bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of Electron Energy Loss Spectroscopy and its Application to Threading Edge Dislocations in GaN
Authors: Fall C. J. , Jones R. , Briddon P. R. , Blumenau A. T. , Frauenheim T. , Heggie M. I. 
Published: April 2011

AbstractThe electronic structure of dislocations in GaN is controversial. Several experimental techniques such as carrier mobility studies and cathodoluminescence experiments have indicated that dislocations are charged while theoretical studies point to intrinsic states and/or point defect accumulation along the core as a source of electrical activity. Electron Energy Loss Spectroscopy (EELS) studies have the ability to probe the electronic structure of extended defects. Here we report rst principles calculations of the EELS spectrum applied to edge dislocations in GaN. It is found that the electrostatic potential at N atoms in the vicinity of the dislocation varies by the order of a volt and casts doubt on any simple interpretation of core loss spectroscopy. On the other hand, low loss spectroscopy leads directly to detailed information about any gap states. The low loss spectrum obtained by the theory is in good agreement with recent experimental work and indicates that threading dislocations in p-type GaN possess acceptor levels in the upper half of the gap.
Conductivity, photoconductivity and optical properties of amorphous GaN films
Authors: Koo A. , Lanke U. D. , Ruck B. J. , Brown S. A. , Reeves R. , Liem I. , Bittar A. , Trodahl H. J. 
Published: April 2011

AbstractIt has been predicted that amorphous GaN has a low density of states in the gap, and therefore has potential as a useful opto-electronic material in the blue-green spectral region. We have synthesised amorphous GaN films on various substrates by ion assisted deposition and investigated the effects of sample preparation conditions on the conducting and optical properties. The room temperature resistivity ρ0 of stoichiometric (Ga:N of 1:1) films is above 105 Ω cm, and these films exhibit a complex form for the temperature dependence of the resistivity. Films having an excess of Ga show a much lower ρ0. The optical absorption shows ar 0 band-gap of 3 eV, with the gap falling below that value when the amorphous network incorporates homopolar (Ga-Ga) bonds. The best films are thus transparent across the visible region with a low density of gap states, undetectable in optical absorption. The photoluminescence spectra obtained from these a-GaN films consist of a broad green light emission peaking at 528 nm. Preliminary photoconductivity measurements show sensitivity in the UV.
High-Temperature Hardness of Bulk Single-Crystal AlN
Authors: Yonenaga Ichiro , Nikolaev Andrey , Melnik Yuriy , Dmitriev Vladimir 
Published: April 2011

AbstractThe hardness of single-crystal aluminum nitride (AlN) 0.5-mm-thick wafers was measured at elevated temperatures and compared with that of other semiconductors. A Vickers indentation method was used to determine the hardness under an applied load of 0.5 – 5 N in the temperature range 20 - 1400°C. The average hardness was measured as 17.7 GPa at room temperature, harder than GaN and InN. The fracture toughness is 0.5 MPa•m1/2. AlN exhibits the hardness higher than that of GaN in the entire temperature range investigated. Up to about 1100°C, AlN maintains its hardness and thus, a high mechanical stability for AlN at elevated temperatures is deduced.
Mg related Defect Formation during MOVPE Growth of GaN based Films studied by Transmission Electron Microscopy
Authors: Kröger Roland , Figge Stephan , Böttcher Tim , Ryder Peter L. , Hommel Detlef 
Published: April 2011

