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GaN Electronics For High Power, High Temperature Applications

Description: A brief review is given of recent progress in fabrication of high voltage GaN and AlGaN rectifiers. GaN/AlGaN heterojunction bipolar transistors and GaN metal-oxide semiconductor field effect transistors. Improvements in epitaxial layer quality and in fabrication techniques have led to significant advances in device performance.
Date: June 12, 2000
Creator: PEARTON,S.J.; REN,F.; ZHANG,A.P.; DANG,G.; CAO,X.A.; LEE,K.P. et al.
Partner: UNT Libraries Government Documents Department

Structural TEM study of nonpolar a-plane gallium nitride grown on(112_0) 4H-SiC by organometallic vapor phase epitaxy

Description: Conventional and high resolution electron microscopy havebeen applied for studying lattice defects in nonpolar a-plane GaN grownon a 4H-SiC substrate with an AlN buffer layer. Samples in plan-view andcross-section configurations have been investigated. Basal and prismaticstacking faults together with Frank and Shockley partial dislocationswere found to be the main defects in the GaN layers. High resolutionelectron microscopy in combination with image simulation supported Drum smodel for the prismatic stacking faults. The density of basal stackingfaults was measured to be ~;1.6_106cm-1. The densities of partialdislocations terminating I1 and I2 types of intrinsic basal stackingfaults were ~;4.0_1010cm-2 and ~;0.4_1010cm-2, respectively. The energyof the I2 stacking fault in GaN was estimated to be (40+-4) erg/cm2 basedon the separation of Shockley partial dislocations. To the best of ourknowledge, the theoretically predicted I3 basal stacking fault in GaN wasobserved experimentally for the first time.
Date: April 5, 2005
Creator: Zakharov, Dmitri N.; Liliental-Weber, Zuzanna; Wagner, Brian; Reitmeier,Zachary J.; Preble, Edward A. & Davis, Robert F.
Partner: UNT Libraries Government Documents Department

Pyramidal Defects in GaN:Mg Grown with Ga Polarity

Description: Transmission electron microscopy (TEM) studies show formation of different types of Mg-rich defects in GaN. Types of defects strongly depend on crystal growth polarity. For bulk crystals grown with N-polarity, the planar defects are distributed at equal distances (20 unit cells of GaN). For growth with Ga-polarity (for both bulk and MOCVD grown crystals) a different type of defects have been found. These defects are three-dimensional Mg-rich hexagonal pyramids (or trapezoids) with their base on the (0001) plane and six walls formed on 1123 planes. The defects appear in [1120] and [1100] cross-section TEM micrographs as triangular and trapezoidal with sides inclined at 43 and 47 degrees to the base depending on the above observation directions, respectively. The dimension of these pyramids varies depending on growth method (50-1000 Angstrom), but the angle between the base and their sides remain the same. The direction from the tip of the pyramid to its base (and from the shorter to the longer base for trapezoidal defects) is along the Ga to N matrix bond direction. Analysis of the reconstructed exit wave phase image from the pyramid side indicates a shift of Ga atomic column positions from the matrix to the N position within the pyramid. In this way a 0.6{+-}0.2 Angstrom displacement can be measured on the pyramid side between Ga positions in the matrix and within the pyramid.
Date: February 15, 2005
Creator: Liliental-Weber, Zuzanna; Tomaszewicz, Tomasz; Zakharov, Dmitri & O'Keefe, Michael A.
Partner: UNT Libraries Government Documents Department

Remote operations in a global accelerator network

Description: The INTRODUCTION to this paper summarizes the history of the Global Accelerator Network (GAN) concept and the recent workshops that discussed the relationship between GAN and Remote Operations. The REMOTE OPERATIONS SCENARIOS section brings out the organizational philosophy embodied in GAN-like and to non-GAN-like scenarios. The set of major TOPICS RAISED AT THE WORKSHOPS are only partially resolved. COLLABORATION TOOLS are described and discussed, followed by examples of REMOTE ACCELERATOR CONTROL PROJECTS around the world.
Date: May 8, 2003
Creator: Peggs, Steve; Satogata, Todd; Agarwal, Deborah & Rice, David
Partner: UNT Libraries Government Documents Department

