bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low-Electron-Energy Cathodoluminescence Study Of Polishing And Etching Effects On The Optical Properties Of Bulk Single-Crystal Gallium Nitride
Authors: Robins Lawrence H. , Steiner Bruce , Sanford Norman A. , Menoni Carmen 
Published: April 2011

ABSTRACTLow electron energy cathodoluminescence (LEECL) was used to examine polishing-induced damage in a bulk high-pressure grown GaN single-crystal platelet. The Ga-polarity face of the platelet was mechanically polished; chemically-assisted ion-beam etching (CAIBE) to a depth of 200 nm was performed on a portion of this face. Low-temperature (15 K) CL spectra of the polished-only and polished+CAIBE regions of the Ga-face were taken at 2.8 kV, 5.4 kV, and 10.6 kV (corresponding to average electron penetration depths of 19 nm, 56 nm, and 170 nm). The low-temperature CL spectrum of the unpolished, N-polarity face was taken at 10.6 kV. In the near-band-edge region, all the CL spectra from the Ga-polarity face show a narrow peak near 3.47 eV, ascribed to donor-bound exciton recombination, and several overlapping peaks at lower energy (3.1 eV to 3.4 eV), ascribed to defect-related levels or to donor-acceptor pair recombination. Functional curve-fitting analysis enabled deconvolution of the spectra into the sum of an asymmetric peak (the donor-bound exciton) and several symmetric Gaussian peaks (the lower energy, defect-related or donor-acceptor peaks). The linewidth of the donor-bound exciton peak decreased with increasing penetration depth, and also decreased on going from the polished-only to the polished+CAIBE region. The relative intensity of a defect-related peak at ≈3.325 eV showed a similar decreasing trend with increasing penetration depth or with CAIBE treatment. The LEECL results suggest that the thickness of the polishing damage layer is approximately 400 nm; the 200 nm CAIBE step is thus insufficient to completely remove the damage.
Photoreflectance Probing of Below Gap States in Gan/Algan High Electron Mobility Transitor Structures
Authors: Gaskill D. K. , Glembocki O. J. , Peres B. , Henry R. , Koleske D. , Wickenden A. 
Published: April 2011

ABSTRACTOptical Impedence Spectroscopy of GaN/AlGaN high electron mobility transistor structures (HEMTs) using photoreflectance exhibit a photoreflectance lags – the component of the modulated reflectance out of phase with the chopper – ranging from 0.1 to 0.5. Photoreflectance was performed using below gap pumping on various samples. Samples that do exhibit appreciable photoreflectance lag for above gap pumping show significantly enhanced photoreflectance signals for below gap pumping. Yet, samples that do not exhibit appreciable photoreflectance lag for above gap pumping do not exhibit a signal for below gap pumping. This implies that the photoreflectance phase lag is due to mid-gap trap states. At least 2 types of traps are found, above and below about 2.5 eV. This result means that that photoreflectance can be used as a probe of HEMT device quality.
Compositional Fluctuations in AlxGa1-xN Layers grown on 6H-SiC (0001) by Metal Organic Vapor Phase Epitaxy
Authors: Kröger R. , Einfeldt S. , Reitmeier Z. J. , Chierchia R. , Ryder P. , Hommel D. , Davis R. F. 
Published: April 2011

ABSTRACTThe microstructural evolution of AlxGa1-xN films grown by metalorganic vapor phase epitaxy on 6H-SiC (0001) was studied by means of X-ray diffraction, atomic force microscopy and transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy. A significant spatial variation of composition was found in 100 nm thick layers the nature of which could be traced back to the initial stage of film formation. Upon nucleation two phases are formed: a wetting layer and isolated islands of high and low aluminum content, respectively. The observed results are discussed in terms of strain and growth rates.
Photoreflectance Characterization and Control of Defects in Gan by Etching with an Inductively Coupled Plasma
Authors: Glembocki O. J. , Gaskill D. K. , Prokes S. M. , Pearton S. W. 
Published: April 2011

ABSTRACTPhotoreflectance (PR) is used to detect and characterize the electronic effects etch-induced defects in GaN that is exposed to an Ar or Ar/Cl inductively coupled plasma (ICP). Because of the sensitivity of PR we can follow the formation of etch-induced defects as a function of ion energies and densities. We show that at low RF powers, below 100W, the surface improves in electronic quality, but as the power is increased beyond 200W, etch-induced defects, are formed. The use of an Ar/Cl mixture plays a critical role in control of etch-induced defects.
Optical Characterization of High Quality GaN Produced by High Rate Magnetron Sputter Epitaxy
Authors: Park Minseo , Carlson E. , Chang Y. C , Muth J. F. , Bumgarner J. , Kolbas R. M. , Cuomo J. J. , Nemanich R. J. 
Published: April 2011