AbstractP-type active incorporation of magnesium into the gallium nitride lattice is still a challenge for the realization of wide band gap light emitters. This work presents a detailed microstructural study of phenomena connected with the problem of Mg doping of films grown by metal organic vapor phase epitaxy. Transmission Electron Microscopy both in conventional and in high resolution mode are used to obtain a better understanding of the Mg related defect formation processes. It is shown that the defect formation never occurs instantaneously at the beginning of the doping but a defect free zone always precedes the onset of the defect formation. This effect cannot solely be addressed to the memory effect of the reaction chamber since it is found that the defect density oscillates during growth. A more detailed investigation reveals that segregation of Mg plays a crucial role in the formation of defects. The observations emphasize the fact that a critical surface concentration is necessary for the defects to form. Beside the known processes of inversion boundary formation it is found that small nitrogen polar GaN grains in GaN films are gradually increasing on the expense of Ga polar grains if a sufficiently high Mg coverage and film thickness is realized. This process is found to occur in alternating steps along the {1123} and {0001}planes.
Evaluation of (In,Ga)N Films as Optical Absorption Filters for Application in Integrated Fluorescence Detection Micro-Bioanalytical Systems
Authors: Chediak J. Alex , Kneissl Michael , Sands Timothy D. 
Published: April 2011

AbstractFluorescence detection in integrated micro-bioanalytical systems requires the selective exclusion of light from the excitation source (typically blue or UV) and transmission of the longer wavelength fluorescence signal. In the present research, the application of (In,Ga)N alloy thin films as optical filters for absorption of blue (470 nm) and transmission of green (530 nm) has been evaluated. Absorption spectra, photoluminescence (PL) and Rutherford backscattering spectroscopy (RBS) results are presented for 200-400 nm (In,Ga)N thin films grown by MOCVD on sapphire substrates with 2-4 μm GaN buffer layers. A sigmoidal function was used to model the absorption coefficient of (In,Ga)N as a function of energy, Eg, and the broadening (ΔE) associated with the Urbach tail. Experimental data showed that, as expected, the absorption band edge for (In,Ga)N films broadened with increasing InN mole%. An increase in ΔE of 35 meV was observed when the InN mole% was increased from 10 to 16%. The sigmoidal function model provided a good fit to the experimental data, which allowed the experimental data to be extrapolated to higher InN concentrations. Based on this analysis, it is predicted that a 5 μm thick In0.22Ga0.78N film should transmit 50% of green light (530 nm) and only 3.29 x 1 0-4 of blue light (470 nm). The (In,Ga)N films that have been evaluated range in InN mole% from ~2-16%. The higher InN mole% samples (10-16%) can successfully filter lower wavelengths (e.g., 400 nm). For a filter application, it is also important that photoluminescence be effectively suppressed. In MQW structures, high PL intensity is often obtained by means of InN segregation (InN-rich nanoclusters). But for our evaluation with 200-400 nm (In,Ga)N films, relaxation of coherency strain results in large densities of dislocations, and correspondingly low PL intensity.
Electrical Properties of GaN/InGaN MQW Heterojunction Diodes as Affected by Various Plasma Treatments
Authors: Kim J. , Luo B. , Mehandru R. , Ren F. , Lee K. P. , Pearton S.J. , Polyakov A.Y. , Smirnov N.B. , Govorkov A.V. , Osinsky A.V. , Norris P.E. 
Published: April 2011

AbstractEffects of UV/O3 or deuterium plasma treatment, of annealing in air at 550°C, of annealing in N2 at 500°C and various combinations of these treatments on leakage current and resistance in the forward direction of GaN/InGaN multiquantum-well light emitting diodes MQW LEDs were studied. It was shown that the best results are achieved with 5 minutes long UV/O3 treatment. LED structures thus prepared showed effects of strong tunneling in their I-V characteristics. The space charge region was shown to be located in the GaN/InGaN superlattice SL. Passing of moderately high forward current through the structure for several hours enhanced the overall tunneling through the structure and facilitated faster tunneling between the layers in the GaN/InGaN SL.
Electrical Properties of n-GaN/p-SiC and n-AlGaN/p-SiC Heterojunction Diodes
Authors: Luo B. , Kim J. , Mehandru R. , Ren F. , Lee K. P. , Pearton S.J. , Polyakov A.Y. , Smirnov N.B. , Govorkov A.V. , Kozhukhova E.A. , Osinsky A.V. , Norris P.E. 
Published: April 2011

