Growth of Low Resistivity p-Type 4H-SiC Crystals by Sublimation with Using Aluminum and Nitrogen Co-Doping

Low resistivity p-type SiC bulk crystals were grown by the sublimation method with using aluminum and nitrogen co-doping. In the sublimation growth of 4H-SiC, to obtain low-resistive p-type crystals are not easy because of the instability of 4H-SiC polytype with highly Al-doping. We have grown < 90 mΩcm p-type 4H-SiC bulk crystals with the co-doping condition. The results of SIMS and Raman spectroscopy show that high concentration of nitrogen co-doping could be effective to the stabilization of 4H polytype with p-type SiC growth.

Colossal Permittivity Observed in Yttrium Doped BaTiO3

Colossal permittivity (CP) in BaTiO3(BT)-based polycrystalline ceramics with normal grain sizes has been successfully obtained in yttrium (Y) doped BT ceramics (BYT) via a simple and effective method. Considering the necessary factors for CP formation mechanism, well designed doping condition and sintering procedure were carried out in the sample preparation. Characterizations show that BYT is with a pure tetragonal perovskite structure and the grain growth is depressed under the action of Y donor doping. The frequency independence of permittivity and Debye-like relaxation related to Maxwell-Wagner relaxation which occurred at the interfaces between semiconducting grains and insulating grain boundaries can be detected. These are induced by an internal barrier layer capacitance (IBLC)-type structure which formed under an overall and carefully designed synthesis procedure. But the temperature independence of permittivity does not arise because of the particular tetragonal structure and micron dimension grain sizes of BYT.

Stable Structures of Donor-Acceptor-Donor Trimer Codopants in 4H-SiC

The total energies of 4H-SiC with donor-acceptor-donor (D2A) trimer codopants (D = N, P, As, and Sb, A = B, Al, Ga, and In), the formation energies of D2A, DA, D, and A species and the binding energies were studied usingab initiocalculations in order to determine the stable structures of D2A trimer codopants in 4H-SiC. The results of the calculations indicated that some of the trimer codopants were formed and were stable in 4H-SiC. In particular, N2Al, N2Ga and N2In trimer codopants with N(Ch)-Al/Ga/In (Sik)-N(Ch) configuration and As2B trimer codopants with As (Sih)-B(Ck)-As (Sih) configuration stably exist in 4H-SiC under the doping condition wherein the concentration ratio of donors to acceptors is 2 : 1.

Effect of Doping on Nanowire Morphology during Plasma-assisted Chemical Vapor Deposition

ABSTRACTMorphologies of silicon nanowires grown by plasma-assisted metalorganic chemical vapor deposition were studied in the presence of various dopant precursors. The varied precursors affected the axial and radial growth rates over orders of magnitude where triethylborane showed the strongest enhancements for both axial and radial growth, and triethylarsenic and triethylantimony retarded axial growth. Native oxide thickness is also shown to depend strongly on doping condition resulting in increased oxide thicknesses for increased carrier concentration, using shifts in the measured binding energy of the silicon 2p3/2 state as a proxy for carrier concentration.

Fracture Behavior of Single- and Polycrystalline Silicon Films for MEMS Applications

Fracture behaviors of silicon films were evaluated by microtensile methods. We fabricated two types of specimens using surface micromachining, one for a test device for microtensile testing only and the other for a microtensile-compatible resonating device driven by alternating electrostatic force. The piezoelectric-driven uniaxial stress-strain measurement system was designed to evaluate the mechanical properties of thin films. We used UV adhesive to grip the device to the microtensile system, and the grip was made of UV-transparent glass in order to cure the underlying UV adhesive layer. To assess fracture toughness, we used newly proposed methods combining resonance frequency and microtensile methods. The fracture strength of single- and polycrystalline silicon showed dependence on geometry and doping condition. By varying the geometry, we analyzed the effect of the CMP side and the dry-etched side on changes in the mean fracture strength. Atomic force microscopy observation showed that the larger flaws of the dry-etched side were significant in decreasing the mean fracture strength. Fracture toughness based on fracture mechanics with a precrack was evaluated by newly proposed methods combining resonance frequency and microtensile techniques. The measured toughness was independent of specimen geometry but dependent on doping condition. The measured fracture toughness of notched specimens was 33% higher than that of pre-cracked specimens, even though the notch radius was as small as 1.4µm. The effects of notch-tip radius and doping on fracture toughness of silicon film were also analyzed.

Simulation of Under- and Supersaturation of Gallium Vacancies in Gallium Arsenide During Silicon in- and Outdiffusion

ABSTRACTThe diffusivity of Si in GaAs shows a dependence on the cubic power of its concentration or the concentration of electrons n under both in- and outdiffusion conditions. Hence, the diffusion of Si in GaAs is consistent with the Fermi-level effect model invoking the triply-negatively-charged Ga vacancies, , as the point defect species responsible for diffusion to occur on the Ga sublattice under n-doping condition. However, the Si diffusivity values of the indiffusion cases is several orders of magnitude smaller than those of the outdiffusion cases at the same Si concentrations. This means that the two apparent Si diffusivity values under intrinsic conditions will contain also the same discrepancy, which has been previously assessed to be due to a undersaturation in indiffusion cases and a supersaturation in outdiffusion cases. In this study we have calculated the under- and supersaturation values using the known Si diffusivities. We found that the GaAs surface states play a key role in the development of the under- and supersaturations.