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The high-power SiC devices require ohmic contact materials, which are prepared by annealing at temperatures lower than 800 °C. Recently, we demonstrated in our previous paper [J. Appl. Phys. 95, 2187 (2004)] that an addition of a small amount of Ge to the conventional binary Ti/Al contacts reduced the ohmic contact formation temperature by about 500 °C, and this ternary contacts yielded a specific contact resistance of approximately 1×10-4 Ω cm2 after annealing at a temperature as low as 600 °C. In this paper, the electrical properties and the microstructures of the Ge/Ti/Al contacts (where a slash “/” indicates the deposition sequence) were investigated by current-voltage measurements and transmission electron microscopy observations, respectively, in order to understand the ohmic contact formation mechanism. Ti3SiC2 compound layers (which were previously observed at the metal/SiC interface in the Ti/Al ohmic contacts after annealing at temperatures higher than 1000 °C) were observed to grow epitaxially on the SiC surface after annealing at temperatures as low as 600 °C. The Ti3SiC2 layers were believed to act as a p-type intermediate semiconductor layer, which played a key role to reduce the Schottky barrier height at the contacting metal/SiC interface. Further reduction of the contact resistances of the Ge/Ti/Al contacts would be achieved by increasing the coverage of the Ti3SiC2 layers on the SiC surface. [ABSTRACT FROM AUTHOR]

Both luminescence properties and dissociation kinetics of Mg-H complex for as-grown Mg-doped GaN are simultaneously investigated by low-energy electron-excited nanoluminescence (LEEN) spectroscopy. Ultraviolet luminescence at 3.2-3.3 eV and blue luminescence at 2.8-2.9 eV are observed as predominant LEEN emissions. In-depth profiles of LEEN emission show that the blue luminescence is the predominant emission for highly Mg-doped GaN. Electron-beam exposure less than 50 mC/cm² produces an increase of the ultraviolet luminescence intensity and reduction of the blue luminescence intensity. These characteristics suggest that the blue luminescence is due to a transition from hydrogen-related deep donor to Mg acceptor and that the ultraviolet luminescence is due to transitions from conduction band and/or shallow hydrogen donor to Mg acceptor. We propose a kinetic model for dissociation reactions of Mg-H complex during electron exposure, and the reaction rate is evaluated to be (3.5±0.3)× 10[sup -3] s[sup -1] for electron beams with 3.1× 10[sup -5] A/cm² at 5.0 keV. [ABSTRACT FROM AUTHOR]

The stabilities of the electrical properties and microstructures of Pt, PtAu, NiAu, and TaTi ohmic contacts after contact formation were studied. The Pt and PtAu contacts annealed in an O[sub 2] and N[sub 2] mixed gas ambient had the specific contact resistance (ρ[sub c]) of high-10[sup -3] Ω cm[sup 2] and strong adhesion to the GaN substrates. The NiAu contact annealed in the partial O[sub 2] ambient had poor adhesion to the GaN, although the ρ[sub c] value of low-10[sup -3] Ω cm[sup 2] was obtained. The TaTi contact had the lowest ρ[sub c] values of less than 10[sup -4] Ω cm[sup 2]. After contact formation, the Pt and NiAu ohmic contacts prepared by annealing in the partial O[sub 2] ambient showed the excellent electrical and microstructural stabilities during room temperature storage and current injection. However, the contact resistance of the TaTi contact prepared by annealing at 800 °C increased during room temperature storage, and the mechanical failure of the contact was also observed after injecting current as low as 4 kA/cm2. From the present experiments, it was concluded that the Pt and PtAu contacts were the most reliable ohmic contact materials for p-GaN among four contact metals. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Part II. Presents transport measurements and materials studies carried out for molybdenum-germanium-indium-tungsten contacts. Importance of thermally stable ohmic contacts for integrated circuits; Role of indium in forming ohmic contacts; Development of a controllable fabrication process to yield thermally stable low-resistance contacts.

Studies the effects of interfacial microstructure on uniformity and thermal stability of gold-nickel-germanium ohmic contact to n-type gallium arsenide. Experimental procedures; Experimental results; Discussion of findings.

Focuses on a study that examined the strain behavior of polycrystalline niobium (Nb) thin films deposited onto oxidized silicon substrates using an electron gun in a high vacuum system. Status of the sign and magnitude of strain in Nb thin films; Factor responsible for the increase in the use of refractory thin films as electrode device materials; Significance of the reduction of strain level in refractory films.

Reports on the development of thermally stable, low-resistance p-type ohmic contacts by depositing NiInW metals on gallium arsenide (GaAs) substrates in which beryllium (Be) and fluorine were coimplanted. Experimental procedures; Be distribution in GaAs; NiInW ohmic contacts.

Presents a study that analyzed the effect of silicon or germanium addition to nitrogen-indium-tungsten ohmic contacts on their electrical behavior. Analysis of the ohmic contacts prepared by two-step anneal; Difference between silicon and germanium addition to the ohmic contacts; Comparison between gold-germanium nitride and nitrogen-indium-tungsten ohmic contacts.

