bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth of Oriented Gallium Nitride Films on Amorphous Substrates by Self Assembly
Authors: Li Hongwei , Sunkara Mahendra K. 
Published: April 2011

ABSTRACTC-plane oriented thin films of gallium nitride (GaN) were grown on both amorphous quartz substrates and single crystalline c-sapphire substrates at sub-atmospheric pressures by exposing molten gallium thin films to electron cyclotron resonance (ECR) microwave generated nitrogen plasma. Gallium nitride crystals nucleated from molten gallium and self-aligned with respect to each other due to the mobility of nitrogenated gallium and formed textured film directly on amorphous substrates. Scanning electron microscopy (SEM) images and X-ray Diffraction (XRD) spectra confirmed the orientation among crystals. Micro-Raman spectra exhibited a FWHM of 3 cm−1. Self-assembled, nanocrystalline GaN thin films were obtained when spin-coated gallium thin films (< 1 μm) on quartz substrates were nitrided.
Raman Mapping and Finite Element Analysis of Epitaxial Lateral Overgrown GaN on Sapphire Substrates
Authors: Benyoucef M. , Kuball M. , Beaumont B. , Bousquet V. , Gibart P. 
Published: April 2011

ABSTRACTUsing micro-Raman scattering and finite element (FE) analysis, stress fields in epitaxial lateral overgrown (ELO) GaN fabricated by metalorganic vapor phase epitaxy (MOVPE) on sapphire substrates using a two-step growth method were investigated. Nearly full stress relaxation at the top ELO GaN surface can be achieved by increasing the thickness of ELO GaN to about 50 μm. Reductions in stress variation between window and overgrown regions can be achieved by using a double ELO GaN growth at a much smaller ELO thickness. Increased compressive stress at the coalescence boundary of two adjacent wings of ELO GaN was related to the presence of voids in this area. In the double ELO growth, stress near the top surface was mainly attributed to the presence of voids on top of the upper dielectric mask.
Single Crystalline InN Films Grown on Si Substrates By Using A Brief Substrate Nitridation Process
Authors: Yamaguchi Tomohiro , Mizuo Kazuhiro , Saito Yoshiki , Noguchi Takuma , Araki Tsutomu , Nanishi Yasushi , Miyajima Takao , Kudo Yoshihiro 
Published: April 2011

ABSTRACTInN films were grown on Si (111) substrates by radio-frequency plasma-excited molecular beam epitaxy. InN films highly oriented to the c-axis were obtained by optimizing growth conditions in the direct growth on Si. Growth of single crystalline InN films was realized on Si substrates with substrate nitridation for 3 min. On the other hands, when the substrate nitridation was lasted over 30 min, obtained InN films were polycrystalline due to the amorphous SiNx layer formed on a substrate surface. We also studied the local atomic structure in the single crystalline InN film using extended X-ray absorption fine structure measurements.
The Influence of Substrate Surface Polarity on Optical Properties of GaN Grown on Single Crystal Bulk AlN
Authors: Tamulaitis G. , Yilmaz I. , Shur M. S. , Gaska R. , Chen C. , Yang J. , Kuokstis E. , Khan A. , Rojo J. C. , Schowalter L. J. 
Published: April 2011

ABSTRACTPhotoluminescence of the GaN layers grown both on N-face and Al-face bulk AlN is studied under CW and pulsed laser excitation in the temperature range from 8 K to 300 K. We compare localization of excitons, residual strain, and activation energies for thermally activated transfer of carriers to nonradiative recombination. At high excitation intensities, conditions for carrier heating, which is important for the threshold of stimulated emission, are also investigated.
Optical Characterization of Bulk GaN Grown from a Na/Ga Flux
Authors: Palle K. , Chen L. , Liu H. X. , Skromme B. J. , Yamane H. , Aoki M. , Hoffman C. B. , DiSalvo F. J. 
Published: April 2011