AbstractProperties of n-GaN/p-SiC and n-AlGaN/p-SiC heterojunctions prepared by HVPE on 4H SiC substrates were studied by means of C-V, C/G-T, C-f, I-V and DLTS. It is shown, in agreement with earlier publications, that the GaN/p-SiC HJ is staggered type II with ΔEc=-0.4 eV andΔEv=0.6 eV. Whenchanging GaN for AlGaN with Al mole fraction of x=0.25-0.3 the band alignment becomes normal type I with ΔEc=0.2 eV andΔEv=0.6 eV. I-V characteristics of both heterojunctions bear evidence of strong tunneling via defect states, particularly centers with activation energy of 1.25 eV for GaN/4H SiC HJ. The tunneling was found to be more pronounced in the AlGaN/SiC HJs even though these HJs showed no evidence of formation of dark line defects at the interface, in contrast to GaN/SiC. DLTS measurements on both types of HJs revealed the presence of broad bands whose behavior is indicative of these bands being related to continuous states in the gap, most likely near the nitride/carbide interface.
Effect of Ge in Cl2 Plasma for Reactive Ion Etching of GaN
Authors: Urushido Tatsuhiro , Yoshida Harumasa , Miyake Hideto , Hiramatsu Kazumasa 
Published: April 2011

AbstractWe investigated the effect of Ge and Si in Cl2 plasma on reactive ion etching (RIE) of GaN. The etched surfaces of GaN were smooth, and high etch rates of 0.63 m/min and 0.41 m m/min were obtained using a Ge plate and a Si plate, respectively. A rough surface was formed for the quartz plate without the Ge plate or Si plate. Optical emission spectroscopy revealed optical emissions related to GeClx+ions in Cl2 plasma with the Ge plate, to SiClx+ ions with the Si plate and to Cl+ ions without the Ge or the Si plate. It is considered that the GeClx+ions and SiClx+ ions for RIE of GaN plays an important role in obtaining a smooth etched surface of GaN, and that the high-energy Cl+ ion severely damages the GaN surface.
Fabrication and Investigation of the Metal-Ferroelectric-Semiconductor Structure with Pb(Zr0.53Ti0.47)O3 on AlxGa1-xN/GaN Heterostructures
Authors: Shen B. , Li W. P. , Wang X. S. , Yan F. , Zhang R. , Bi Z. X. , Shi Y. , Liu Z. G. , Zheng Y. D. , Someya T. , Arakawa Y. 
Published: April 2011

AbstractAn AlxGa1-xN/GaN-based metal-ferroelectric-semiconductor (MFS) structure is developed by depositing a Pb(Zr0.53Ti0.47)O3 film on a modulation-doped Al0.22Ga0.78N/GaN heterostructure. In high-frequency capacitance-voltage (C-V) measurements, the sheet concentration of the two-dimensional electron gas at the Al0.22Ga0.78N/GaN interface in the MFS structure decreases from 1.56 × 1013cm-2to 5.6 × 1012cm-2under the –10 V applied bias. A ferroelectric C-V window of 0.2 V in width near –10V bias is observed, indicating that the AlxGa1-xN/GaN MFS structure can achieve memory performance without the reversal of the ferroelectric polarization. The results indicate that AlxGa1-xN/GaN heterostructures are promising semiconductor channel candidates for MFS field effect transistors.
Extraction of Polarization-Induced Charge Density in Modulation-Doped AlxGa1-xN/GaN Heterostructures Based on Schottky C-V Simulation
Authors: Zhou Y.G. , Shen B. , Yu H.Q. , Liu J. , Zhou H.M. , Zhang R. , Shi Y. , Zheng Y.D. , Someya T. , Arakawa Y. 
Published: April 2011