Electrical and optical properties of carbon-doped GaN grown by MBE on MOCVD GaN templates using a CCl4 dopant source

Description: Carbon-doped GaN was grown by plasma-assisted molecular-beam epitaxy using carbon tetrachloride vapor as the dopant source. For moderate doping mainly acceptors were formed, yielding semi-insulating GaN. However at higher concentrations p-type conductivity was not observed, and heavily doped films (>5 x 10{sup 20} cm{sup -3}) were actually n-type rather than semi-insulating. Photoluminescence measurements showed two broad luminescence bands centered at 2.2 and 2.9 eV. The intensity of both bands increased with carbon content, but the 2.2 eV band dominated in n-type samples. Intense, narrow ({approx}6 meV) donor-bound exciton peaks were observed in the semi-insulating samples.
Date: April 15, 2002
Creator: Armitage, Rob; Yang, Qing; Feick, Henning; Park, Yeonjoon & Weber, Eicke R.
Partner: UNT Libraries Government Documents Department

AlGaN Materials Engineering for Integrated Multi-Function Systems

Description: This LDRD is aimed to place Sandia at the forefront of GaN-based technologies. Two important themes of this LDRD are: (1) The demonstration of novel GaN-based devices which have not yet been much explored and yet are coherent with Sandia's and DOE's mission objectives. UV optoelectronic and piezoelectric devices are just two examples. (2) To demonstrate front-end monolithic integration of GaN with Si-based microelectronics. Key issues pertinent to the successful completion of this LDRD have been identified to be (1) The growth and defect control of AlGaN and GaN, and (2) strain relief during/after the heteroepitaxy of GaN on Si and the separation/transfer of GaN layers to different wafer templates.
Date: January 1, 2001
Partner: UNT Libraries Government Documents Department

Synthesis of rutherfordium isotopes in the 238U(26Mg, xn)264-xRf reaction and study of their decay properties

Description: Isotopes of rutherfordium (258-261Rf) were produced in irradiations of 238U targets with 26Mg beams. Excitation functions were measured for the 4n, 5n and 6n exit channels. Production of 261Rf in the 3n exit channel with a cross section of 28+92-26 pb was observed. Alpha decay of 258Rf was observed for the first time with an alpha-particle energy of 9.05+-0.03 MeV and an alpha/total decay branching ratio of 0.31+-0.11. In 259Rf, the electron capture/total decay branching ratio was measured to be 0.15+-0.04. The measured half-lives for 258Rf, 259Rf and 260Rf were 14.7+1.2-1.0 ms, 2.5+0.4-0.3 s and 22.2+3.0-2.4 ms, respectively, in agreement with literature data. The systematics of the alpha decay Q values and of the partial spontaneous fission half-lives were evaluated for even-even nuclides in the region of the N = 152, Z = 100 deformed shell. The influence of the N = 152 shell on the alpha decay Q values for rutherfordium was observed to be similar to that of the lighter elements (96<_ Z<_ 102). However, the N = 152 shell does not stabilize the rutherfordium isotopes against spontaneous fission, as it does in the lighter elements (96<_ Z<_102).
Date: January 15, 2008
Creator: Gates, Jacklyn M; Gates, J.M.; Garcia, M.A.; Gregorich, K.E.; Dullmann, Ch.E.; Dragojevic, I. et al.
Partner: UNT Libraries Government Documents Department

Intermixing and chemical structure at the interface between n-GaN and V-based contacts

Description: The interface between n-type GaN and V-based contacts was characterized by soft x-ray spectroscopy. We have investigated the chemical interface structure before and after a rapid thermal annealing (RTA) step, which is crucial for the formation of an Ohmic contact. X-ray photoelectron and x-ray excited Auger electron spectra suggestthat RTA induces an accumulation of metallic Ga at the surface. Using x-ray emission spectroscopy, we find that the probed nitrogen atoms are in a VN-like environment, indicating that vanadium interacts with nitrogen atoms from the GaN to form VN.
Date: June 30, 2008
Creator: Pookpanratana, S.; France, R.; Bar, M.; Weinhardt, L.; Fuchs, O.; Blum, M. et al.
Partner: UNT Libraries Government Documents Department