ABSTRACTBulk GaN crystals up to several mm in size, grown by a Na/Ga flux method, have been characterized using room and low temperature photoluminescence (PL) and panchromatic cathodoluminescence (CL) imaging. Highly resolved excitonic PL spectra are obtained for material grown in a new, large-scale reactor. The crystal polarity affects the incorporation of residual Zn and Mg or Si acceptors and the deep level luminescence bands in c-oriented platelets. A Zn (A°,X) triplet structure with unusual thermalization properties and a highly resolved structural defect related PL peak are observed. Striations are found in some of the smaller platelets by CL imaging, but are absent in the prismatic crystals.
Electroreflectance and Photoreflectance Studies of Electric Fields in Pt/GaN Schottky Diodes and AlGaN/GaN Heterostructures
Authors: Shokhovets S. , Goldhahn R. , Gobsch G. , Ambacher O. , Smorchkova I. P. , Speck J. S. , Mishra U. , Link A. , Hermann M. , Eickhoff M. 
Published: April 2011

ABSTRACTWe have performed electroreflectance and photoreflectance studies of Pt/GaN Schottky diodes with Ga- and N-face polarity as well as AlGaN/GaN based transistor heterostructures. The experimental data were analyzed using electric field-dependent dielectric functions of GaN and AlGaN. Inhomogeneities in the electric fields were taken into account by application of a multi-layer formalism. We observed an increase of the electric field strength underneath the Schottky contact and in the AlGaN barrier with increasing temperature. The results are explained in terms of temperature dependent densities of ionized impurities and surface charges.
Effect of Oxygen Pressure on Magnesium Oxide Dielectrics Grown on Gan by Plasma Assisted Gas Source Molecular Beam Epitaxy
Authors: Onstine A. H. , Gila B. P. , Kim J. , Stodilka D. , Allums K. , Abernathy C. R. , Ren F. , Pearton S. J. 
Published: April 2011

ABSTRACTThe effect of oxygen pressure on MgO grown by RF plasma assisted gas-source molecular beam epitaxy was investigated. Increasing oxygen pressure was found to decrease the growth rate, improve the morphology and reduce the Mg/O ratio to near that obtained from bulk single crystal MgO. By contrast, the electrical characteristics of MgO/GaN diodes showed continual improvement in breakdown field and interface state density as the pressure was decreased. The lowest pressure tested, 1×10−5Torr, produced the lowest Dit, 3×1011 eV−1cm−2, and the highest VBD, 4.4 MV/cm. Cross sectional transmission electron microscopy of the MgO grown at the lowest pressure showed the initial 40 monolayers to be epitaxial, with the remainder of the layer appearing to be fine grained poly-crystal. Comparisons with films grown using an electron cyclotron resonance (ECR) plasma suggest that higher ion energies are desirable for obtaining the best electrical characteristics.
High-Mobility Ga-Polarity GaN achieved by NH3-MBE
Authors: Wang J. X. , Wang X. L. , Sun D. Z. , Li J. M. , Zeng Y. P. , Hu G. X. , Liu H. X. , Lin L. Y. 
Published: April 2011

ABSTRACTGaN epilayers were grown on (0001) sapphire substrates by NH3-MBE and RF-MBE (radio frequency plasma). The polarities of the epilayers were investigated by in-situ RHEED, chemical solution etching and AFM surface examination. By using a RF-MBE grown GaN layer as template to deposit GaN epilayer by NH3-MBE method, we found that not only Ga-polarity GaN films were repeatedly obtained, but also the electron mobility of these Ga-polarity films was significantly improved with a best value of 290 cm2/V.s at room temperature. Experimental results show it is an easy and stable way for growth of high quality Ga-polarity GaN films.
Growth of Quaternary AlInGaN/GaN Heterostructures by Plasma Assisted MBE
Authors: Monroy E. , Gogneau N. , Jalabert D. , Enjalbert F. , Bellet-Amalnc E. , Hon Y. , Dang Le Si , Daudin B. 
Published: April 2011