AbstractA method based on Schottky capacitance-voltage (C-V) simulation was developed to extract the polarization-induced charge density in modulation-doped AlxGa1-xN/GaN heterostructures. There are two characteristic slopes in the experimental and simulated C-V curves.The influences of the polarization-induced charge density, n-AlGaN doping level and the Schottky barrier height on the positions of the two slopes in the C-V curves are much different from each other. The polarization-induced charge density can be extracted accurately by fitting the experimental C-V curves. It is extracted to be 6.78 x 1012cm-2in modulation-doped Al0.22Ga0.78N/GaN heterostructures with the Al0.22Ga0.78N thickness of 30 nm or 45 nm. The charge density reducesto 1.30 x 1012cm-2in the heterostructure with the Al0.22Ga0.78N thickness of 75 nm. It is thought that the reduction of the polarization-induced charges at the heterointerface is due to the partial relaxation of the Al0.22Ga0.78N layer on GaN.
TEM assessment of GaN/AlGaN/TiAlTiAu and GaN/AlGaN/TiAlPdAu ohmic contacts
Authors: Fay M W , Moldovan G , Harrison I , Birbeck J C , Hughes B T , Uren M J , Martin T , Brown P D 
Published: April 2011

AbstractTiAlTiAu and TiAlPdAu contacts to GaN/AlGaN, rapid thermal annealed at temperatures ranging from 650°C to 950°C, have been investigated using conventional and chemical TEM analysis. Ohmic behaviour was seen for TiAlTiAu contacts annealed at 750°C or higher, but was not observed in TiAlPdAu contacts annealed at up to 950°C. The effect of annealing temperature on the structural evolution of the contact is explained in terms of different extents of interfacial reaction. In particular, the formation of TiN after anneals at high temperatures is required to activate the contact. At anneals of 950°C, TiAlTiAu samples show a structure of TiN grains within an interfacial band, with TiN inclusions into the AlGaN preceded by an Al-Au diffusion front. Inclusion formation and the effect on the contact electrical performance is described.
Novel Sensor Applications of group-III nitrides
Authors: Eickhoff M. , Ambacher O. , Steinhoff G. , Schalwig J. , Neuberger R. , Palacios T. , Monroy E. , Calle F. , Müller G. , Stutzmann M. 
Published: April 2011

AbstractThe present paper gives an overview over different sensor applications of GaN thin films and AlGaN/GaN heterostructures. The response of Pt-GaN Schottky diodes towards hydrogen and hydrogen containing gases is analysed and their gas sensitivity is characterized from room temperature up to 600°C. In addition, the sheet carrier density of a two dimensional electron gas confined at the heterointerface in AlGaN/GaN high electron mobility transistors (HEMTs) is shown to be significantly influenced by changes in the electronic properties of the device surface. This effect is successfully exploited for the realization of ion detectors and sensors for fluid monitoring based on AlGaN/GaN HEMTs with non-metalized gate areas. Promising possibilities of fabricating monolithically integrated sensor devices for wireless signal transmission are demonstrated by the realization of SAW devices on epitaxial AlN-films.
Three-Dimensional Modeling of the High Pressure Organometallic Chemical Vapor Deposition of InN using Trimethylindium and Ammonia
Authors: McCall Sonya D. , Bachmann Klaus J. 
Published: April 2011

AbstractA physico-chemical model of the High Pressure Organometallic Chemical Vapor Deposition (HPOMCVD) process that describes three dimensional transport phenomena as well as gas-phase and surface reactions underlying the growth of compound semiconductors is presented. A reduced-order model of the Organometallic Chemical Vapor Deposition of indium nitride (InN) from trimethylindium In(CH3)3 or TMI and ammonia (NH3) at elevated pressures has been developed and tested using the computational fluid dynamics code, CFD-ACE+. The model describes the flow dynamics coupled to chemical reactions and transport in the flow channel of the Compact Hard Shell Reactor, as a function of substrate temperature, total pressure and centerline flow velocity.
Quantitative Defect Analysis of GaN Thick Films by TEM and AFM
Authors: Bhaskara Praveena , Sung Changmo , Bliss David , Suscavage Michael 
Published: April 2011