Presents a study that analyzed the electrical properties and microstructure of indium arsenide ohmic contacts to n-type gallium arsenide semiconductors. Measurement of the contact resistance; Comparison of contacts prepared by sputter-deposition and evaporation; Effect of intervening oxide layer on indium arsenide and gallium arsenide interaction.

Presents a study that examined electrical properties and thermal stability of indium/tungsten ohmic contacts in gallium arsenide semiconductors. Analysis of the interfacial microstructure of the semiconductor; Measurement of the contact resistances; Influence of layer thickness on the contact resistances of the semiconductor.

Part IV. Focuses on a study which examined the microstructure of the nickel indium tungsten (NiInW) ohmic contact material by cross-sectional transmission electron microscopy. Materials and procedure; Analysis of the role of nickel in the NiInW contacts; Factors that are important in preparing contacts with large fractional coverage of indium[subx] gallium[sub1-x] arsenide phases; Effect of nickel[sub2] gallium arsenide on native oxide sat the gallium arsenide substrate.

Part V. Focuses on a study which investigated the thermal stability of self-aligned refractory metal semiconductor field effect transistors with silver nickel germanium ohmic contact metallurgy or nickel indium tungsten ohmic contact metallurgy. Materials and procedure; Discussion on the performance of the fabricated devices; Observations on the deterioration of device performance; Cause of deterioration.

Presents information on a study which discussed improvement in thermally stable, low-resistance ohmic contacts to n-type gallium arsenide (GaAs) for germanium indium tungsten and nickel indium tungsten contact metals. Experimental procedures; Contact resistance measurements; Microstructural analysis; Correlation between the contact resistance and the indium(In)GaAs; Carrier transport mechanism for Indium-based ohmic contact.

Focuses on the Schottky barrier heights of a variety of metals contacting to p-ZnSe. Internal photoemission method; Interference of the monochromatic incident light; Hysteresis of the C-V values; Turn-on voltages.

The carrier transport mechanism through the p-diamond/metal interface was studied by measuring specific contact resistances (ρ[sub c]) using a transmission line method for Ti, Mo, and Cr (carbide forming metals) and Pd and Co (carbon soluble metals) metals contacting to the boron-doped polycrystalline diamond films. Schottky barrier heights (φ[sub B]) of around 0.5 eV were measured for the annealed contacts. The present result indicates that formation of thermally stable graphite layers at the diamond/metal interfaces upon annealing would pin the Fermi level of the p-diamond. This model led to the preparation of in situ Ohmic contacts by depositing a thin diamondlike carbon on the p-diamond surface prior to metal deposition, and also to excellent Schottky contacts with breakdown voltages higher than 900 V. The present experiment concluded that the existence of a graphite layer at the diamond/metal interface controlled the electrical properties through the p-diamond/metal interface. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the formation of ohmic contacts to p-type diamond using carbide forming metals. Estimation of the acceptor concentrations; Features of a diamond semiconductor; Techniques used in the study of the applicability of semiconducting diamond films to the electronic devices.

Focuses on the contact resistance (R[subc] measurements and microstructural analysis at the metal/diamond interfaces, which were carried out by depositing a variety of metals on the polycrystalline boron-doped diamonds. Effect of annealing on the R[subc] values of the titanium and molybdenum contacts; Semiconducting properties of diamond; Analysis of the primary current flow path at the metal/diamond interfaces; Reason for the reduction of the R[subc] values after annealing.

Proposes a model for current transport of nickel germanium (NiGe)-based ohmic contacts based on the present electrical measurements and microstructural analysis. Substrates used in the experiments; Atomic distribution normal to gallium arsenide substrate after annealing at elevated temperatures; Improvement of contact resistance and process window of the present NiGe.

Improves the contact properties of nickel germanium contacts by adding another third element. Microstructural analysis of the sample before and after annealing; Isochronal annealing for contact formation; Correlation between thermal stability and microstructure.

Presents information on a study which developed non-gold NiGe Ohmic contacts by a lift-off and annealing technique that was extensively used to fabricate the conventional AuGeNi contacts. Experimental procedures; Ohmic contact formation; Isochronal annealing for contact formation; Correlation between electrical properties and microstructures.

Presents information on a study which located process parameters to develop low resistance and thermally stable NiSiW Ohmic contacts, where the top W layers were used to reduce the contact metal sheet resistance. Experimental procedure; Correlation between electrical properties and microstructural analysis; Comparison between NiSiW contacts and NiGe contacts.