ABSTRACTEpitaxial growth of quaternary AlGalnN compounds by plasma-assisted molecular beam epitaxy has been demonstrated. Two-dimensional growth is achieved under In excess, with a monolayer of In segregating at the growth front. The maximum In incorporation is significantly affected by the substrate temperature and the Al mole fraction of the alloy. This behavior has been attributed to the enhancement of In segregation due to the high binding energy of A1N compared to InN and GaN.
Deep Donor-Acceptor Pair Luminescence in Codoped GaN
Authors: Han Bing , Gregie Joel M. , Ulmer Melville P. , Wessels Bruce W. 
Published: April 2011

ABSTRACTDeep level defects formed in p-type GaN:Mg codoped with shallow donors have been investigated by photoluminescence (PL) spectroscopy. A donor-acceptor pair (DAP) luminescence band peaked at 2.45 eV dominates the room temperature PL spectrum in heavily codoped epilayers. A superlinear dependence of PL intensity on excitation density is observed for this band, with an exponent of 1.4∼1.7. The intensity of this band increases with increasing temperature with a maximum at 264K. To explain the luminescent behavior a DAP model was developed whereby the recombination involves a deep donor and shallow Mg acceptor. The deep donor is tentatively attributed to a DX center.
Deposition of GaN Films on Glass Substrate and Its Application to UV Electroluminescent Devices
Authors: Honda Tohru , Iga Kenichi , Kawanishi Hideo , Sakaguchi Takahiro , Koyama Fumio 
Published: April 2011

AbstractGaN films were deposited on glass substrates using a compound-source molecular beam epitaxy technique. Electroluminescent devices with a double-insulator structure were also fabricated using the deposited films. When the devices were operated using a sine-wave voltage, one of the emission peaks was located in the UV spectral region. Introducing a small ammonia flow increased the deposition rate.
Crack Nucleation in AlGaN/GaN Heterostructures
Authors: Parbrook Peter J. , Whitehead Malcolm A. , Lynch Richard J. , Murray Robert T. 
Published: April 2011

ABSTRACTThe tensile strain in AlGaN layers on GaN is well established to lead to cracking if a critical thickness is reached, unless measures such as interlayers are applied to prevent their formation. However in devices, such as HFETs such an approach is impractical. Growth of AlGaN-GaN structures was carried out by MOVPE using a standard two stage process for the growth of the GaN on sapphire. The crack structures were examined by optical and atomic force microscopy. Studies on thin AlGaN layers on GaN close to the crack critical thickness show the stress centres from which the cracks propagate are threading dislocations with cracks often initially forming to link together these stress centres if they are in close proximity. These cracks then extend and “lock” into the generally observed 〈2110〉 direction in more highly strained layers. A macroscopically uniform crack array is observed in these thin AlGaN samples.
Micro-Raman Spectroscopy: Self-Heating Effects In Deep UV Light Emitting Diodes
Authors: Sarua A. , Kuball M. , Uren M. J. , Chitnis A. , Zhang J. P. , Adivarahan V. , Shatalov M. , Asif Khan M. 
Published: April 2011

ABSTRACTUltraviolet light emitting diodes (LED) based on GaN and its ternary alloy AlGaN are key devices for applications such as solid state white lighting and chemical sensing. Ultraviolet LEDs are prone to self-heating effects, i.e., temperature rises during operation, contributing significantly to the commonly observed saturation of light output power at relatively low input currents. Rather little, however, is known about the actual device temperature of an operating ultraviolet LED. Using micro-Raman spectroscopy temperature measurements were performed as a function of input current on 325nm-Al0.18Ga0.82N/Al0.12Ga0.88N multiple quantum wells LEDs grown on sapphire substrates, flip-chip mounted on SiC for heat-sinking. Temperature maps were recorded over the active device area. Temperature rises of about 65 °C were measured at input currents as low as 50mA (at 8V) for 200 μm x 200 μm size LEDs despite flipchip mounting the devices. Temperature rises at the device edges were found to be higher than in the device center, due to combined heat sinking and current crowding effects. Finite difference heat dissipation simulations were performed and compared to the experimental results.
Formation of quantum dots by self-rearrangement of metastable 2D GaN
Authors: Gogneau N. , Jalabert D. , Monroy E. , Adelmann C. , Daudin. B. 
Published: April 2011