On the feasibility to investigate point defects by advanced electron microscopy

Description: Transmission Electron Microscopy evolves rapidly as a primary tool to investigate nano structures on a truly atomic level. Its resolution reaches into the sub Angstrom region by now. Together with a better correction of lens aberrations, sensitivities are drastically enhanced. Utilizing advanced electron microscopes, it is feasible to promote experiments that aim to detect single atoms. This enables local investigations of non-stoichiometry. This paper reviews the current state-of-the-art.
Date: October 2, 2002
Creator: Kisielowski, C. & Jinschek, J.R.
Partner: UNT Libraries Government Documents Department

Collaboration tools for the global accelerator network: Workshop Report

Description: The concept of a ''Global Accelerator Network'' (GAN) has been put forward as a means for inter-regional collaboration in the operation of internationally constructed and operated frontier accelerator facilities. A workshop was held to allow representatives of the accelerator community and of the collaboratory development community to meet and discuss collaboration tools for the GAN environment. This workshop, called the Collaboration Tools for the Global Accelerator Network (GAN) Workshop, was held on August 26, 2002 at Lawrence Berkeley National Laboratory. The goal was to provide input about collaboration tools in general and to provide a strawman for the GAN collaborative tools environment. The participants at the workshop represented accelerator physicists, high-energy physicists, operations, technology tool developers, and social scientists that study scientific collaboration.
Date: September 15, 2002
Creator: Agarwal, Deborah; Olson, Gary & Olson, Judy
Partner: UNT Libraries Government Documents Department

Microstructure and thermal stability of transition metal nitrides and borides on GaN

Description: Microstructure and thermal stability of ZrN/ZrB2 bilayer deposited on GaN have been studied using transmission electron microscopy methods (TEM) and secondary ion mass spectrometry (SIMS). It has been demonstrated that annealing of the contact structure at 1100 C in N2 atmosphere does not lead to any observable metal/ semiconductor interaction. In contrast, a failure of the integrity of ZrN/ZrB2 metallization at 800 C, when the heat treatment is performed in O2 ambient has been observed.
Date: June 28, 2000
Creator: Jasinski, J.; Kaminska, E.; Piotrowska, A.; Barcz, A. & Zielinski, M.
Partner: UNT Libraries Government Documents Department

Formation of ohmic contacts to MOCVD grown p-GaN by controlled activation of Mg

Description: We report on the formation of low resistivity ohmic contacts to p-GaN, r{sub c} &lt; 10{sup {minus}4}{Omega}cm{sup 2}, by increasing the concentration of the active Mg in the subcontact zone, via Zr-mediated release of hydrogen. We have investigated the process of evolution of hydrogen from MOCVD grown p-GaN via Zr-based metallization, and determined the optimum processing conditions (temperature and gas ambient) for fabrication of low resistance ohmic contacts. When the process is conducted in N{sub 2} flow, the metallization remains stable at temperatures required to achieve the ohmic behavior, and the morphology of the metal/semiconductor interface is unaltered by such a heat treatment. The processing in O{sub 2}, on the contrary, causes the interdiffusion of metallization constituents and the incorporation of oxygen into the semiconductor subcontact region, which could be responsible for increased resistivity of these contacts.
Date: November 27, 2000
Creator: Kaminska, E.; Piotrowska, A.; Barcz, A.; Bour, D.; Zielinski, M. & Jasinski, J.
Partner: UNT Libraries Government Documents Department

