bluuebunny/crossref_metadata_2025_split huggingface dataset:
Localized Doping Enhancement by Photon-Assisted Chemical Beam Epitaxy
Authors: Shi B.Q. , Tu C.W. 
Published: April 2011

ABSTRACTDoping results from Ar+-laser-assisted chemical beam epitaxy with triethylgallium, tris(dimethylamino) arsenic and silicon tetrabromide as group-HI, group-V and dopant precursors respectively are reported. Enhancements in the n-type doping concentration are observed with laser irradiation in the investigated substrate-temperature range 390°C – 500°C. With a 300 W/cm2 irradiation power density, an increase in the carrier concentration by 70 times is obtained at 390°C substrate temperature. A numerical model developed by us for epitaxial growth and doping with the above precursors is used to assess the contribution of laser-induced thermal heating to the observed doping increase. A reaction scheme for photo-induced decomposition of physisorbed silicon tetrabromide is proposed. A kinetic rate equation for the photolysis is derived and used to estimate the absorption cross section required to reproduce the observed concentration enhancements resulted from laser irradiation. The possibility is established that dramatic increases in carrier concentration at low growth temperatures are due to photolysis of physisorbed silicon tetrabromide.
Self-Consistent Rate-Equation Approach to Nucleation and Growth in Point/Extended Island Models of 1-D Homoepitaxy
Authors: Amar Jacques G. , Popescu Mihail N. , Family Fereydoon 
Published: April 2011

ABSTRACTA self-consistent rate equation (RE) approach to submonolayer growth on a one-dimensional surface is presented. This approach explicitly takes into account the existence of gaps between clusters and can successfully predict the coverage dependence of the average densities of monomers N1, and clusters, N. It also implies an unusual dependence for the monomer-monomer capture number σ1 as a function of monomer density. To obtain the island size-distribution, a second set of mean-field equations is used describing the evolution of the size-dependent capture zones and leading to explicit size- and coverage-dependent capture numbers. The solution of this fully self-consistent RE approach is then compared with kinetic Monte Carlo results
Lateral InxGa1−x, P Heterostructures Obtained by Single Step Growth on Pre-Patterned Substrate by Chemical Beam Epitaxy
Authors: de Castro M.P.P. , Betitni J. , Ribeiro C.A. , Carvalho M.M. , Frateschi N.C. 
Published: April 2011

ABSTRACTWe present an investigation on the spatial compositional variation in InGaP layers grown by chemical beam epitaxy (CBE) on pre-patterned substrates. Neighboring regions with 190 meV bandgap discontinuity are observed with the growth at 500°C. The development of laser structures on V-grooves that incorporate these lateral heterostructures is achieved by controlling the growth temperature during growth
A Kinetic Monte Carlo Model for Ga Desorption from Chemisorbed and Physisorbed States During High Temperature GaAs MBE
Authors: Mahalingam K. , Dorsey D. L. , Taferner W. T. , Eyink K. G. 
Published: April 2011

ABSTRACTA kinetic Monte Carlo model is developed to examine the influence of As/Ga flux ratio on the Ga desorption kinetics during molecular beam epitaxy of (100)-GaAs, based on data reported in desorption mass spectrometry experiments. A good match to experimental results is obtained when a mechanism involving desorption from a physisorbed state is included, in addition to desorption from a chemisorbed state. Analysis of the results revealed that the dependence of the Ga desorption energy on the As/Ga flux ratio, observed in growth experiments, is explained in terms of the component due to desorption from the physisorbed state. The Ga desorption energy associated with the chemisorbed state is independent of the As/Ga flux ratio. These predictions are similar to results reported in a recent study of In desorption during molecular beam epitaxy of InGaAs
Elevated Temperature Silicon Carbide Chemical Sensors
Authors: George M. A. , Ayoub M. A. , Ila D. , Larkin D. J. 
Published: April 2011

ABSTRACTIn this study, the (I-V) properties of the sensors were measured as a function of hydrogen, propylene and methane exposure at temperatures up to 400° C and sensor responses were observed for each gas. The response to hydrogen and propylene had a rapid increase and leveling off of the current followed by the subsequent decrease to the baseline when the gas was switched off. However, exposure to methane resulted in a rapid spike in the current followed by a gradual increase with continued exposure. X-ray photoelectron (XPS) studies of methane exposed SiC sensors revealed that this behavior is attributed to the oxidation of methane at the Pd surface.
Characterization of Thick 4H-SiC Hot-Wall CVD Layers
Authors: Paisley M. J. , Irvine K. G. , Kordina O. , Singh R. , Palmour J. W. , Carter C. H. 
Published: April 2011