ABSTRACTThe thick films of GaN were investigated using X-ray diffraction, micro-Raman spectroscopy and photoluminescence spectroscopy. The thick films of GaN were prepared on (0001) sapphire using high rate magnetron sputter epitaxy with growth rates as high as 10–60 m/min. The width of the X-ray rocking curve ((0002) reflection) for the sample produced by this method is ∼300 arc-sec. Only the allowed modes were observed in the polarized Raman spectra. The background electron concentration is lower than 3×1016 cm−3, which was determined from the Raman spectra. The phonon lifetime determined from Raman E2(2) mode was 1.6 ps, which is comparable to that of bulk single crystal GaN grown by sublimation (1.4 ps). The full-width-at-half-maximum of the near band-edge photoluminescence peak obtained at 77K is ∼100 meV.
Subpicosecond Luminescence Studies of Carrier Dynamics in Nitride Semiconductors Grown Homoepitaxially By MBE On GaN Templates
Authors: Garrett G. A. , Sampath A. V. , Collins C. J. , Semendy F. , Aliberti K. , Shen H. , Wraback M. , Fedyunin Y. , Moustakas T. D. 
Published: April 2011

ABSTRACTA new technique is presented that employs luminescence downconversion using an ultrashort gating pulse to enable the characterization of UV light emission from III-nitride semiconductors with subpicosecond temporal resolution. This technique also allows one to measure PL rise times and fast components of multiple decays in the subsequent time evolution of the PL intensity. Comparison of luminescence emission intensity and lifetime in GaN and AlGaN with ∼0.1 Al content grown homoepitaxially on GaN templates with the same quantities measured in heteroepitaxial layers grown on sapphire indicate significant improvement in the homoepitaxial layers due to reduction in dislocation density. Fast (<15 ps) initial decays in the AlGaN are attributed to localization associated with alloy fluctuations and subsequent recombination through gap states.
Lattice Location and Cathodoluminescence Studies of Ytterbium/Thulium Implanted 2H-Aluminium Nitride
Authors: Vetter U. , Reid M. F. , Hofsäss H. , Ronning C. , Zenneck J. , Dietrich M. 
Published: April 2011

ABSTRACTLattice location studies of radioactive 169Yb ions, implanted at an energy of 60 keV into 2H-AlN at the on-line isotope separator ISOLDE at CERN, were performed using the emission channeling technique. The measurements, which yield a substitutional Al lattice site for the implanted ions, were recorded for annealing temperatures ranging from 293 K to 1273 K. After complete decay of 169Yb to 169Tm cathodoluminescence measurements were performed in the range 12 K – 300 K. The samples show a strong visible luminescence at 460 - 470 nm at room temperature, which is attributed to the 1D2−3F4 intra-4f electron transition of Tm3+. At 12 K the luminescence is dominated by transitions starting from the 1H6 multiplet. Time resolved as well as temperature dependent cathodoluminescence measurements are presented and discussed.The lattice location as well as the time resolved cathodoluminescence measurements suggest that there is only one pronounced site of the implanted ions in the AlN lattice and that this is the substitutional aluminium site.
Molecular Beam Epitaxial Growth of AlN/GaN Multiple Quantum Wells
Authors: Wu Hong , Schaff William J. , Koley Goutam , Furis Madalina , Cartwright A. N. , Mkhoyan Karen A. , Silcox John , Henderson Walter , Alan Doolittle W. , Osinsky A. V. 
Published: April 2011

ABSTRACTAlN/GaN multiple quantum wells (MQWs) were grown on sapphire substrates by plasmaassisted molecular beam epitaxy. Growth temperature, III/V ratio, growth rate, and other growth parameters were optimized for the buffer layer and the MQWs, separately. The growth of AlN buffer was kept as Al-rich as possible while the formation of Al droplets was avoided. A GaN buffer layer was also tried but proved to be inferior to AlN buffer probably due to its larger surface roughness, higher dislocation density, and larger lattice mismatch with the AlN barrier layers in the MQWs. Very flat surfaces with a RMS roughness of 0.7nm were observed by atomic force microscopy (AFM) on the samples with both AlN buffer layer and 20 MQWs deposited under the optimized growth conditions. Abrupt interfaces and excellent periodicities of the MQWs were confirmed by X-ray diffraction (XRD) and reflectivity measurements with MQWs' satellite peaks clearly visible up to the 10th order. Room-temperature intense ultraviolet (UV) photoluminescence (PL) emission with wavelength in the range of 320–350nm was also observed from the MQWs with well width ranging from 1.0 to 1.5nm. These MQW structures can potentially be used for UV light emitters and quantum cascade lasers.
Growth and Characterization of Deep UV Emitter Structures Grown on Single Crystal Bulk AlN Substrates
Authors: Hu X. , Gaska R. , Chen C. , Yang J. , Kuokstis E. , Khan A. , Tamulaitis G. , Yilmaz I. , Shur M. S. , Rojo J. C. , Schowalter L. J. 
Published: April 2011