Selective excitation of the yellow luminescence of GaN

Description: The yellow luminescence of n-type GaN has been studied with selective excitation using a combination of Ar ion and dye lasers. Narrower structures whose peak energies follow the excitation photon energy over the width of the yellow luminescence have been observed. Unlike the yellow luminescence excited by above band gap excitations, these fine structures exhibits thermal activated quenching behavior. We propose that these fine structures are due to emission occurring at complexes of shallow donors and deep acceptors which can be resonantly excited by photons with energies below the band gap. The activation energy deduced from their intensity is that for delocalization of electrons out of the complexes. Our results therefore suggest that there is more than one recombination channel (usually assumed to be due to distant donor-acceptor pairs) to the yellow luminescence in GaN.
Date: July 1, 1999
Creator: Colton, J. S.; Yu, P. Y.; Teo, K. L.; Weber, E. R.; Grzegory, I. & Uchida, K.
Partner: UNT Libraries Government Documents Department

Improved heteroepitaxial MBE GaN growth with a Ga metal buffer layer

Description: We demonstrate that the use of pure gallium (Ga) as a buffer layer results in improved crystal quality of GaN epilayers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire. The resulting epilayers show electron Hall mobilities as high as 400 cm 2 /Vs at a background carrier concentration of 4 x 10 17 cm -3 , an outstanding value for an MBE-grown GaN layer on sapphire. Structural properties are also improved; the asymmetric (101) X-ray rocking curve width is drastically reduced with respect to that of the reference GaN epilayer grown on a low-temperature GaN buffer layer. Nitrided Ga metal layers were investigated for different Ga deposition time. These layers can be regarded as templates for the subsequent Ga main layer growth. It was found that there is an optimum Ga metal layer deposition time for improving the electron mobility in the epilayer. Heating of the Ga metal layer to the epilayer growth temperature under nitrogen plasma is found to be sufficient to produce highly oriented GaN crystals. However, nonuniform surface morphology and incomplete surface coverage were observed after nitridation of comparatively thick Ga metal layers. This is shown to be the reason for the decreasing electron mobility of the epilayers as the Ga metal layer thickness exceeds the optimum value.
Date: May 15, 2000
Creator: Kim, Yihwan; Subramanya, Sudhir G.; Krueger, Joachim; Siegle, Henrik; Shapiro, Noad; Armitage, Robert et al.
Partner: UNT Libraries Government Documents Department

Lattice-matched HfN buffer layers for epitaxy of GaN on Si

Description: Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 (mu)m. Initial results for GaN grown on the (111) surface show a photoluminescence peak width of 17 meV at 11 K, and an asymmetric x-ray rocking curve width of 20 arcmin. Wurtzite GaN on HfN/Si(001) shows reduced structural quality and peculiar low-temperature luminescence features. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.
Date: May 8, 2002
Creator: Armitage, Robert; Yang, Qing; Feick, Henning; Gebauer, Joerg; Weber, Eicke R.; Shinkai, Satoko et al.
Partner: UNT Libraries Government Documents Department

Screw dislocations in GaN

Description: GaN has received much attention over the past few years because of several new applications, including light emitting diodes, blue laser diodes and high-power microwave transistors. One of the biggest problems is a high density of structural defects, mostly dislocations, due to a lack of a suitable lattice-matched substrate since bulk GaN is difficult to grow in large sizes. Transmission Electron Microscopy (TEM) has been applied to study defects in plan-view and cross-sections on samples prepared by conventional techniques such as mechanical thinning and precision ion milling. The density of dislocations close to the sample surface of a 1 mm-thick HVPE sample was in the range of 3x109 cm-2. All three types of dislocations were present in these samples, and almost 50 percent were screw dislocations. Our studies suggest that the core structure of screw dislocations in the same material might differ when the material is grown by different methods.
Date: February 15, 2002
Creator: Liliental-Weber, Zuzanna; Jasinski, Jacek B.; Washburn, Jack & O'Keefe, Michael A.
Partner: UNT Libraries Government Documents Department