ABSTRACTEpitaxial 4H-SiC layers suitable for high power devices have been grown in a hot-wall chemical-vapor deposition (CVD) system. These layers were subsequently characterized for many parameters important in device development and production. The uniformity of both thickness and doping will be presented.Doping trends vs. temperature and growth rate will be shown for the p-type dopant used. The n-type dopant drops in concentration with increasing temperature or increasing growth rate. In contrast, the p-type dopant increases in concentration with decreasing temperature or increasing growth rate. A simple descriptive model for this behavior will be presented.The outcome from capacitance-voltage and SIMS measurements demonstrate that transitions from n to n−, or p to p−, and even n to p levels can be made quickly without adjustment to growth conditions. The ability to produce sharp transitions without process changes avoids degrading the resulting surface morphology or repeatability of the process. Avoiding process changes is particularly important in growth of thick layers since surface roughness tends to increase with layer thickness.Device results from diodes producing two different blocking voltages in excess of 5 kV will also be shown. The higher voltage diodes exhibited a breakdown behavior which was near the theoretical limit for the epitaxial layer thickness and doping level grown.
Homo-Epitaxial and Selective Area Growth of 4H and 6H Silicon Carbide Using a Resistively Heated Vertical Reactor
Authors: Eshun Ebenezer , Taylor Crawford , Spencer M. G. , Kornegay Kevin , Ferguson Ian , Gurray Alex , Stall Rick 
Published: April 2011

ABSTRACTSilicon carbide technology is rapidly developing into a production process. This is due to rapid progress in the development of high quality epitaxy and substrates. We report on the development of a resistively heated vertical reactor and it's application to homo-epitaxy and selective area growth. Epitaxial growth of 4H and 6H-SiC requires high temperatures (in excess of 1500°C). In this work we investigate resistive heating which offers advantages in cost, temperature uniformity and power efficiency of heating. However, resistive heating presents major technological challenges. Due to the power efficiencies possible with resistive heating we are able to obtain temperatures in excess of 1750°C. Using this system we have grown “state of the art” 4H and 6H-SiC. At 1580°C our background doping is p-type at a level of 3–5×1015cm−3 as measured by capacitance techniques in agreement with earlier results presented by investigators from Siemens Corp using a similar system. The background concentration increases by about an order of magnitude at 1680°C. This system has also been used to perform experiments with selective area growth of SiC using a graphite mask. This masking technology allows for the growth of SiC in specific regions at elevated temperature in excess of 1600°C.
Experimental and Theoretical Analysis of the Hall-Mobility in N-Type Bulk 6H- and 4H-SiC
Authors: Müller S. T. G. , Hofmann D. , Winnacker A. 
Published: April 2011

ABSTRACTThe electrical properties of nitrogen doped n-type 6H- and 4H-SiC bulk crystals grown by the Lely- or modified Lely-method have been characterized by Hall-measurements. The doping densities were determined by a fit of the neutrality equation to the experimental data, accounting for in-equivalent lattice sites and the temperature dependence of the effective density-of- states-mass extracted from recent results of ab-initio-calculations of the 6H- and 4H-SiC bandstructure [1]. The theoretical analysis of the Hall-mobility is based on an extended form of the Rode-Nag iteration algorithm [2]. The calculation scheme considers all relevant elastic and inelastic scattering mechanisms. the anisotropy of the crystal modifications and the possible effect of spatial inhomogeneities in the distribution of donors, acceptors or in the related electron system. Within these concepts it is possible to achieve a quantitative agreement between theoretical and experimental mobility data in 4H- and 6H-SiC over the whole temperature range of band conduction. New values for the acoustic deformation potentials Eac [15.0±0.5 eV (6H), 14.8±0.5 eV (4H)] and the coupling constants for intervalley phonon scattering Dint [2.3 ± 0.1 × 109eV/cm (6H), 2.6 ± 0.1 × 109eV/cm (4H)] are given.
Effect of N/Ga Flux Ratio in GaN Buffer Layer Growth by MBE on (0001) Sapphire on Defect Formation in the GaN Main Layer
Authors: Ruvimov S. , Liliental-Weber Z. , Washburn J. , Kim Y. , Sudhir G. S. , Krueger J. , Weber E. R. 
Published: April 2011

