Cheong
    Abstract Hillocks formed on pendeo-epitaxial GaN (PE-GaN) films grown by metalorganic chemical vapor deposition were observed by scanning electron microscopy, atomic force microscopy and high-resolution transmission electron microscopy. In order to suppress hillock formation on PE-GaN films, a two-step growth technique was employed. In the first-step growth, whose growth temperature and V/III ratio were relatively low, it was necessary to suppress hillock formation on the surface, and reduce the crystallographic tilt in the wing regions of PE-GaN films. In the second-step growth, whose growth temperature and V/III ratio were relatively high, complete coalescence without tilt in the wing regions was achieved by a high lateral growth rate. [source]


    Structural and electrical characterization of a -plane GaN grown on a -plane SiC

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003
    M. D. Craven
    Abstract Planar nonpolar () a -plane GaN thin films were grown on () a -plane 6H-SiC substrates via metalorganic chemical vapor deposition by depositing a high temperature AlN buffer layer prior to the epitaxial GaN growth. The orientation of the GaN film and AlN buffer layer directly match that of the SiC substrate, as determined by on- and off-axis X-ray diffraction measurements. The morphological evolution of GaN grown on the AlN buffer layers was investigated using atomic force microscopy. Microstructural characterization of the coalesced a -plane GaN films provided by plan-view transmission electron microscopy revealed threading dislocation and stacking fault densities of ,3 1010 cm,2 and ,7 105 cm,1, respectively. Structural comparisons to a -plane GaN films grown on r -plane sapphire substrates are presented. Si-doped films were grown with a variety of Si/Ga ratios and electrically characterized using Hall effect measurements. A maximum Hall mobility of 109 cm2/Vs was attained at a carrier concentration of 1.8 1019 cm,3. [source]


    Formation of "air-gap" structure at a GaN epilayer/substrate interface by using an InN interlayer

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003
    A. Yamamoto
    Abstract We propose a new technique for "air-gap" formation at a GaN/sapphire interface by using an InN interlayer. This is aimed to grow epitaxial GaN films with reduced stress and cracks. First, an InN interlayer of about 0.2 ,m thick is grown at 600 C in atmospheric pressure. Then a 30 nm-thick GaN buffer layer is grown on the InN layer at 550 C. The substrate temperature is ramped up to 1000 C in the NH3 flow, and finally a 1.5 ,m-thick GaN epilayer is grown on the annealed GaN buffer layer using nitrogen carrier gas. Consequently, an "air-gap" structure is naturally formed close to the substrate surface. During the ramping period of substrate temperature, the InN layer decomposes due to its thermal instability and metallic In is formed. It is found that metallic In drops as a result of InN decomposition contribute to the air-gap formation. No cracks are found on the GaN surface and a reduced stress in the layer is confirmed by PL and Raman shift measurements. ( 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]