Benefits of microscopy with super resolution

Description: Transmission Electron Microscopy developed from an imagingtool into a quantitative electron beam characterization tool that locallyaccesses structure, chemistry, and bonding in materials with sub Angstromresolution. Experiments utilize coherently and incoherently scatteredelectrons. In this contribution, the interface between gallium nitrideand sapphire as well as thin silicon gate oxides are studied tounderstand underlying physical processes and the strength of thedifferent microscopy techniques. An investigation of the GaN/sapphireinterface benefits largely from the application of phase contrastmicroscopy that makes it possible to visualize dislocation corestructures and single columns of oxygen and nitrogen at a closest spacingof 85 pm. In contrast, it is adequate to investigate Si/SiOxNy/poly-Siinterfaces with incoherently scattered electrons and electronspectroscopy because amorphous and poly crystalline materials areinvolved. Here, it is demonstrated that the SiOxNy/poly-Si interface isrougher than the Si/SiOx interface, that desirable nitrogen diffusiongradients can be introduced into the gate oxide, and that a nitridationcoupled with annealing increases its physical width while reducing theequivalent electrical oxide thickness to values approaching 1.2 nm.Therefore, an amorphous SiNxOy gate dielectric seems to be a suitablesubstitute for traditional gate oxides to further increase device speedby reducing dimensions in Si technology.
Date: July 9, 2001
Creator: Kisielowski, C.; Principe, E.; Freitag, B. & Hubert, D.
Partner: UNT Libraries Government Documents Department

Low Cost Production of InGaN for Next-Generation Photovoltaic Devices

Description: The goal of this project is to develop a low-cost and low-energy technology for production of photovoltaic devices based on InGaN materials. This project builds on the ongoing development by Structured Materials Industries (SMI), of novel thin film deposition technology for Group III-Nitride materials, which is capable of depositing Group-III nitride materials at significantly lower costs and significantly lower energy usage compared to conventional deposition techniques. During this project, SMI demonstrated deposition of GaN and InGaN films using metalorganic sources, and demonstrated compatibility of the process with standard substrate materials and hardware components.
Date: July 9, 2012
Creator: Nick M. Sbrockey, Shangzhu Sun, Gary S. Tompa,
Partner: UNT Libraries Government Documents Department

Imaging columns of the light elements carbon, nitrogen and oxygen with sub angstrom resolution

Description: It is reported that lattice imaging with a 300 kV field emission microscope in combination with numerical reconstruction procedures can be used to reach an interpretable resolution of about 80 pm for the first time. A retrieval of the electron exit wave from focal series allows for the resolution of single atomic columns of the light elements carbon, nitrogen, and oxygen at a projected nearest neighbor spacing down to 85 pm. Lens aberrations are corrected on-line during the experiment and by hardware such that resulting image distortions are below 80 pm. Consequently, the imaging can be aberration-free to this extent. The resolution enhancement results from increased electrical and mechanical stability's of the instrument coupled with a low spherical aberration coefficient of 0.595 + 0.005 mm.
Date: January 2, 2000
Creator: Kisielowski, C.; Hetherington, C.J.D.; Wang, Y.C.; Kilaas, R.; O'Keefe, M.A. & Thust, A.
Partner: UNT Libraries Government Documents Department

Simulation of Npn and Pnp AlGaN/GaN heterojunction bipolar transistors performances: Limiting factors and optimum design

Description: The performance capabilities of Npn and Pnp AlGaN/GaN heterojunction bipolar transistors have been investigated by using a drift-diffusion transport model. Numerical results have been employed to study the effect of the p-type Mg doping and its incomplete ionization on device performance. The high base resistance induced by the deep acceptor level is found to be the cause of limited current gain values for Npn devices. Several computation approaches have been considered to improve their performance. Reasonable improvement of the DC current gain {beta} is observed by realistically reducing the base thickness in accordance with processing limitations. Base transport enhancement is also predicted by the introduction of a quasi-electric field in the base. The impact of the base resistivity on high-frequency characteristics is investigated for Npn AlGaN/GaN devices. Optimized predictions with maximum oscillation frequency value as high as f{sub MAX} = 20 GHz and a unilateral power gain--U = 25 dB make this bipolar GaN-based technology compatible with communication applications. Simulation results reveal that the restricted amount of free carriers from the p-doped emitter limits Pnp's DC performances operating in common emitter configuration. A preliminary analysis of r.f. characteristics for the Pnp counterpart indicates limited performance mainly caused by the degraded hole mobility.
Date: April 25, 2000
Partner: UNT Libraries Government Documents Department