ABSTRACTWe report on high Al-content AlGaN-based deep UV emitter structures grown over single crystal, slightly off c-axis (5.8 degrees) bulk AlN substrates. AlN/AlGaN multiple quantum well (MQW) structures with up to 50% of Al in the well material were grown by using low-pressure MOCVD and characterized by using X-ray, AFM, SEM and photoluminescence techniques. Two light sources, one at 213 nm wavelength for selective excitation of quantum well layers and another one at 193 nm to excite both wells and barriers, were exploited. A weak temperature dependence (from 8 K to 300 K) of the luminescence intensity and the absence of blue-shift of the luminescence peak with increasing excitation intensity pointed to a low density of localized states, in a good agreement with the X-ray data, which indicated very high quality of these MQW structures.The most striking result was observation of stimulated emission at wavelength as short as 258 nm in Al0.5Ga0.5N/AlN MQWs grown on bulk AlN single crystals.
Properties of Surface Acoustic Waves in AlN And GaN
Authors: Deng Jianyu , Ciplys Daumantas , Bu Gang , Shur Michael , Gaska Remis 
Published: April 2011

ABSTRACTThe surface acoustic wave velocities, electromechanical coupling coefficients, and the spatial distributions of both elastic displacement and electric potential have been calculated for various configurations of gallium nitride and aluminum nitride. The electromechanical coupling coefficient values of 0.13 % in GaN and 0.29 % in AlN have been predicted. The maximum electromechanical coupling coefficient values of 0.24 % at Euler angles (0, 54°, 90°) in GaN and 1.08 % at (0, 53°, 90°) in AlN have been found. For GaN layer-on- sapphire substrate structures, the SAW velocity and electromechanical coupling coefficient have been calculated as functions of layer thickness and acoustic wavelength. The experimentally measured values of the surface acoustic wave velocity and electromechanical coupling coefficient are in satisfactory agreement with the calculation results.
Indium distribution inside quantum wells: The effect of growth interruption in MBE
Authors: Sanchez A. M. , Ruterana P. , Kret S. , Dłużewski P. , Maciejewski G. , Grandjean N. , Damilano B. 
Published: April 2011

ABSTRACTQuantitative analysis of high resolution electron microscopy image has been carried out to measure the indium distribution inside InGaN/GaN quantum well. The analyzed samples were nominally grown with 15% indium composition by molecular beam epitaxy with interruptions during the InxGa1-xN layer growth. The strain distribution is not homogeneous inside the quantum wells, and indium rich clusters can be observed. Areas with almost no indium concentration were observed corresponding to the growth interruption. A comparison with samples grown by metalorganic chemical vapor deposition is attempted.
New UV Light Emitter Based on AlGaN Heterostructures with Graded Electron and Hole Injectors
Authors: Johnson M.A.L. , Long J.P. , Schetzina J. F. 
Published: April 2011

ABSTRACTNew ultraviolet (UV) light emitting device structures address the problems of small carrier concentrations and large band-offsets in wide bandgap Aluminum Gallium Nitride (AlGaN) heterostructures through the use of graded epilayers for electron and hole injection. For light emission at 280–290 nm, a multiple-quantum-well separate confinement heterostructure (MQWSCH) employs a graded AlGaN structure for the injection of majority carriers from the metal-semiconductor contact layers into the spacecharge region of the pn-junction with a higher bandgap energy. Sample LED mesa devices were fabricated and have shown light emission of 289 nm under a forward bias of 12V (20mA). These results provide a ‘proof-of-concept’ for this new graded device structure which can be employed for the development of both UV-LEDs and laser diodes.
High Performance HFET Devices on Sapphire and SiC: Passivation with AlN
Authors: Bardwell Jennifer A. , Liu Ying , Webb James B. , Tang Haipeng , Rolfe Stephen J. , Lapointe Jean 
Published: April 2011