ABSTRACTTransmission electron microscopy was employed to study the effect of N/Ga flux ratio in the growth of GaN buffer layers on the structure of GaN epitaxial layers grown by molecular-beamepitaxy (MBE) on sapphire. The dislocation density in GaN layers was found to increase from 1×1010 to 6×1010 cm−2 with increase of the nitrogen flux from 5 to 35 sccm during the growth of the GaN buffer layer with otherwise the same growth conditions. All GaN layers were found to contain inversion domain boundaries (IDBs) originated at the interface with sapphire and propagated up to the layer surface. Formation of IDBs was often associated with specific defects at the interface with the substrate. Dislocation generation and annihilation were shown to be mainly growth-related processes and, hence, can be controlled by the growth conditions, especially during the first growth stages. The decrease of electron Hall mobility and the simultaneous increase of the intensity of “green” luminescence with increasing dislocation density suggest that dislocation-related deep levels are created in the bandgap.
Reproducibility and Uniformity of MOVPE Planetary Reactors® for the Growth of GaN Based Materials
Authors: Heuken M. , Protzmann H. , Schoen O. , Luenenbuerger M. , Juergensen H. , Bremser M. , Woelk E. 
Published: April 2011

ABSTRACTProduction scale MOVPE reactors such as the AIXTRON 2000HT Planetary Reactor® offer unique possibilities to fabricate highly efficient GaN based devices at a low cost of ownership. The scope of this investigation is to understand the dependence of wavelength, thickness and doping uniformity on parameters such as total gas flow, temperature distribution in the reactor and purity of the precursors. Wafer to wafer uniformity in the 7×2” wafer configuration as well as run to run reproducibility will be discussed. We obtained a wafer to wafer standard deviation of 2.7% for the sheet resistance of Si-doped GaN/InGaN/GaN double heterostructures. The wafer to wafer standard deviation of the main PL emission wavelength at 412.3 nm is 1.8 nm. The run to run reproducibility of the main emission wavelength is <3 nm. We obtained reproducible resistivities of GaN:Mg layers of less than 1 Ωcm which corresponds to 5−10×1017cm−3. Statistical data of p-type doping taking 20 runs into account gave an average hole concentration of 5.5×1017cm−3. Together with the wafer to wafer thickness uniformity of <1% the most sensitive layer properties are well controlled to allow a cost-effective mass production process. Structures such as SQW and MQW structures were grown to understand the performance of a production system with respect to interface properties.
The Effects of Damage on Hydrogen-Implant-Induced Thin-Film Separation from Bulk Silicon Carbide
Authors: Gregory R. B. , Holland O. W. , Thomas D. K. , Wetteroth T. A. , Wilson S. R. 
Published: April 2011

ABSTRACTExfoliation of SiC by hydrogen implantation and subsequent annealing forms the basis for a thin-film separation process which. when combined with hydrophilic wafer bonding, can be exploited to produce silicon-carbide-on-insulator, SiCOI. SiC thin films produced by this process exhibit unacceptably high resistivity because defects generated by the implant neutralize electrical carriers. Separation occurs because of chemical interaction of hydrogen with dangling bonds within microvoids created by the implant, and physical stresses due to gas-pressure effects during post-implant anneal. Experimental results show that exfoliation of SiC is dependent upon the concentration of implanted hydrogen, but the damage generated by the implant approaches a point when exfoliation is, in fact, retarded. This is attributed to excessive damage at the projected range of the implant which inhibits physical processes of implantinduced cleaving. Damage is controlled independently of hydrogen dosage by elevating the temperature of the SiC during implant in order to promote dynamic annealing. The resulting decrease in damage is thought to promote growth of micro-cracks which form a continuous cleave. Channeled H_ implantation enhances the cleaving process while simultaneously minimizing residual damage within the separated film. It is shown that high-temperature irradiation and channeling each reduces the hydrogen fluence required to affect separation of a thin film and results in a lower concentration of defects. This increases the potential for producing SiCOI which is sufficiently free of defects and, thus, more easily electrically activated.
Conducting (Si-Doped) Aluminum Nitride Epitaxial Films Grown by Molecular Beam Epitaxy
Authors: Kim J. G. , Moorthy Madhu , Park R. M. 
Published: April 2011