The Effects of Residual Gases on the Field Emission Properties of ZnO, GaN, ZnS Nanostructures, and the Effects of Light on the Resistivity of Graphene

Description: In this dissertation, I present that at a vacuum of 3×10-7 Torr, residual O2, CO2, H2 and Ar exposure do not significantly degrade the field emission (FE) properties of ZnO nanorods, but N2 exposure significantly does. I propose that this could be due to the dissociation of N2 into atomic nitrogen species and the reaction of such species with ZnO. I also present the effects of O2, CO2, H2O, N2, H2, and Ar residual gas exposure on the FE properties of GaN and ZnS nanostructure. A brief review of growth of ZnO, GaN and ZnS is provided. In addition, Cs deposition on GaN nanostructures at ultra-high vacuum results in 30% decrease in turn-on voltage and 60% in work function. The improvement in FE properties could be due to a Cs-induced space-charge layer at the surface that reduces the barrier for FE and lowers the work function. I describe a new phenomenon, in which the resistivity of CVD-grown graphene increases to a higher saturated value under light exposure, and depends on the wavelength of the light—the shorter the wavelength, the higher the resistivity. First-principle calculations and theoretical analysis based on density functional theory show that (1) a water molecule close to a graphene defect is easier to be split than that of the case of no defect existing and (2) there are a series of meta-stable partially disassociated states for an interfacial water molecule. Calculated disassociation energies are from 2.5 eV to 4.6 eV, that match the experimental observation range of light wavelength from visible to 254 nm UV light under which the resistivity of CVD-grown graphene is increased.
Date: May 2014
Creator: Mo, Yudong
Partner: UNT Libraries

Role of defects in III-nitride based electronics

Description: The LDRD entitled ``Role of Defects in III-Nitride Based Devices'' is aimed to place Sandia National Laboratory at the forefront of the field of GaN materials and devices by establishing a scientific foundation in areas such as material growth, defect characterization/modeling, and processing (metalization and etching) chemistry. In this SAND report the authors summarize their studies such as (1) the MOCVD growth and doping of GaN and AlGaN, (2) the characterization and modeling of hydrogen in GaN, including its bonding, diffusion, and activation behaviors, (3) the calculation of energetic of various defects including planar stacking faults, threading dislocations, and point defects in GaN, and (4) dry etching (plasma etching) of GaN (n- and p-types) and AlGaN. The result of the first AlGaN/GaN heterojunction bipolar transistor is also presented.
Date: January 1, 2000
Partner: UNT Libraries Government Documents Department

Measurement of the indium segregation in InGaN based LEDs with single atom sensitivity

Description: In light emitting diodes (LED) consisting of GaN/InGaN/GaN quantum wells (QWs), the exact indium distribution inside the wells of the active region affects the performance of devices. Indium segregation can take place forming small InGaN clusters of locally varying composition. In the past, we used a local strain analysis from single HRTEM lattice images to determine the In composition inside the InGaN QWs with a resolution of 0.5 nm x 0.3 nm. Truly atomic resolution can be pursued by exploitation of intensity dependencies on the atomic number (Z) of the electron exit-wave (EW). In microscopes with sufficient sensitivity, local variations of amplitude and phase are found to be discrete with sample thickness, which allows for counting the number of atoms in each individual column of {approx}0.08 nm diameter. In QW s of {approx}17 percent of average indium concentration it is possible to discriminate between pure Ga columns and columns containing 1, 2, 3, or more In atoms because phase changes are discrete and element specific. The preparation of samples with atomically flat surfaces is a limiting factor for the application of the procedure.
Date: July 30, 2003
Creator: Jinschek, Joerg; Kisielowski, Christian; Van Dyck, Dirk & Geuens, Philippe
Partner: UNT Libraries Government Documents Department