bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Temperature Illumination-Induced Metastability in Undoped Semi-Insulating GaN Grown by Metalorganic Vapor Phase Epitaxy
Authors: Fang Z-Q. , Claflin B. B. , Look D. C. , Myers T. H. , Koleske D. D. , Wickenden A. E. , Henry R. L. 
Published: April 2011

ABSTRACTHigh-temperature (high-T) illumination-induced metastability in undoped semi-insulating (SI) GaN grown on a-plane sapphire by metalorganic vapor phase epitaxy has been studied using thermally stimulated current (TSC) spectroscopy, photocurrent (PC) and persistent photocurrent (PPC) measurements. The metastability can be induced by illumination at 390>T>300K (using either white or 360-nm light), followed by cooling the sample to 83 K in the dark. Without high-T illumination, the SI-GaN sample stays in its normal state (“off” state), and shows at least six TSC traps, B (0.63 eV), Bx (0.51 eV), C1 (0.44 eV), C (0.32 eV), D (0.23 eV), and E (0.16 eV). However, after high-T illumination the sample goes into a metastable state (“on” state), and shows a strong increase in both the PC at 83 K and the TSC of traps D, C, and E, accompanied by significant change in their relative densities. PPC at 83 K in the “on” state lasts much longer than that in the “off” state. Association of possible point defects and dislocations with the metastability behavior will be discussed.
AlGaN/GaN HFETs for Automotive Applications
Authors: Birkhahn Ronald , Gotthold David , Cauffman Nathan , Peres Boris , Yoshida Seikoh 
Published: April 2011

ABSTRACTAlGaN/GaN heterojunction field effect transistors (HFET) on sapphire substrates have demonstrated ability as power devices operating with high current densities and high breakdown voltages. Additionally, AlGaN/GaN HFET devices have a very low on-state resistance. This makes these devices ideal for automotive applications such as switching relays, DC-DC converters, and power inverters. By 2006, switching devices using GaN-based FETs are anticipated to be employed in luxury automobiles and transitioned to the mass market by 2009.In this presentation, data from AlGaN/GaN HFET's grown in an Emcore D180 MOCVD system will be presented. Typical production-scale material results (on 2” sapphire substrates) for these wafers were: μ ∼ 1000 cm2/Vs, Ns = 1.0×1013 cm−2, and Rs ∼ 450 Ω/square with <3% variation across the wafer. These wafers were then processed into devices using Pt/Au gate contacts with 2 μm gate length, 200 μm gate width, and a source to drain spacing of 13 μm. A total of 1000 FETs were combined in parallel for an effective gate width of 20 cm for high current operation (10A). These devices have a lower on-state resistance (<0.01 Ω-cm2) and higher Schottky breakdown voltages (400 V) than the theoretical limit of Si MOSFET devices. These devices demonstrate suitability for insertion in automotive electrical harnesses.
Ti/Al- GaN Reaction Mechanism Forming Low Contact Resistivity
Authors: Fukasawa Yoshimichi , Nakamura Tomonori , Nakamura Tohru 
Published: April 2011

ABSTRACTThe mechanism of Ti/Al reaction to n-GaN was studied to form ohmic contacts with low contact resistivity. N-GaN layers with a carrier concentration of 2.17×1018cm−3were deposited on sapphire substrates. Ti/Al metals were deposited by conventional electron-beam techniques. Contact resistivity decreased as the Ti thickness increased, and increased as the Al thickness increased. The lowest contact resistivity was measured at 1.20 × 10−6Ωcm2for 80 nm Ti /100 nm Al. After annealing at 900 °C, Al/AlTi/TiN layers on GaN were formed and Al Ti alloy thickness decreased as Ti thickness increased, from 1.5 MeV Rutherford Backscattering Spectroscopy(RBS) measurement. It was found that the contact resistivity was reduced as alloy metal thickness into GaN was increased.
Effect of growth temperature on the microstructure of the nucleation layers of GaN grown by MOCVD on (1120) sapphire
Authors: Wojtowicz T. , Ruterana P. , Twigg M. E. , Henry R. L. , Koleske D. D. , Wickenden A. E. 
Published: April 2011

