bluuebunny/crossref_metadata_2025_split huggingface dataset:
Integration of PLZT and BST Family Oxides with GaN.
Authors: Osinsky Andrei V. , Fuflyigin Vladimir N. , Wang Feiling , Vakhutinsky Peter I. , Norris Peter E. 
Published: September 2012

AbstractRecent advances in the processing of complex-oxide materials has allowed us to monolithically grow ferroelectrics of lead lanthanum zirconate titanate (PLZT) and barium strontium titanate (BST) systems on a GaN/sapphire structure. High quality films of PLZT and BST were grown on GaN/c-Al2O3 in a thickness range of 0.3-5 [.proportional]m by a solgel technique. Field-induced birefringence, as large as 0.02, was measured from a PLZT layer grown on a buffered GaN/sapphire structure. UV illumination was found to result in more symmetrical electrooptic hysteresis loop. BST films on GaN demonstrated a low frequency dielectric constant of up to 800 with leakage current density as low as 5.5.10−8 A/cm2.
HVPE and MOVPE GaN Growth on Slightly Misoriented Sapphire Substrates
Authors: Parillaud Olivier , Wagner Volker , Bühlmann Hans-Jörg , Lelarge François , Ilegems Marc 
Published: September 2012

AbstractWe present preliminary results on gallium nitride growth by HVPE on C-plane sapphire with 2, 4 and 6 degrees misorientation towards M and A directions. A nucleation GaN buffer layer is deposited prior the growth by MOVPE. Surface morphology and growth rates are compared with those obtained on exact C-plane oriented sapphire, for various growth conditions. As expected, the steps already present on the substrate surface help to initiate a directed step-flow growth mode. The large hillocks, which are typical for HVPE GaN layers on (0001) sapphire planes, are replaced by more or less parallel macro-steps. The width and height of these steps, due to step bunching effect, depend directly on the angle of misorientation and on the growth conditions, and are clearly visible by optical or scanning electron microscopy. Atomic force microscopy and X-ray diffraction measurements have been carried out to quantify the surface roughness and crystal quality.
Hydride Vapour Phase Homoepitaxial Growth of GaN on MOCVD-Grown ‘Templates’
Authors: Paskova T. , Tungasmita S. , Valcheva E. , Svedberg E.B. , Arnaudov B. , Evtimova S. , Persson P.Å , Henry A. , Beccard R. , Heuken M. , Monemar B. 
Published: September 2012

AbstractWe report on an improved quality of thick HVPE-GaN grown on MOCVD-GaN ‘template’ layers compared to the material grown directly on sapphire. The film-substrate interface revealed by cathodoluminescence measurements shows an absence of highly doped columnar structures which are typically present in thick HVPE-GaN films grown directly on sapphire. This improved structure results in a reduction of two orders of magnitude of the free carrier concentration from Hall measurements. It was found that the structure, morphology, electrical and optical properties of homoepitaxial thick GaN layers grown by HVPE were strongly influenced by the properties of the MOCVD-GaN ‘template’. Additionally the effect of Si doping of the GaN buffer layers on the HVPEGaN properties was analysed.
Visible and Infrared Emission from GaN:Er Thin Films Grown by Sputtering
Authors: Chen Hong , Gurumurugan K. , Kordesch M.E. , Jadwisienczak W.M. , Lozykowski H.J. 
Published: September 2012