AbstractEver since the discovery of the astonishing properties of GaN, many research groups have been involved in the processing of the perfect GaN crystal. Iodine Vapor Phase Growth (IVPG) technique was employed to grow GaN epilayer on a MOCVD pre-deposited buffer layer. This new epitaxial system was characterized by TEM, AFM and EFM. A complete AFM study involved the polarity measurements and the etch pit density measurements. For the first time a systematic study was performed of the dislocation density changing as a function of distance from the substrate. TEM performed on the cross-section, as well as the plan view, of the samples showed a remarkable decrease in the dislocations in the current system, compared to the samples that were solely deposited by MOCVD. Advanced analytical methods of polarity and dislocation density measurements have been established to understand the relation between microstructure and electrical properties of the thick film GaN. Electrostatic Force Microscopy has been suggested as a potential tool for obtaining polarity information.
Microstructural characterization of GaN-GaAs alloys grown on (001) GaAs by molecular beam epitaxy
Authors: Kim Hyonju , Andersson T. G. , Södervall U. , Jäger C. , Jäger W. , Albrecht M. , Bösker G. , Stolwijk N. A. 
Published: April 2011

AbstractWe have investigated microstructural properties of GaAs:N and GaN:As layers using transmission electron microscopy. The samples were grown onto (001)-oriented GaAs substrates by RF-plasma assisted molecular beam epitaxy. It has been found that during the GaAs/GaAs:N epitaxial growth the supplied active nitrogen atoms gave rise to nanometer-size GaN crystallites formed in the GaAs matrix. In addition, silicon incorporation showed abnormal behavior at the two interfaces of the thin GaAs:N layer embedded in GaAs. A model is proposed for the formation of GaN crystallites in GaAs during the growth. In the GaN:As growth, the layer exhibited columnar growth, resulting in domains with different crystallographic orientation. With an increase of the film thickness, the zincblende structure changed to the wurtzite phase of GaN. The distribution of arsenic through the layer thickness was found to be inhomogeneous and be much higher near the GaN/GaAs interface compared to the region near the surface.
Characterization Of G-R Noise In GaN Films Grown By RF-MBE On Intermediate-Temperature Buffer Layers
Authors: Fong W.K. , Leung B.H. , Zhu C.F. , Surya Charles 
Published: April 2011

AbstractWe report detailed investigations of generation-recombination (G-R) noise in GaN films grown by rf-plasma assisted molecular beam epitaxy on intermediate-temperature buffer layer (ITBL) in addition to conventional low-temperature buffer layer. To characterize the film quality affected by the use of ITBL, low-frequency noise measurements were performed. The voltage noise power spectra show a strong dependence on the thickness of the ITBL. A model has been presented to explain the observed G-R noise, which stipulates that the phenomenon arises from the thermally activated trapping and detrapping of carriers by traps. The process leads to the correlated fluctuations in both the carrier number and the coulombic scattering rate. Detailed numerical evaluation shows that number fluctuation dominates in our samples. The calculated trap densities show that the use of ITBL can effectively reduce defect density by over an order of magnitude.
Two Step Growth of InN Films on Sapphire (0001) Substrates Without Nitridation Process by RF-MBE
Authors: Yamaguchi Tomohiro , Saito Yoshiki , Kano Kenji , Muramatsu Tomo , Araki Tsutomu , Nanishi Yasushi , Teraguchi Nobuaki , Suzuki Akira 
Published: April 2011