AbstractMost of the work done on GaN has taken into account layers grown on the (0001) sapphire plane. However one would expect the growth on the (1120) plane to lead to different structural defects. As has been shown, in one direction, the mismatch is rather small. In this work, we have carried out structural analysis of nucleation layers grown at temperatures ranging from 600°C to 1100°C. It is shown that for many of the structural parameters, such as the orientation relationships, the layer morphology and the nucleation mechanism critically depend on the growth temperature. At the lowest temperatures, the growth is completely three dimensional with a mixture of the two traditional orientation relationships, but the coalescence thickness is small. In a next step, the A orientation relationship predominates and the layer roughness tends to slightly decrease. This orientation is never perfect, and there is always 1.5° misorientation to the same direction in sapphire, whereas the B orientation is always perfect. At an intermediate temperature, island growth is predominant, whereas towards the high temperature end the B orientation becomes predominant. For the highest growth temperatures, the nucleated layers are completely flat and with the B orientation, although they contain a quite large number of defects such as inversion domains.
Electrical Properties of GaN/Si Grown by MOCVD
Authors: Yoshida Seikoh , Li Jiang , Wada Takahiro , Takehara Hironari 
Published: April 2011

ABSTRACTGaN growth on Si substrate is very attractive for realizing low cost electronic devices. We grew a thin GaN film on p-type Si(111) substrate using AlGaN high temperature buffer without using a conventional low temperature buffer. A homogeneous buffer layer was obtained at 1093 K and a homogenous 500 nm thick GaN layer was also obtained without any crack. Using a transmission electron microscopy (TEM), we observed that the cross-section of GaN and AlGaN buffer was very smooth and also the surface of GaN was flat although the threading dislocations were observed. Furthermore, we directly fabricated a metal semiconductor field effect transistor (MESFET) using a 500 nm-thick GaN/Si without any high resistive GaN layer. A Schottky electrode was Pt/Au and an ohmic electrode was Al/Ti/Au. A Schottky breakdown voltage was over 100 V. Also, we confirmed a high temperature operation of the MESFET using a thin GaN film on Si substrate at 573 K.
Studies on Epitaxial Relationship and Interface Structure of AlN/Si(111) and GaN/Si(111) Heterostructures
Authors: Rawdanowicz T. A. , Wang H. , Kvit A. , Narayan J. 
Published: April 2011

ABSTRACTWe present the details of epitaxial growth interface structure of single wurtzite AlN thin films on (111) Si substrates by laser-molecular-beam-epitaxy. High quality AlN thin films with atomically sharp interfaces can be obtained by Laser-MBE at a substrate temperature of 650 ±10°C. X-ray diffraction and high resolution transmission electron microscopy was used to study the details of epitaxial growth of AlN on Si(111) substrate. The orientation-relationship of AlN on Si(111) was studied from Si <110> and <112> zone axis and determined to be AlN [2110]|Si[110] and AlN [0110]|Si[211]. The atomic structure of the interface was studied by high-resolution transmission electron microscopy and Fourier filtered image of cross-sectional AlN/Si(111) samples from both Si<110> and <112> zone axis. The results revealed the domain matching epitaxy of 4:5 ratio between the interplanar distances of Si(110) and AlN [2110]. We also present similarities and differences between the growth mechanism of AlN/Si(111) and GaN/Si(111) heterostructures.
Experimental and Theoretical Analysis of Heat and Mass Transport in the System for AlN Bulk Crystal Growth
Authors: Bogdanov M. V. , Karpov S. Yu. , Kulik A. V. , Ramm M. S. , Makarov Yu. N. , Schlesser R. , Dalmau R. F. , Sitar Z. 
Published: April 2011