ABSTRACTAlGaN/GaN two dimensional electron gas (2DEG) heterostructures were grown by ammonia-MBE on sapphire and SiC substrates. Devices fabricated from these optimized HFET layers, with optically defined gates showed excellent characteristics, e.g. a maximum drain current density of 1.3 A/mm, maximum transconductance of 220 mS/mm, fT of 15.6 GHz and fMAX of 58.1 GHz was measured for devices with 0.9 μm gate length and 40 μm gate width. Shorter gate length devices exhibited higher frequency responses: fT of 68 GHz and fMAX of 125 GHz for 0.25 μm gate length and fT of 103 GHz and fMAX of 170 GHz for 0.15 μm gate length. However, these devices showed “current collapse” when subjected to load pull measurements. Current collapse was also observed in sequentially repeated DC measurements in the dark, both on sapphire and SiC substrates, although the degree of collapse varied greatly from one wafer to another. One method of reducing the current collapse was to apply a thin (100 - 6000 Å) magnetron sputtered AlN passivation layer (over the gates) or a 500 Å layer under the gates so that MISFET devices were obtained. The electrical characteristics of the passivated and unpassivated devices are discussed.
Physcial characterization of ultrathin high k dielectrics
Authors: Vandervorst W. , Brijs B. , Bender H. , Conard O. T. , Petry J. , Richard O. , Van Elshocht S. , Delabie A. , Caymax M. , De Gendt S. 
Published: April 2011

ABSTRACTTargeting very thin equivalent oxides (<1 nm) requires the deposition of (very) thin dielectrica onto silicon surfaces with minimal interfacial oxide. Typically, high-k dielectric layers are deposited using ALD or MOCVD with, at present, a prime emphasis on Hf-based high-k dielectrics, either as pure HfO2, as silicate or mixed with Al2O3. In some cases nitrogen is added to improve the high-temperature stability. Depending on the deposition conditions ALD as well as MOCVD show serious deficiencies in terms of film closure and material density for ultra thin (<3 nm) films. Various surface preparation methods and deposition conditions are used to improve the film quality. Detailed studies on the film growth and its evolution requires the use of many analytical methods such as Rutherford Backscattering Spectrometry, Low Energy Ion Scattering, Time-of-flight SIMS, (spectroscopic) ellipsometry and X-ray photoelectron spectroscopy. When trying to correlate the results in terms of film thickness, apparent discrepancies can be observed which relate to non-homogeneous growth and reduced material density.
In Situ Spectroscopic Approach to Atomic Layer Deposition
Authors: Frank Martin M. , Chabal Yves J. , Wilk Glen D. 
Published: April 2011

ABSTRACTThere is great need for a mechanistic understanding of growth chemistry during atomic layer deposition (ALD) of films for electronic applications. Since commercial ALD reactors are presently not equipped for in situ spectroscopy, we have constructed a model reactor that enables single-pass transmission infrared spectroscopy to be performed in situ on a layer-by-layer basis. We demonstrate the viability of this approach for the study of aluminum oxide growth on silicon surfaces, motivated by alternative gate oxide applications. Thanks to submonolayer dielectric and adsorbate sensitivity, we can quantify oxide thicknesses and hydroxyl areal densities on thermal and chemical SiO2/Si(100) substrates. Methyl formation and hydroxyl consumption upon initial trimethylaluminum (TMA) reaction can also be followed. We verify that in situ grown Al2O3 films are compatible in structure to films grown in a commercial ALD reactor.
Characterization of Ruthenium and Ruthenium Oxide Thin Films deposited by Chemical Vapor Deposition for CMOS Gate Electrode Applications
Authors: Papadatos Filippos , Skordas Spyridon , Consiglio Steve , Kaloyeros Alain E. , Eisenbraun Eric 
Published: April 2011

ABSTRACTThis study describes work carried out to date involving evaluation of the chemical, structural, and electrical performance of ruthenium (Ru) and ruthenium oxide (RuO2) films grown on SiO2 substrates employing metal organic chemical vapor deposition (MOCVD). Diethyl ruthenocene and oxygen were employed as reactant gases for this work, which was carried out using a 200mm wafer cluster tool. The films were characterized using cross-sectional scanning electron microscopy (CS-SEM), four-point resistance probe, x-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), x-ray diffraction (XRD), and energy dispersive spectrometry (EDS). Capacitance-voltage (C-V) measurements were also carried out to assess the work function of the deposited films. It was determined that both Ru and RuO2 phases possess near-bulk resistivity and low contamination levels. Importantly, it was observed that the film stoichiometry could be modulated by controlled changes of the processing conditions, and that pure Ru and RuO2 films can be deposited in an oxygen ambient. In order to assess thermal stability, the films were subsequently annealed in forming gas and oxygen ambients, and it was found that the film stability is dependent upon both the deposited phase and the annealing ambient. Results of PMOS gate electrode performance testing of CVD Ru films, has been carried out, and the results are similar to those previously reported for ruthenium-based films.
The Effect of SiGe Barriers on the Thermal Stability of Highly B-Doped Si Surface Layers
Authors: Thompson Phillip E. , Bennett Joe , Crosby Robert , Twigg Mark E. 
Published: April 2011