AbstractErbium-doped films were grown on sapphire and silicon substrates by reactive sputtering, with different Er concentrations in the film. GaN films deposited at 800 K were determined to be polycrystalline by x-ray diffraction analysis, and retained their polycrystalline structure after annealing in nitrogen at 1250 K. The Er-doped films showed optical transmission beginning at about 360 nm, and the Er dose and film purity were determined with Rutherford backscattering spectroscopy. Photoluminescence and cathodoluminescence spectroscopy showed sharp emission lines corresponding to Er 3+ intra 4fn shell transitions over the range from 9 – 300 K. At above-bandgap optical and electron excitation, the 4S3/2 and 4F9/2 transition dominate, and are superposed on the “yellow band” emission. The infrared emission line at 1543 nm, corresponding to the Er 4I⅓ to 4I3/2 transition is also observed.
Growth and Characterization of GaN Thin Films on Si(111) Substrates Using SiC Intermediate Layer
Authors: Lim K. Y. , Lee K. J. , Park C. I. , Kim K.C. , Choi S. C. , Lee W.-H. , Suh E.-K. , Yang G. M. , Nahm K. S. 
Published: September 2012

AbstractGaN films have been grown atop Si-terminated 3C-SiC intermediate layer on Si(111) substrates using low pressure metalorganic chemical vapor deposition (LP-MOCVD). The SiC intermediate layer was grown by chemical vapor deposition (CVD) using tetramethylsilane (TMS) as the single source precursor. The Si terminated SiC surface was obtained by immediately flow of SiH4 gas after growth of SiC film. LP-MOCVD growth of GaN on 3C-SiC/Si(111) was carried out with trimethylgallium (TMG) and NH3. Single crystalline hexagonal GaN layers can be grown on Si terminated SiC intermediate layer using an AlN or GaN buffer layer. Compared with GaN layers grown using a GaN buffer layer, the crystal qualities of GaN films with AlN buffer layers are extremely improved. The GaN films were characterized by x-ray diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). Full width at half maximum (FWHM) of double crystal x-ray diffraction (DCXD) rocking curve for GaN (0002) on 3C-SiC/Si(111) was 890 arcsec. PL near band edge emission peak position and FWHM at room temperature are 3.38 eV and 79.35 meV, respectively.
Optical Properties of Manganese Doped Amorphous and Crystalline Aluminum Nitride Films
Authors: Caldwell M.L. , Richardson H.H. , Kordesch M.E. 
Published: September 2012

AbstractAn aluminum nitride (AlN) film deposited on silicon (100) was used as the substrate for growing manganese (Mn) doped AlN film by metal organic chemical vapor deposition (MOVCD). The (15.78 [.proportional]m) under layer of AlN was grown at 615°C at a pressure of 10−4 Torr. The (2.1 [.proportional]m) top layer of Mn-AlN was grown at the same temperature and pressure but doped with pulse valve introduction of the manganese decacarbonyl (100 ms on, 100 ms off). The film was then characterized ex situ with IR reflectance microscopy, X-ray diffraction, scanning electron microscopy imaging, cathodoluminescence, and X-ray fluorescence. The IR reflectance measurements showed a strong (A1) LO mode for AlN at 920 cm−1 and 900 cm−1 with a shoulder at 849 cm−1. X-ray Diffraction yielded three diffraction peaks at a 2ø position of 33, 36 and 38 degrees corresponding to 100, 002, and 101 lattice planes respectively. Cathodoluminescence results show strong visible emitted light from incorporated manganese. The relative percentage of manganese to aluminum was below the detection limit (0.01 %) of the Xray fluorescence spectrometer. Amorphous Mn doped AlN films have also been grown using a low temperature atomically abrupt sputter epitaxial system. The amorphous Mn doped AlN showed no cathodoluminescence.
Surface Morphology of GaN: Flat Versus Vicinal Surfaces
Authors: Xie M.H. , Seutter S.M. , Zheng L.X. , Cheung S.H. , Ng Y.F. , Wu Huasheng , Tong S.Y. 
Published: September 2012