ABSTRACTBulk AlN crystal growth by Physical Vapor Transport (PVT) is studied both experimentally and numerically. This paper presents the analysis of heat and mass transport mechanisms in closed and partially open crucible geometries. The heat transfer in the growth system used at North Carolina State University (NCSU) is simulated. The computed temperature profiles are used in the analysis of mass transport in the growth cell to gain understanding of the effect of species exchange between the crucible and environment on the AlN growth rate. The model predictions are in reasonable agreement with observations.
Production of Sapphire Blanks and Substrates for Blue LEDs and LDs
Authors: Khattak Chandra P. , Schmid Frederick , Guggenheim Paul J. , Smith Maynard B. , Rogers Henry H. , Schmid Kurt 
Published: April 2011

ABSTRACTThe Heat Exchanger Method (HEM) of crystal growing was combined with the Fixed Abrasive Slicing Technology (FAST) to produce low-cost, high-quality sapphire substrates for deposition of the GaN family of compounds. Production quantities of 2-inch diameter blanks have been supplied, and 3-inch diameter material has been qualified. Current technology can be used to prepare sapphire blanks up to 6-inch diameter.
Transport and Chemical Mechanisms in GaN Hydride Vapor Phase Epitaxy
Authors: Karpov Sergey Yu. , Segal Alexander S. , Zimina Darya V. , Smirnov Sergey A. , Sid'ko Alexander P. , Kondratyev Alexey V. , Makarov Yuri N. , Martin Denis , Wagner Volker , Ilegems Marc 
Published: April 2011

ABSTRACTOn the basis of both experimental and theoretical studies, a simple quasi-thermodynamic model of surface kinetics is suggested for Hydride Vapor Phase Epitaxy (HVPE) of GaN, working in a wide range of growth conditions. Coupled with detailed 3D modeling of species transport in a horizontal reactor, the model provides quantitative predictions for the GaN growth rate as a function of process parameters. Significance of transport effects on growth rate uniformity is demonstrated.
Growth of Thick InN by Molecular Beam Epitaxy
Authors: Lu Hai , Schaff William J. , Eastman Lester F. , Wu J. , Walukiewicz Wladek , Look David C. , Molnar Richard J. 
Published: April 2011

ABSTRACTIn this study, InN films with thickness up to 7.5 micron were prepared by molecular beam epitaxy (MBE) on (0001) sapphire and quasi-bulk GaN templates. Previously it has been challenging to grow InN film much beyond 1 micron because the growing surface tended to become rough. Techniques to overcome this limit have been developed. Various buffer techniques were used and compared to optimize the epitaxial growth. It was found that with increasing film thickness, Hall mobility will monotonically increase, while carrier concentration decreases. Hall mobility beyond 2100 cm2/Vs with carrier concentration close to 3×1017 cm−3 was obtained at room temperature. Compared with the lowest carrier concentration ∼2×1018 cm−3 obtained on thin InN films grown at the same condition, the conclusion is that impurities from the growth environment are not responsible for the high background doping of InN. Instead, some structural defects or substrate/buffer impurities may be the major source of the unintentional doping, which can be reduced by growing thicker films.Some results on Mg and Be doping of InN will be reported as well. To date, all Mg and Be doping attempts have resulted in n-type material.
Thermoelectric properties of III-nitrides and III-oxynitrides prepared by reactive rf-sputtering: targetting a thermopower device
Authors: Yamaguchi S. , Iwamura Y. , Yamamoto A. 
Published: April 2011

ABSTRACTWe have studied thermoelectric properties of III-nitrides of Al1-xInxN and III-oxynitrides of Al1-xInxOsNt and InOsNt prepared by radio-frequency sputtering with the aim of fabricating a thermoelectric power device based on III-nitride semiconductors. For Al0.55In0.45N, the maximum value of power factor was 3.63×10−4 W/mK2 at 873K. For Al0.02In0.98O1.14N0.49 and Al0.14In0.86O1.30N0.67, the maximum power factor was 2.82×10−4 W/mK2 and 4.73×10−4 W/mK2 at 873 K, respectively. For InO0.82N0.86, it was 3.75×10−4 W/mK2 at 973 K.
X-Ray Diffraction Analysis of GaN and AlGaN
Authors: Kang H. , Spencer N. , Nicol D. , Feng Z. C. , Ferguson I. , Guo S. P. , Pophristic M. , Peres B. 
Published: April 2011