ABSTRACTWe have investigated the use of low-temperature (320 °C) molecular-beam epitaxy (MBE) to form highly conductive, p+, ultra-shallow layers in Si. Although the as-grown B-doped Si is electrically active, in a practical application the doped layers may be exposed to high temperature during post-growth device processing. To minimize the B diffusion, we investigated the use of SiGe diffusion barrier layers. In this work we demonstrate there is less B redistribution with the SiGe diffusion barriers. The use of SiGe diffusion barriers may prove to be critical in the activation of B implants for the formation of ultra-shallow junctions.
Strained-Si-on-Insulator (SSOI) and SiGe-on-Insulator (SGOI): Fabrication Obstacles and Solutions
Authors: Taraschi Gianni , Pitera Arthur J. , McGill Lisa M. , Cheng Zhi-Yuan , Lee Minjoo L. , Langdo Thomas A. , Fitzgerald Eugene A. 
Published: April 2011

ABSTRACTAdvanced CMOS substrates composed of ultra-thin strained-Si and SiGe-on-insulator were fabricated, combining both the benefits of high-mobility strained-Si and SOI. Our pioneering method employed wafer bonding of SiGe virtual substrates (with strained-Si layers) to oxidized handle wafers. Layer transfer onto insulating handle wafers can be accomplished using grind-etchback or delamination via implantation. Both methods were found to produce a rough transferred layer, but polishing is unacceptable due to non-uniform material removal across the wafer and the lack of precise control over the final layer thickness. To solve these problems, a strained-Si stop layer was incorporated into the bonding structure. After layer transfer, excess SiGe was removed using a selective etch process, stopping on the strained-Si. Within the context of ultra-thin SSOI and SGOI fabrication, this paper describes recent improvements including metastable stop layers, low temperature wafer bonding, and improved selective SiGe removal.
Electrical and Structural Characterization of HfO2 MIM Capacitors
Authors: Yang Fan , Kotecki David E. 
Published: April 2011

ABSTRACTHafnium oxide is a promising dielectric for future microelectronic applications. HfO2 thin films (10–75nm) were deposited on Pt/SiO2/Si and quartz substrates by Pulsed DC magnetron reactive sputtering. Top electrodes of Pt were formed by e-beam evaporation through an aperture mask on the HfO2/Pt/SiO2/Si samples to create MIM capacitors. Various process conditions (Ar/O2 ratio, DC power, and deposition rate) and post-deposition annealing conditions (time and temperature) were investigated. The structure of the HfO2 films was characterized by X-ray diffraction (XRD) and the roughness was measured by a profilometer. The electrical properties were characterized in terms of their relative permittivity (εr(T) and εr(f)), and leakage behavior (I-V and I-t). The electrical measurements were performed over a temperature range from –5 to 200°C. For the best samples, the relative permittivity of HfO2 was found to be ∼27 after anneal and increased by 0.027%/°C with increasing temperature over the measured temperature range. At 25°C, leakage current density was below 10-8 A/cm2 at 1 volt. The optical bandgap was measured to be 5.4eV after anneal.
Oriented Growth of Thin Films of Samarium Oxide by MOCVD
Authors: Shalini K. , Shivashankar S. A. 
Published: April 2011

ABSTRACTThin films of samarium oxide, Sm2O3, have been grown on Si(100) and fused quartz by low-pressure MOCVD using an adducted β-diketonate precursor developed in house. It is found that the nature of the film grown is strongly dependent on substrate temperature. As examined by X-ray diffraction, the films of Sm2O3 grown at lower temperatures (∼550°C) on fused quartz are cubic and display a random grain orientation, while they become highly oriented in the (111) direction as the growth temperature is increased (to 625°C). On Si(100), highly oriented films of cubic Sm2O3 are obtained at a substrate temperature of 625°C. When the growth temperature is raised, the phase changes to monoclinic. The morphology of the films grown on both quartz and Si(100) substrates has been studied by scanning electron microscopy and atomic force microscopy. The growth of strongly oriented Sm2O3 on the disordered surface of fused quartz may be interpreted as being driven by the minimization of surface energy.