AbstractThe surface morphology of GaN films grown by molecular beam epitaxy (MBE) is investigated by scanning tunneling microscopy (STM). A comparison is made between flat and vicinal surfaces. The wurtzite structure of GaN leads to special morphological features such as step pairing and triangularly shaped islands. Spiral mounds due to growth at screw threading dislocations are dominant on flat surfaces, whereas for vicinal GaN, the surfaces show no spiral mound but evenly spaced steps. This observation suggests an effective suppression of screw threading dislocations in the vicinal films. This finding is confirmed by transmission electron microscopy (TEM) studies. Continued growth of the vicinal surface leads to step bunching that is attributed to the effect of electromigration.
Growth of InN by MBE
Authors: Chen W.-L. , Gunshor R. L. , Han Jung , Higashimine K. , Otsuka N. 
Published: September 2012

AbstractA series of experiments were performed to explore the growth of InN by Molecular Beam Epitaxy (MBE). The growth conditions were optimized based on the study of RHEED during growth and InN dissociation experiments. Characterization of the InN thin films were performed by various techniques such as TEM and XRD.
The Effect of the Buffer Layer on the Structure, Mobility and Photoluminescence of MBE grown GaN
Authors: Sharma Nikhil , Tricker David , Keast Vicki , Hooper Stewart , Heffernan Jon , Barnes Jenny , Kean Alistair , Humphreys Colin 
Published: September 2012

AbstractAlthough GaN has been grown mainly by metal organic chemical vapour deposition (MOCVD), molecular beam epitaxy (MBE) offers the advantages of lower growth temperatures and a more flexible control over doping elements and their concentrations [1]. We are growing GaN by MBE on sapphire substrates, using a GaN buffer layer to reduce the misfit strain, thus improving the structural quality of the epilayer. The quality of the GaN epilayers (in terms of their photoluminescence, mobility and structure) has been investigated as a function of the buffer layer thickness and annealing time.The investigation showed that increasing the buffer layer thickness improved the mobility of the material because the defect density in the GaN epilayer decreased. Optical characterisation showed that the ratio of the donor band exciton (DBE) peak (3.47eV) to the structural peak (3.27eV) in the photoluminescence spectrum, measured at 10K, increased with decreasing defect density. The unwanted structural peak can be considered to originate from a shallow donor to a shallow acceptor transition, which is clearly related to the structural defects in GaN. Thus by increasing the buffer layer thickness and annealing time the structural quality, mobility and photoluminescence improves in the GaN epilayers.Structural characterisation by transmission electron microscopy (TEM) showed that the observed increase in the DBE to structural peak ratio in the photoluminescence spectra could be correlated with a decrease in the density of stacking faults in the GaN epilayers. The detailed structure of these stacking faults was investigated by dark field and high resolution TEM. Their effect on the electrical and optical behaviour of GaN may be assessed by determining the local change in the dielectric function in the vicinity of individual stacking faults.
MBE Growth of GaN Films in Presence of Surfactants: The Effect of Mg and Si
Authors: Mula Guido , Daudin Bruno , Adelmann Christoph , Peyla Philippe 
Published: September 2012

AbstractWe present here a description and an analysis of the modifications in the growth behaviour of GaN induced by the presence of foreign species. The particular cases of Mg and Si are analysed. Profound changes, both in microscopic and macroscopic scales, occur in presence of Mg, even for fluxes of about 1/1000th of the Ga flux. The growth rate can be increased by almost 50%, depending of the III/V ratio and on the amount of Mg. A theoretical model is proposed to describe the observed effect. It is found that Mg induces changes in the Ga and N diffusion barriers and acts as a surfactant. The effect is stronger on the a-GaN than on the α-GaN, where N is more tightly bonded. The effect of Si is by far less pronounced, probably because it is more easily incorporated than Mg, and its effect on the surface kinetics is then strongly reduced.
Role of Arsenic Hexagonal Growth-Suppression on a Cubic GaNAs Growth Using Metalorganic Chemical Vapor Deposition
Authors: Yoshida S. , Kimura T. , Wu J. , Kikawa J. , Onabe K. , Shiraki Y. 
Published: September 2012