ABSTRACTIn this paper, threading dislocation densities in GaN and AlGaN epitaxial layers have been evaluated using two different X-ray analysis techniques; a Williamson Hall (WH) plot and reciprocal space mapping (RSM). GaN and AlGaN have crystalline growth composed of columnar structures that can be estimated by coherence length and angular misorientation measured by X-ray. A WH plot can provide information about coherence length and tilt angle from a linear fit to the linewidth of the triple axis rocking curve (000l) symmetric reflections. RSM is typically used to obtain this data, but it is more involved in technique. The two dominant components of threading dislocation densities (screw and edge types) in the GaN and AlGaN epitaxial layers were found to be similar by both techniques. The treading dislocation density correlates to the size of columnar structure as determined by coherence length, tilt angle, and twist angle. The effect of Al composition in AlGaN alloys on these dislocation densities was investigated and found to depend on strongly on the type of nucleation layer, GaN or AlN.
Solar-Blind AlGaN-based Schottky Photodiodes With High Detectivity and Low Noise
Authors: Biyikli Necmi , Aytur Orhan , Kimukin Ibrahim , Tut Turgut , Ozbay Ekmel 
Published: April 2011

AbstractWe report on the design, fabrication and characterization of solar-blind Schottky photodiodes with high detectivity and low noise. The devices were fabricated on n-/n+ AlGaN/GaN hetero-structures using a microwave compatible fabrication process. Using Al0.38Ga0.62N absorption layer, true solar-blind operation with a cutoff wavelength of ∼274 nm was achieved. The solar-blind detectors exhibited < 400 fA dark current in the 0–25 V reverse bias regime, and a maximum responsivity of 89 mA/W around 267 nm. The photovoltaic detectivity of the devices were in excess of 2.6×1012 cmHz1/2/W, and the detector noise was 1/f limited with a noise power density less than 3×10−29 A2/Hz at 10 KHz.
A GaN-free LED Structure for High UV-light Extraction
Authors: Nishida Toshio , Ban Tomoyuki , Kobayashi Naoki 
Published: April 2011

ABSTRACTWe improved the extraction of ultraviolet light from AlGaN-based light emitting diodes (LEDs) at the wavelength of about 350 nm, by introducing a transparent structure that is free from binary GaN. We used an AlN-template layer on a sapphire substrate as starting medium of the metal organic vapor phase epitaxial growth. The buffer layer is an Al0.2Ga00.8N alloy. We also used a short period alloy superlattice as transparent and conductive p-type cladding and p-type contact layers. The resultant epitaxial structure is confirmed to be transparent with the transmittance of about 90% within the wavelength range of 340 – 400 nm. The crystal quality of the Al0.2Ga00.8N buffer layer was estimated by the transmission electron microscope (TEM) observation. The dislocation density of AlGaN buffer layer was highly reduced on the AlN template layer, both of which have a low density of screw and mixed-type dislocations, of the order of 10−8cm−2. We also found that light extraction is improved by a factor of 6 by introducing the transparent LED structure and a p-contact mirror. The resultant LED shows high performance under RT-CW operation, where 1 mW output power at 348 nm with 20 mA injection corresponds to the external quantum efficiency of 1.4 %. The maximum power was 7 mW at 220 mA. The emission spectrum is highly monochromatic with the UV-to-visible intensity ratio of about 1000. We also demonstrate the application of this transparent UV-LED to white light source in a bottom-emission geometry.
Thermal analyses of bulk amorphous oxides and silicates of zirconium and hafnium
Authors: Ushakov S. V. , Brown C. E. , Navrotsky A. , Demkov A. , Wang C. , Nguyen B.-Y. 
Published: April 2011