ABSTRACTWe propose a new procedure to grow GaN quantum dots (QDs) on AlN by using the Ga surfactant effect in plasma-assisted molecular beam epitaxy. Self-formed GaN islands were spontaneously generated under vacuum from a GaN 2D layer grown under Ga-rich conditions. Island characteristics (size and density) are studied as a function of the GaN coverage. We demonstrate that the QD density can be controlled in the 1010 cm−2 to 2 × 1011 cm−2 range. It is shown that beyond a given GaN thickness there is a coexistence between elastic and plastic relaxation.
Gate Current Modeling for Insulating Gate III-N Heterostructure Field-Effect Transistors
Authors: Clarke Frederick W. , Ho Fat Duen , Asif Khan M. , Simin Grigory , Yang J. , Gaska Remis , Shur Michael S. , Deng Jianyu , Karmalkar S. 
Published: April 2011

AbstractGate current plays an important role in determining the characteristics and limiting performance of GaN-based field effect transistors. In GaN-based HFETs, the gate current limits the gate voltage swing and, hence, the maximum device current. Since the electron transport across the wide band gap barrier layer involves trapping, under certain bias conditions, the gate current leads to the threshold voltage shifts and causes reliability problems. Under reverse bias, the gate leakage in GaN-based HFET dominates the minimum (pinch-off) drain current. Insulating gate HFETs (i.e. Metal Oxide Heterostructure Field Effect Transistors – MOSHFETs) have the gate leakage currents 4 – 6 orders of magnitude lower than HFETs, even at elevated temperatures up to 300 °C. In this paper, we report on the gate current characteristics in these devices at room and elevated temperatures. We propose a semi-empirical model for the current-voltage characteristics in these devices, which is in good agreement with experimental data. Our data also show that both tunneling and temperature activation are important factors in MOSHFETs. These results are important for possible applications of GaN MOSHFETs in high power amplifiers and power switches as well as in non-volatile memory devices and integrated circuits that will operate in a much wider temperature range than conventional silicon and GaAs devices.
High-Quality AlGaN/GaN HFET Structures Grown by MOCVD Using Intermediate High Temperature AlGaN/GaN Superlattices
Authors: Demchuk Alexander , Olson Don , Shin Minseub , Olson Dan , Nussbaum Peter , Strom Andy , Bates Simon , Hofmann Frank , Munns Gordon 
Published: April 2011

ABSTRACTWe report on device quality Al0.28Ga0.72N/GaN heterostructures growth by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) using intermediate AlxGa1-xN/GaN superlattices (SL) with x<0.15. High-quality Al0.28Ga0.72N/GaN heterostructures have been confirmed with HRXRD analysis by measurement of mosaic twist and tilt in growth films, SEM with selective etching and Van der Pauw Hall measurements. The edge and threading dislocations were efficiently filtered by the AlGaN/GaN SL resulting in further reduction dislocation densities at the channel. Additionally, the superlattice served to improve the planarity of the channel heterointerface as evidenced by x-ray and AFM analysis. The increase of 2-DEG mobility from ∼1187 cm2/V s to ∼1443 cm2/V s was obtained at the carrier density of 1.0 to 1.2×1013 cm−2 on heterostructures with intermediate AlGaN/GaN SL grown on sapphire.
Thermal Stability of High k Layers
Authors: Zhao C. , Cosnier V. , Chen P. J. , Richard O. , Roebben G. , Maes J. , Van Elshocht S. , Bender H. , Young E , Van Der Biest O. , Caymax M. , Vandervorst W. , De Gendt S. , Heyns M. 
Published: April 2011