AbstractInN films were grown on sapphire (0001) substrates by radio-frequency plasma-assisted molecular beam epitaxy. The InN buffer layers deposited at low temperature were either grown on a substrate with nitridation or on a substrate without nitridation. The InN buffer layers on the nitridated substrates were always single crystalline, whereas the buffer layers on non-nitridated substrates were always polycrystalline. However, even without nitridation process, single crystalline InN films could be grown on the polycrystalline InN buffer layers; in this case, the orientation was always [1120] InN//[1120] sapphire epitaxy, which differed from the [1010] InN//[1120] sapphire epitaxy in films grown with nitridation.
Investigation of the Optimum Growth Conditions of Wide-Bandgap Quaternary InAlGaN for UV-LEDs
Authors: Yamabi T. , Kinoshita A. , Hirayama H. , Ainoya M. , Hirata A. , Araki T. , Nanishi Y. , Aoyagi Y. 
Published: April 2011

AbstractWe systematically investigated the optimum growth condition of wide-bandgap quaternary InAlGaN for ultraviolet (UV) light-emitting diodes (LEDs) grown on SiC by metal organic vapor phase epitaxy (MOVPE). We obtained intense UV emission in the wavelength of 315-370 nm from quaternary InAlGaN, which was as high as blue emission from InGaN. We found that the optimized growth temperature of quaternary InAlGaN is shifted from 790 to 870 °C as the emission peak wavelength is changed from 370-315 nm. The strongest PL was obtained with the wavelength around 330 nm. The growth condition for intense PL is found to be decided by two factors, i.e., the carrier confinement in In segregation region and crystalline quality. We also found that the small In mole fraction of 2-5 % is enough to obtain maximally PL intensity for InAlGaN, which is much smaller value than that for InGaN, due to the large carrier confinement with small In fluctuation.
Composition Control during Growth of AlGaN Cladding Layers for InGaN-MQW Lasers with Ridge Formed by Selective Re-growth (RiS-type Lasers)
Authors: Kimura Akitaka , Kuramoto Masaru , Yamaguchi A. Atsushi 
Published: April 2011

AbstractWe investigated the mask-pattern and trimethylalminium (TMAl)-flow-rate dependence of the Al composition in AlGaN selective growth for novel InGaN multiple quantum well lasers having selectively grown ridge structures (RiS-type lasers). The Al composition decreased with increases of the local coverage ratio. This result was explained quantitatively by a simple model in which the Al is deposited as polycrystals on the mask without migration occurring and the Ga is concentrated into the window. Under a high TMAl flow-rate condition, this effect of lowering the Al composition was weakened by the high Ga consumption on the mask, and an desirable Al composition for GaN-based lasers was realized. The model can be used to control the composition of p-AlGaN layers for RiS-type lasers.
Characterization of AlxGa1-xN/ AlyGa1-yN Distributed Bragg Reflectors Grown by Plasma Assisted Molecular Beam Epitaxy
Authors: Klausing H. , Fedler F. , Rotter T. , Mistele D. , Semchinova O. , Stemmer J. , Aderhold J. , Graul J. 
Published: April 2011

AbstractAlxGa1-xN/ AlyGa1-yN Distributed Bragg Reflectors (DBRs) with up to 45 periods have been grown on (0001) sapphire substrates by r.f. plasma-assisted molecular beam epitaxy (PAMBE) with the aid of two Al effusion cells. Several samples were grown with an Al mole fraction varying between 0.38 ≤ x ≤ 1 (0 ≤ y ≤ 0.4) at temperatures of up to 890°C. In all samples, an AlxGa1-xN buffer layer was used to prevent cracking of the quarter wave stack and improving surface morphology by choosing the Al content so that strain energy in the DBR structure would be compensated.X-ray diffraction (XRD) and scanning electron microscopy (SEM) investigations were performed to determine the thickness of the quarter wave layer periods and the Al mole fraction of corresponding AlxGa1-xN single layers.Room-temperature calibrated reflection and transmission (R&T) measurements were performed. Thus stray and self-absorption of the DBRs were extracted from reflectance and transmittance. The thickness of the quarter wave layers was designed such that the measured peak reflectances appeared between 346 nm to 421 nm. The dispersion data, including refractive indices and absorption coefficients, used in the calculation were extracted from R&T measurements done on the above mentioned AlxGa1-xN single layers.