ABSTRACTAmorphous pure and Y-doped ZrO2 and HfO2 were prepared by precipitation with ammonia or hydrazine. Amorphous zirconium and hafnium silicates with SiO2 content from 10 to 90 mol % were prepared by sol-gel. Crystallization was studied by differential scanning calorimetry (DSC) at 20 °C/min and crystallite size after crystallization was determined from XRD data. ZrO2 crystallized into the tetragonal phase with ΔH -21 ±2 kJ/mol and HfO2 into the monoclinic phase with ΔH -31 ±2 kJ/mol. Doping with 20 at.% Y decreased crystallite size after crystallization. Crystallization temperatures for pure and Y-doped ZrO2 samples were in the range 420–440 °C. Crystallization temperatures for pure and Y-doped HfO2 samples varied from 470 to 570°C and correlate with surface area. Crystallization onset temperature in silicates increased with silica content from about 650 to 950 °C for ZrO2·SiO2 and from 740 to 1030 °C for HfO2·SiO2. Tetragonal zirconia and hafnia were the only crystalline phases formed below 1100 °C in all zirconium silicates and in hafnium silicates with more than 10 mol% SiO2. Crystallite size after crystallization decreased with increase in silica content. In hafnium silicate, a decrease in HfO2 crystallite size from 5 to 2.5 ±1 nm corresponds to a crystallization enthalpy change from -22 to -15 ±2 kJ/mol. The tetragonal HfO2/amorphous SiO2 interface energy can be calculated from calorimetric data as ∼0.25 J/m2. The critical particle size for the tetragonal to monoclinic transformation of HfO2 in HfO2-SiO2 system is about 6 nm. We predict that tetragonal HfO2 will be stabilized in films thinner than 2 nm.
Atomic Layer Deposition of High-k Gate Dielectrics Using MO Precursor and Cyclic Plasma Exposure
Authors: Endo Kazuhiko , Tatsumi Toru 
Published: April 2011

ABSTRACTWe have successfully achieved an ALD like deposition of ZrO2 or HfO2 by using a MO precursor. The MO precursor used in this study was zirconium tetra-tert-butoxide (ZTB) Zr(t-OC(CH3)3)4 and hafnium tetra-tert-butoxide (HTB) Hf(t-OC(CH3)3)4. Because MO precursors are very sensitive to H2O, we used oxygen plasma as an oxidizer instead of H2O in order to reduce background H2O pressure and suppress the background reaction. As a result, we successfully achieved an ALD-like deposition proved by a self-limiting adsorption of MO precursor. The carbon content in the films was suppressed due to highly reactive oxygen plasma. The leakage current of the film with plasma oxidation is much lower than that of film with H2O oxidation. Thus, MO-ALD using a plasma oxidation is a promising candidate for the high-k gate deposition process.
Measuring The Work Functions Of PVD TaN, TaSiN And TiSiN Films With A Schottky Diode CV Technique For Metal Gate CMOS Applications
Authors: Pan James , Woo Christy , Ngo Minh-Van , Tracy Bryan , Adem Ercan , Robie Stephen , Xiang Qi , Lin Ming-Ren 
Published: April 2011