AbstractThe hexagonal domain suppression-effects in cubic-GaNAs grown by metalorganic chemical-vapor deposition (MOCVD) is reported. A thin buffer layer (20 nm) was first grown on a substrate at 853 K using trimethylgallium and dimethylhydrazine (DMHy), and GaNAs samples were grown at different AsH3 flow rates (0 ∼ 450 µmol/min) at 1193 K. As a result, three types of surface morphologies were obtained: the first was a smooth surface (AsH3 = 0 µmol/min); the second was a mirrorlike surface having small and isotropic grains (AsH3 : 45 ∼ 225 µmol/min ); and the third involved threedimensional surface morphologies (above 450 µmol/min of AsH3 flow rate). Furthermore, it was confirmed using X-ray diffraction that the mixing ratio of hexagonal GaNAs in cubic GaNAs decreased with an increase of the AsH3 flow rate. We could obtain GaNAs having a cubic component of above 85% at AsH3 flow rates above 20 µmol/min. Therefore, the MOCVD growth method using AsH3 and DMHy was mostly effective for suppressing hexagonal GaNAs. It was observed that the photoluminescence intensity of GaNAs was decreased with increase of arsine flow rate.
Microstructure and Physical Properties of GaN Films on Sapphire Substrates
Authors: Chen Zhizhong , Zhang Rong , Zhu Jianming , Shen Bo , Zhou Yugang , Chen Peng , Li Weiping , Shi Yi , Gu Shulin , Zheng Youdou 
Published: September 2012

AbstractTransmission electron microscopy (TEM), x-ray diffraction (XRD), photoluminescence (PL) and Raman scattering measurements were applied to study the correlation between the microstructure and physical properties of the GaN films grown by light radiation heating metalorganic chemical vapor deposition (LRH-MOCVD), using GaN buffer layer on sapphire substrates. When the density of the threading dislocation (TD) increases about one order of magnitude, the yellow luminescence (YL) intensity is strengthened from negligible to two orders of magnitude higher than the band edge emission intensity. The full width of half maximum (FWHM) of the GaN (0002) peak of the XRD rocking curve was widened from 11 min to 15 min, and in Raman spectra, the width of E2 mode is broadened from 5 cm-1 to 7 cm-1. A “zippers” structure at the interface of GaN/sapphire was observed by high-resolution electron microscope (HREM). Furthermore the origins of TD and relationship between physical properties and microstructures combining the growth conditions are discussed.
Structural Properties of (GaIn)(AsN)/GaAs MQW Structures Grown by MOVPE
Authors: Giannini C. , Carlino E. , Tapfer L. , Höhnsdorf F. , Koch J. , Stolz W. 
Published: September 2012

AbstractIn this work, we investigate the structural properties of (GaIn)(AsN)/GaAs multiplequantum wells (MQW) grown at low temperature by metalorganic vapour phase epitaxy. The structural properties, in particular the In- and N-incorporation, the lattice strain (strain modulation), the structural perfection of the metastable (GaIn)(AsN) material system and the structural quality of the (GaIn)(AsN)/GaAs interfaces are investigated by means of high-resolution x-ray diffraction, transmission electron microscopy (TEM), and secondary ion mass spectrometry. We demonstrate that (GaIn)(AsN) layers of high structural quality can be fabricated up to lattice mismatches of 4%. Our experiments reveal that N and In atoms are localized in the quaternary material and no evidences of In-segregation or N-interdiffusion could be found. TEM analyses reveal a low defect density in the highly strained layers, but no clustering or interface undulation could be detected. High-resolution TEM images show that (GaIn)(AsN)/GaAs interfaces are slightly rougher than GaAs/(GaIn)(AsN) ones.
Microstructral Investigations on GaN Films Grown by Laser Induced Molecular Beam Epitaxy
Authors: Zhou H. , Phillipp F. , Gross M. , Schröder H. 
Published: September 2012