ABSTRACTThermal stability of amorphous phases in various high-k layers (Al2O3, ZrO2, HfO2, ZrAlOx, HfAlOx and HfSiOx) and the phase transformation of crystalline ZrO2 and HfO2 were studied experimentally, as functions of surface preparation, deposition conditions, material composition and post deposition thermal treatment. It is found that pure ZrO2 and HfO2 show relatively low crystallization onset temperatures. The crystalline ZrO2 or HfO2 phases are tetragonal or monoclinic, depending on the layer thickness. The phase transformation of metastable t-phase into stable m-phase has been observed in ZrO2 and HfO2. Crystallization behavior of Al2O3 depends on the surface preparation of the substrate. ALCVD grown Al2O3 layers on an oxide-based surface remain amorphous after 1100°C spike annealing, while those on HF-last surface crystallize at temperatures around 800°C. Alloying Al2O3 into ZrO2 and HfO2 can improve their resistance to crystallization under thermal exposure. The kinetics of the crystallization in the alloys can be described by linear TTT curves. Hf-aluminates show better thermal stability than Zr-aluminates. A defect model relative to the phase transformation is discussed, based on the above observations.
Screening the High-k Layer Quality by Means of Open Circuit Potential Analysis and Wet Chemical Etching
Authors: Claes Martine , De Gendt Stefan , Witters Thomas , Kaushik Vidya , Chen Jerry , Conard Thierry , Delabie Annelies , Van Elshocht Sven , Heyns Marc 
Published: April 2011

ABSTRACTA fast way to monitor the quality of high-k dielectric layers is wet etching, either monitored by Open Circuit Potential analysis or by Scanning Electron Microscopy. Defect densities in the order of 1.109 defects/cm2 are observed for as-deposited HfO2 layers. It is assumed that the mechanism for wet chemical defect observation is either due to crystallization and/or due to an oxygen deficient HfO2 layer resulting in Si/SiO up-diffusion upon thermal treatment. However, after appropriate post deposition annealing wet etch defect free layers can be prepared.
X-ray absorption studies of high performance Low-k dielectric materials
Authors: Yoda T. , Miyajima H. , Shimada M. , Nakata R. , Hashimoto H. 
Published: April 2011

ABSTRACTThe XAFS measurement of the MSQ type low-k dielectrics (LKD™) was conducted to clarify the structure change with and without the EB cure. Furthermore, three different types of other MSQ films, the ladder structure, the random structure and the CVD film, have been investigated as references. We have determined Si-O-Si bond angle and Si-O(Si-C) bond length by fitting the Fourier transformed EXAFS spectra.The ladder structure and the random structure have Si-O-Si bond angle of 133 and 146, respectively.Si-O-Si bond angle of LKD™ film is among that of the ladder and the random structure, and the XANES spectrum of LKD™ film displays two broad features, corresponding to the mixture of both structures. In contrast, Si-O-Si angles of the EB cured LKD™ film and the CVD film resemble each other, and the XANES features of both films are almost identical with that of the random structure.We have confirmed that the EB cure process for LKD™ film makes drastic structure change from the mixture of ladder and random structure to the random network structure.
A Selective Etching Process for Chemically Inert High-k Metal Oxides
Authors: Saenger Katherine L. , Okorn-Schmidt Harald F. , D'Emic Christopher P. 
Published: April 2011