ABSTRACTAs a member of the III-V nitride semiconductor family, AlN, which has a direct energygap of 6.2eV, has received much attention as a promising material for many applications. However, despite the promising attributes of AlN for various semiconductor devices, research on AlN has been limited and n-type conducting AlN has not been reported. The objective of this research was to understand the factors impacting the conductivity of AlN and to control the conductivity of this material through intentional doping. Prior to the intentional doping study, growth of undoped AlN epilayers was investigated. Through careful selection of substrate preparation methods and growth parameters, relatively low-temperature molecular beam epitaxial growth of AlN films was established which resulted in insulating material. Intentional Si doping during epilayer growth was found to result in conducting films under specific growth conditions. Above a growth temperature of 900°C, AlN films were insulating, however, below a growth temperature of 900°C, the AlN films were conducting. The magnitude of the conductivity and the growth temperature range over which conducting AlN films could be grown were strongly influenced by the presence of a Ga flux during growth. For instance, conducting, Si-doped, AlN films were grown at a growth temperature of 940°C in the presence of a Ga flux while the films were insulating when grown in the absence of a Ga flux at this particular growth temperature. Also, by appropriate selection of the growth parameters, epilayers with n-type conductivity values as large as 0.2 Ω−1 cm−1 for AlN and 17 Ω−1cm−1 for Al0.75Ga0.25N were grown in this work for the first time.
Fast and Slow UV-Photoresponse in n-Type GaN
Authors: Rocha R. , Koynov S. , Brogueira P. , Schwarz R. , Chu V. , Topf M. , Meister D. , Meyer B. K. 
Published: April 2011

ABSTRACTThe photocurrent decay in n-type GaN films prepared by low-pressure chemical vapor deposition (LPCVD) was measured in the ms-to-s time range using steady-state UV light and in the μs time regime using short high-power pulses from higher harmonics of a Nd:YAG laser. A power law time dependence is observed with exponents ranging from −0.1 to −0.3, which is an indication of a broad distribution of trapping states inside the band gap. Combining Hall effect results and the magnitude of the initial slope of the photocurrent decay we estimate a mobility-lifetime product of 2.1×10−4 cm2/V for photogenerated electrons at times below a few μs. Slow transients might be a handicap for applications of GaN in UV detectors.
High Voltage P-N Junction Diodes in Silicon Carbide Using Field Plate Edge Termination
Authors: Chilukuri R. K. , Ananthanarayanan P. , Nagapudi V. , Baliga B. J. 
Published: April 2011

ABSTRACTIn this paper, we report the successful use of field plates as planar edge terminations for P+-N as well as N+-P planar ion implanted junction diodes on 6H- and 4H-SiC. Process splits were done to vary the dielectric material (SiO2 vs. Si3N4), the N-type implant (nitrogen vs. phosphorous), the P-type implant (aluminum vs. boron), and the post-implantation anneal temperature. The nitrogen implanted diodes on 4H-SiC with field plates using SiO2 as the dielectric, exhibited a breakdown voltage of 1100 V, which is the highest ever reported measured breakdown voltage for any planar ion implanted junction diode and is nearly 70% of the ideal breakdown voltage. The reverse leakage current of this diode was less than 1×10−5 A/cm2 even at breakdown. The unterminated nitrogen implanted diodes blocked lower voltages (∼840V). In contrast, the unterminated aluminum implanted diodes exhibited higher breakdown voltages (∼80OV) than the terminated diodes (∼275V). This is attributed to formation of a high resistivity layer at the surface near the edges of the diode by the P-type ion implant, acting as a junction termination extension. Diodes on 4H-SiC showed higher breakdown than those on 6H-SiC. Breakdown voltages were independent of temperature in the range of 25 °C to 150 °C, while the leakage currents increased slowly with temperature, indicating surface dominated components.
Electrical and Optical Study of Charge Traps at Passivated GaAs Surfaces
Authors: Mochizuki Yasunori 
Published: April 2011

ABSTRACTPerformance of GaAs-based FETs is strongly affected by the electrical properties of passivated surfaces via the surface charges induced at interface states and at the traps within the passivation films. In order to study these two kinds of sources, a set of new characterization techniques are respectively developed for the GaAs interface system, which is in a largely different situation from that for the SiO2/Si interfaces. Our optical technique based on electroreflectance allows accurate evaluation of interface states and is especially useful for the material systems with strong surface pinning. For the study of trapping centers in CVD dielectrics, use of thermally oxidized Si interfaces is found to be quite convenient. The experimental findings are further discussed in conjunction with FET characteristics and an importance of time-domain control of the surface charges is emphasized in the power FET operation. This concept turns out to be the main motivation of a new MESFET structure with a filed-modulating plate (FPFET) which has achieved a state-of-the-art RF performance based on GaAs.
DX Center Energy Level in InxAl1−xAs Compounds
Authors: Sari Hüseyin , wieder Harry H. 
Published: April 2011