Reduction of annealing temperature to prepare low resistance ohmic contact materials for p-type 4H-SiC was achieved by adding Ge to the conventional TiAl contacts. Although the binary TiAl contact is required to anneal at temperature as high as 1000 °C to convert Schottky to ohmic behavior after deposition of the Ti and Al layers on the SiC substrate, the GeTiAl contacts provided the specific contact resistance of about 1×10[sup -4] Ω cm[sup 2] by annealing at temperature as low as 600 °C. This low annealing temperature is desirable to reduce the gate leakage current of the SiC devices. The GeTiAl ohmic contacts were thermally stable during isothermal annealing at 400 °C subsequently after preparing the ohmic contacts by annealing at 600 °C, which is also required by the device packaging process. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The maximum electrical conductivities in polycrystalline Cu interconnects with sub-100 nm linewidth were extrapolated from the measured resistivities of the Cu interconnects with various linewidths (100–1000 nm) using a Mayadas–Shatzkes (MS) model. These polycrystalline Cu interconnects with TiN cap layers were fabricated by the focused ion beam technique. The scattering parameters by the surface and grain boundary, which were needed to extrapolate the resistivities of the sub-100 nm Cu interconnects (using the MS model), were determined to be zero and 0.5, respectively. The result suggested that the grain boundary scattering primarily increased the resistivity of the polycrystalline Cu interconnects. We concluded that large grained Cu interconnects and ultrathin barrier layers were essential to realize low resistance nano-scale Cu interconnects in the future ultralarge scale integration devices. [ABSTRACT FROM AUTHOR]

The direct quantitative correspondence between theoretical predictions and the measured plasma fluctuations and transport is tested by performing nonlinear gyro-Landau-fluid simulations with the GRYFFIN (or ITG) code [W. Dorland and G. W. Hammett, Phys. Fluids B 5, 812 (1993); M. A. Beer and G. W. Hammett, Phys. Plasmas 3, 4046 (1996)]. In an L-mode reference discharge in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], which has relatively large fluctuations and transport, the turbulence is dominated by ion temperature gradient (ITG) modes. Trapped electron modes and impurity drift waves also play a role. Density fluctuations are measured by beam emission spectroscopy [R. J. Fonck, P. A. Duperrex, and S. F. Paul, Rev. Sci. Instrum. 61, 3487 (1990)]. Experimental fluxes and corresponding diffusivities are analyzed by the TRANSP code [R. J. Hawryluk, in Physics of Plasmas Close to Thermonuclear Conditions, edited by B. Coppi, G. G. Leotta, D. Pfirsch, R. Pozzoli, and E. Sindoni (Pergamon, Oxford, 1980), Vol. 1, p. 19]. The shape of the simulated wave number spectrum is close to the measured one. The simulated ion thermal transport, corrected for E×B low shear, exceeds the experimental value by a factor of 1.5 to 2.0. The simulation overestimates the density fluctuation level by an even larger factor. On the other hand, the simulation underestimates the electron thermal transport, which may be accounted for by modes that are not accessible to the simulation or to the BES measurement. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Effects of Pd or Pt addition to Ti/Al ohmic contact materials used for n-type Al[sub 0.2]Ga[sub 0.8]N grown on the GaN substrates were studied where Si with 2×10[sup 18] cm[sup -3] were doped in the AlGaN layers. The contact metals were prepared by depositing either by the electron-beam or thermal evaporation technique, and then annealed at high temperatures for 30 s in N[sub 2] atmosphere. It was found that the addition of a small amount of Pd or Pt to the Ti/Al ohmic contact materials reduced the contact resistivities of the Ti/Al contacts. The lowest contact resistivity of 4.1×10[sup -6] Ω cm[sup 2] was obtained in the Ti(20 nm)/Pd(5 nm)/Al(200 nm) contact after annealing at 600 °C (where a slash “/” indicates the deposition sequence). The reduction of the contact resistivities by the Pd or Pt addition was believed to be due to increase in the donor concentration in the AlGaN layers by forming Pd–Ga or Pt–Ga compounds in the contact metals after annealing at elevated temperatures. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the effects of a nickel monoxide (NiO) layer on the electrical properties of NiAu-based ohmic contacts for p-gallium arsenide (GaN) by depositing a p-type NiO layer on the p-GaN using a sputter-deposition technique. P-type conduction of NiO layers doped with Li[NiO(Li); Sheet resistivity; Variety of the NiAu-based contacts with the NiO layers.

Develops a thermally stable, low-resistance indium-based NiInW ohmic contact to n-type gallium arsenide by sputter deposition. Composition of the contacts; Observation on the contact resistance and contact morphology; Incorporation of n-type dopants into the metallization.

Reports on thermally stable low-resistance ohmic contacts to n-type gallium arsenide (GaAs) incorporating a very thin layer of gold (Au) in conjunction with a layered nickel/germanium/tungsten (Ni/Ge/W) structure. Need for the beta-AuGa in the formation of low eutectic-based AuGeNi contacts; Resulting contact resistance; Contact stability under thermal stress.

A new thermally stable, low-resistance NiInW contact metal to n-type GaAs has been developed by depositing a thin In layer with Ni and W layers and annealing at elevated temperatures for a short time. Low resistances of ∼0.3 Ω mm were obtained at annealing temperatures in the range of 800 to 1000 °C. The contact resistances were stable during subsequent annealings at 400 °C for 100 h and 500 °C for 10 h. The thermal stability of the contact resistance and the surface morphology of this contact are superior to those of the conventionally used AuNiGe contacts and this new contact is suitable for various device applications. Further reduction of the contact resistance can be achieved simply by reducing the sheet resistance of the contact metals. [ABSTRACT FROM AUTHOR]