ABSTRACTOnce annealed, high-k metal oxides such as HfO2 and Al2O3 can be extremely difficult to etch by wet chemical methods. Here we describe how ion bombardment at relatively low energy (a few hundred eV) can be used to make exposed regions of annealed HfO2 films etchable in aqueous HF-based solutions. HfO2 layers, 2–5 nm in thickness, were deposited by atomic layer chemical vapor deposition (ALCVD) on Si substrates, annealed at 700 °C, and subjected to selected-area ion bombardment supplied by an oxygen plasma in a reactive ion etching tool. Etch times (as indicated by time to “dewet“) were examined as a function of HfO2 thickness, the power and time of oxygen plasma treatments, post-oxygen-plasma anneals, and wet etch chemistry. Strategies for etching thicker films and additional data provided by electrochemical open circuit potential (OCP) measurements will also be discussed.
Phase Formation in Ti (Ta)-Ni and Co-Ti Films Deposited on (001)Si in N2 Atmospheres.
Authors: Vasiliev A. L. , Aindow M. , Vasiliev A. G. , Horin I. A. , Orlikovsky A. A. 
Published: April 2011

ABSTRACTA series of electron microscopy investigations on the microstructure produced by surface-diffusion reactions between Si substrates heated to 700–800°C and Ti-Co, Ti-Ni or Ta-Ni alloys deposited in a nitrogen ambient with and without barrier layers are described. The TEM data show clear phase separation into TaSi2 and NiSi2 for the Ta-Ni film deposited in a high N2 pressure ambient. Deposition at lower N2 pressure led to the formation of a mixed Ni-Ta-Si layer. The phase separation effect was also absent for Ni-Ti films even at high N2 pressure. The presence of barrier layers strongly affected the surface diffusion reactions in the Co-Ti-Si system. Formation of Ti-(O) or CoSix amorphous layers at the Si surface prevented the interdiffusion of Si and Co, such that even pure Co or Co2Si layers could be formed.
Kinetics of agglomeration of NiSi and NiSi2 phase formation.
Authors: Detavernier C. , Özcan A. , Lavoie C. , Sweet Jean-Jordan , Harper J. M. E. 
Published: April 2011

ABSTRACTWe have studied the kinetics of NiSi agglomeration and NiSi2 phase formation during heating of NiSi on Si, using simultaneous in situ measurements of resistance, light scattering and x-ray diffraction. NiSi is a desirable contact to Si because of its low resistivity, limited Si consumption and low formation temperature. However, the formation of the higher resistivity phase NiSi2 must be avoided for device applications. Ni thin films 5 to 30 nm thick were deposited on substrates of poly-Si and silicon-on-insulator (SOI) and were studied using heating rates from 0.3 to 27 °C/s. At low heating rates and for the thinnest films studied, NiSi agglomeration precedes NiSi2 nucleation by as much as 350°C. The agglomeration temperature decreases with decreasing film thickness and linewidth. Once the film is agglomerated, the formation of NiSi2 is delayed to higher temperature by its low nucleation site density and decreased contact area. We conclude that agglomeration is the primary failure mechanism limiting the morphological stability of NiSi as a contact material to Si devices.
Formation of Ni mono-germanosilicide on heavily B-doped epitaxial SiGe for ultra-shallow source/drain contacts
Authors: Isheden Christian , Seger Johan , Radamson Henry H. , Zhang Shi-Li , Östling Mikael 
Published: April 2011

ABSTRACTThe formation of Ni germanosilicides during solid-state interaction between Ni and heavily B-doped strained epitaxial Si1-xGex films with x=0.18, 0.32 and 0.37 is studied. No NiSi2 is found in these samples even after annealing at 850 °C, which can be compared to the formation of NiSi2 at 750 °C on Si(100). Resistance and diffraction studies for the Si0.82Ge0.18 sample indicate that NiSi0.82Ge0.18 forms and the NiSi0.82Ge0.18/Si0.82Ge0.18 structure is stable from 400 to 700 °C. For the NiSi1-uGeu formed in all Si1-xGex samples, where u can be different from x, a strong film texturing is observed. When the Ge fraction is increased from 18 at.% to 32–37 at.%, the morphological stability of the film is degraded and a substantial increase in sheet resistance occurs already at 600 °C. The contact resistivity for the NiSi0.8Ge0.2/Si0.8Ge0.2 interface formed at 550 °C is determined as 1.2×10-7 Ωcm2, which satisfies the RS contact resistivity requirement for the 70 nm technology node.