ABSTRACTThe metal gate process becomes a promising candidate for sub-65nm CMOS, due to the elimination of polysilicon depletion effects, and the possibility of adjusting the CMOS threshold voltage without more threshold implants. Our goal is to process mteal films with tunable work functions, in order to meet the demand of sub-65nm metal gate CMOS.PVD TaN films are deposited with various processing conditions. Auger analysis shows that by changing the nitrogen flow rate and the plasma power, the nitrogen content in the TaN films can be adjusted. In order to accurately determine the work function of these TaN materials, we have developed a Schottky Diode CV technique (or Metal-Silicon CV, or MS-CV). This approach not only improves the accuracy of the metal work function measurement, compared with the traditional MOS-CV technique (which is affected by the thickness and quality of the oxide), but also simplifies the fabrication.With the MS-CV's, we have successfully measured the work functions of Ni and Co, and compared the data with published references. The work function of PVD TaN actually decreases with higher nitrogen content, according to the Auger data and the MS-CV measurement, ranging from 3.42 – 4.20 Volts. The MS-CV technique is shown to be independent to the size of the capacitors, and is little affected by the measurement frequency. By changing the frequency from 100KHz to 1MHz, the error in the work function is less than 50mV.
Trap Spectroscopy in Si3N4 Ultrathin Films Using Exoelectron Emission Method
Authors: Naich M. , Rosenman G. , Molotskii M. , Roizin Ya. 
Published: April 2011

ABSTRACTWe developed an original thermally stimulated exoelectron emission spectroscopy method (TSEE) of measurements of the activation energy Φ of electron (hole) traps in ultrathin Si3N4 films. The temperature spectra of TSEE of 50A silicon nitride films demonstrate several peaks: three low temperature peaks (T1 =373K, T2=423K, T3=498K) and a high temperature maximum at T4 ∼750K. The obtained values of the energy activation are Φ1=0.82 eV, Φ2=0.93 eV, Φ3=1.09 eV, and Φ4=1.73 eV. TSEE results are shown to be consistent with Φ estimates obtained from microFLASH® two bit per cell memory transistor measurements. Electrons stored at traps with Φ4=1.73 eV explain excellent microFlash retention properties. We believe that deep traps in Silicon Nitride are Hydrogen containing centers, while Hydrogen hopping is the route cause of observed material degradation in course of TSEE measurements.
Ultrathin Zirconium Dioxide Chemically Deposited at a Low Thermal Budget
Authors: Harasek Stefan , Wanzenboeck Heinz D. , Langfischer Helmut , Bertagnolli Emmerich 
Published: April 2011

ABSTRACTWe report on metal-organic chemical vapor deposition (MOCVD) of ultrathin zirconium dioxide on (100) silicon. Special emphasis is put on the evolution of surface topography and the impact of processing parameters on the chemical composition of the films. Electrical characterization by means of MOS structures has been performed to assess the interface quality and the dielectric properties of the layers. Interface trap density is observed to be around 5.1011 cm-2.eV-1 at midgap for (100)-oriented substrates. Leakage currents in the ultrathin regime are significantly reduced compared to equivalent SiO2-layers. Trap density and leakage current are strongly sensitive to annealing in different atmospheres. However, electrical characteristics are shown to be positively affected rather by annealing in slightly reducing than in oxidizing atmospheres. All temperatures throughout the gate insulator formation process do not need to exceed 650°C, and thus allow to keep the thermal budget low.
Oxygen vacancy defects in tantalum pentoxide: a density functional study
Authors: Ramprasad R. , Sadd Michael , Roberts Doug , Remmel Tom , Raymond Mark , Luckowski Eric , Kalpat Sriram , Barron Carole , Miller Mel 
Published: April 2011

ABSTRACTFirst principles total energy calculations were performed in order to characterize O vacancy defects in Ta2O5. A simplified version of the crystalline orthorhombic phase of Ta2O5 was used in this study. Results indicate that O vacancies in Ta2O5 can be broadly classified based on their location in the lattice. One type of vacancies (occupying the “in-plane” sites) displays deep or mid gap occupied states, and shallow unoccupied states, while a second type (occupying “cap” sites) results in shallow occupied states. For a wide range of local Fermi level or chemical potential, the neutral and +2 charged states of the in-plane type vacancy and the +2 charge state of the cap type vacancy are found to be most stable. Migration energies of the two types of vacancies in the neutral and +2 charge states are markedly different, with the “cap” type of vacancies displaying very high barriers to migration (∼ 5 eV) compared to the “in-plane” type (∼ 0.5–1.0 eV).