AbstractMicrostructural investigations on GaN films grown on SiC and sapphire substrates by laser induced molecular beam epitaxy have been performed. Threading dislocations with Burgers vectors of 1/3<1120>, 1/3<1123> and [0001] are typical line defects, predominantly the first type of dislocations. Their densities are typically 1.5×1010 cm−2 and 4×109 cm−2 on SiC and sapphire, respectively. Additionally, planar defects characterized as inversion domain boundaries lying on {1100} planes have been observed in GaN/sapphire samples with an inversion domain density of 4×109 cm−2. The inversion domains are of Ga-polarity with respect to the N-polarity of the adjacent matrix. However, GaN layers grown on SiC show Ga-polarity. Possible reasons for the different morphologies and structures of the films grown on different substrates are discussed. Based on an analysis of displacement fringes of inversion domains, an atomic model of the IDB-II with Ga-N bonds across the boundary was deduced. High resolution transmission electron microscopy (HRTEM) observations and the corresponding simulations confirmed the IDB-II structure determined by the analysis of displacement fringes.
GaN Decomposition in Ammonia
Authors: Koleske D.D. , Wickenden A.E. , Henry R.L. 
Published: September 2012

AbstractGaN decomposition is studied as a function of pressure and temperature in mixed NH3 and H2 flows more characteristic of the MOVPE growth environment. As NH3 is substituted for the 6 SLM H2 flow, the GaN decomposition rate at 1000 °C is reduced from 1x1016 cm-2s-1 (i.e. 9 monolayers/s) in pure H2 to a minimum of 1x1014 cm-2s-1 at an NH3 density of 1x1019 cm-3. Further increases of the NH3 density above 1x1019 cm-3 result in an increase in the GaN decomposition rate. The measured activation energy, EA, for GaN decomposition in mixed H2 and NH3 flows is less than the EA measured in vacuum and in N2 environments. As the growth pressure is increased under the same H2 and NH3 flow conditions, the decomposition rate increases and the growth rate decreases with the addition of trimethylgallium to the flow. The decomposition in mixed NH3 and H2 and in pure H2 flows behave similarly, suggesting that surface H plays a similar role in the decomposition and growth of GaN in NH3.
Co-Doping Characteristics of Si and Zn with Mg in P-Type GaN
Authors: Kim K.S. , Oh C.S. , Han M.S. , Kim C.S. , Yang G.M. , Yang J.W. , Hong C.-H. , Youn C.J. , Lim K.Y. , Lee H.J. 
Published: September 2012

AbstractWe investigated the doping characteristics of Mg doped, Mg-Si co-doped, and Mg-Zn codoped GaN films grown by metalorganic chemical vapor deposition. We have grown p-GaN film with a resistivity of 1.26 Ωm and a hole density of 4.3 × 1017 cm−3 by means of Mg-Si co-doping technique. The Mg-Si co-doping characteristic was also explained effectively by taking advantage of the concept of competitive adsorption between Mg and Si during the growth. For Mg-Zn co-doping, p-GaN showing a low electrical resistivity (0.7 Ωm) and a high hole concentration (8.5 × 1017 cm−3) was successfully grown without the degradation of structural quality of the film. Besides, the measured specific contact resistance for Mg-Zn co-doped GaN film is 5.0 × 10−4 cm2, which is lower value by one order of magnitude than that for only Mg doped GaN film (1.9 × 10−3 Ωm2).
Doping Dependence of the Thermal Conductivity of Hydride Vapor Phase Epitaxy Grown n-GaN/Sapphire (0001) Using a Scanning Thermal Microscope
Authors: Florescu D.I. , Asnin V.A. , Mourokh L.G. , Pollak Fred H. , Molnar R. J. 
Published: September 2012