ABSTRACTThe presence of DX centers in InxAl1−xAs, primarily in the indirect portion of the InxAl1−xAs bandgap, has been determined using modulation doped InxAl1−xAs/InyGa1−yAs heterostructures by means of persistent photoconductivity (PPC) and galvanomagnetic measurements. From the cooling bias experiment, the PPC, and self consistent Poisson and Schrddinger simulations the ratio of the ionized shallow donors to the DX centers is obtained. Using this ratio in the grand canonical ensemble (GCE) the energy level of DX centers is determined. It is found that the DX energy level merges with the conduction band at x ≅ 0.42 and is resonant with the conduction band in higher indium concentration.
Si1−xGexOxidation by Plasma Assisted Processing: Oxide Uniformity and Electrical Properties
Authors: Busani T. , Plantier H. , Devine R. A. B. , Hernandez C. , Campidelli Y. 
Published: April 2011

ABSTRACTAnodic oxides of SixGe1−x(0 ≤ x ≤ 1 ) alloys have been made by plasma assisted oxidation in a microwave frequency (2.45 GHz) reactor working in the constant current bias mode. Oxide films ∼15 – 40 nm (depending upon the Ge concentration) were obtained in 10 minutes without a temperature rise of the substrate of more than 100 °C. Detailed infrared absorption studies of the oxides enabled the Si-O-Si, Ge-O-Ge and Si-O-Ge vibrational modes to be identified, the strongest being at 1056, 858 and 1000 cm−1respectively. These modes are associated with the O asymmetric stretch, their values are at lower wavenumbers than in bulk oxides due partly to ultraviolet radiation induced structural modification and partly to thin film optic effects. A statistical model for the different bonds present in SixGe1−xO2, when used to simulate the infrared spectrum does not predict the experimentally observed form, the Ge-O-Ge peak is in general too intense in the experimental spectrum. Auger electron spectroscopy profiling of the SixGe1−xoxides suggests that there is a build-up of Ge close to the surface/oxide interface so that when combined with the infrared data, we conclude that there is a GeO2rich region at the surface/oxide interface. The oxide is, however, globally stoichiometric. Electrical measurements (C(V) and interface state density) were begun on metal-oxide-semiconductor (MOS) capacitors for Si1−xGex. oxides over the range of concentrations 0 ≤ x ≤ 1. Only Si1−xGexoxides with x≤0.15 appear to yield satisfactory MOS capacitor curves.
Modeling of Surface Manipulation by Femtosecond Laser Pulses
Authors: Gruzdeva A. S. , Gruzdev V. E. 
Published: April 2011

ABSTRACTThere are discussed some fundamental physical aspects of surface manipulation by femtosecond laser pulses. Among touched on problems are formation processes of shock electromagnetic waves and surface ripple structures. Proposed theoretical model of femtosecond laser-pulse interaction with matter is illustrated by results of FDTD modeling of linear and nonlinear light scattering by rough surface. Possibility of surface roughness modification and required for that optimal laser-pulse parameters are discussed on the bases of obtained results.
Novel in-situ Ion Bombardment Process for A Thermally Stable (> 800 °C) Plasma Deposited Dielectric
Authors: Ren F. , Lothian J. R. , Pearton S. J. , Wilson R. G. , LaRoche J. R. , Lee J. W. , Johnson D. , Zavada J. M. 
Published: April 2011

ABSTRACTWe demonstrated an in-situ dielectric film passivation technique by dividing a thick film deposition into many thin film (<40Å) depositions and incorporating the ion bombardment between the depositions. N2 was used for the plasma treatment to passivate the SiNx film and a well passivated and thermally stable SiNx was achieved with this process. The refractive index of N2 treated SiNx film only changed 0.3% when the SiNx film was heated up to 1000 °C and the film with a continuous deposition showed a 2.5% change. From the results of SIMS analysis, the N2 treated SiNx film showed a excellent thermal stability after heat up to 1000 °C. The etch rates of passivated SiNx film in BOE and diluted HF are ≤40 Å/min which is much slower than that of un-treated SiNx (135 Å/min).