AbstractWe have measured the doping concentration dependence of the room temperature thermal conductivity (κ) of two series ofn-GaN/sapphire (0001) fabricated by hydride vapor phase epitaxy (HVPE). In both setsndecreased linearly with log n, the variation being about a factor two decrease in κ for every decade increase inn. κ ≈ 1.95 W/cm-K was obtained for one of the most lightly doped samples (n= 6.9×1016cm−3), higher than the previously reported κ ≈ 1.7-1.8 W/cm-K on lateral epitaxial overgrown material [V.A. Asninet al, Appl. Phys. Lett. 75, 1240 (1999)] and κ κ 1.3 W/cm-K on a thick HVPE sample [E.K. Sichel and J.I. Pankove, J. Phys. Chem. Solids 38, 330 (1977)]. The decrease in the lattice component of κ due to increased phonon scattering from both the impurities and free electrons outweighs the increase in the electronic contribution to κ.
High Temperature Hardness of Bulk Single Crystal GaN
Authors: Yonenaga I. , Hoshi T. , Usui A. 
Published: September 2012

AbstractThe hardness of single crystal GaN (gallium nitride) at elevated temperature is measured for the first time and compared with other materials. A Vickers indentation method was used to determine the hardness of crack-free GaN samples under an applied load of 0.5N in the temperature range 20 - 1200°C. The hardness is 10.8 GPa at room temperature, which is comparable to that of Si. At elevated temperatures GaN shows higher hardness than Si and GaAs. A high mechanical stability for GaN at high temperature is deduced.
Fabrication and Characterization of GaN Junctionfield Effect Transistors
Authors: Zhang L. , Lester L. F. , Baca A. G. , Shul R. J. , Chang P. C. , Willison C. G. , Mishra U. K. , Denbaars S. P. , Zolper J. C. 
Published: September 2012

AbstractJunction field effect transistors (JFET) were fabricated on a GaN epitaxial structure grown by metal organic chemical vapor deposition. The DC and microwave characteristics, as well as the high temperature performance of the devices were studied. These devices exhibited excellent pinch-off and a breakdown voltage that agreed with theoretical predictions. An extrinsic transconductance (gm) of 48 mS/mm was obtained with a maximum drain current (ID) of 270 mA/mm. The microwave measurement showed an fr of 6 GHz and an fmax of 12 GHz. Both the ID and the gm were found to decrease with increasing temperature, possibly due to lower electron mobility at elevated temperatures. These JFETs exhibited a significant current reduction after a high drain bias was applied, which was attributed to a partially depleted channel caused by trapped electrons in the semi-insulating GaN buffer layer.
Probing Nitride Thin Films in 3-Dimensions using a Variable Energy Electron Beam
Authors: Trager-Cowan Carol , McColl D. , Sweeney F. , Grimson S. T. F. , Treguer J-F. , Mohammed A. , Middleton P. G. , Manson-Smith S. K. , O'Donnell K. P. , Stricht W. Van der , Moerman I. , Demeester P. , Wu M. F. , Vantomme A. , Zubia D. , Hersee S. D. 
Published: September 2012

AbstractIn this paper we illustrate the application of electron beam techniques to the measurement of strain, defect and alloy concentrations in nitride thin films. We present brief comparative studies of CL spectra of AlGaN and InGaN epilayers and EBSD patterns obtained from two silicon-doped 3 μm thick GaN epilayers grown on an on-axis (0001) sapphire substrate and a sapphire substrate misoriented by 10° toward the m-plane (1010).
The Atomic Structure of Extended Defects in GaN
Authors: Ruterana P. , Nouet G. 
Published: September 2012

AbstractGaN layers contain large densities (1010 cm−2) of threading dislocations, nanopipes, (0001) and { 1120 } stacking faults, and { 1010 } inversion domains. Three configurations have been found for pure edge dislocations, mainly inside high angle grain boundaries where the 4 atom ring cores can be stabilized. Two atomic configurations, related by a 1/6 < 1010 > stair rod dislocation, have been observed for the { 1120 } stacking fault in (Ga-Al)N layers. For the {1010} inversion domain boundaries, a configuration corresponding to the Holt model was observed, as well as another with no N-N or Ga-Ga bonds.