Hiroaki Kariyazaki

A study on density functional theory of the effect of pressure on the formation and migration enthalpies of intrinsic point defects in growing single crystal Si

In 1982, Voronkov presented a model describing point defect behavior during the growth of single crystal Si from a melt and derived an expression to predict if the crystal was vacancy- or self-interstitial-rich. Recently, Vanhellemont claimed that one should take into account the impact of compressive stress introduced by the thermal gradient at the melt/solid interface by considering the hydrostatic pressure dependence of the formation enthalpy of the intrinsic point defects. To evaluate the impact of thermal stress more correctly, the pressure dependence of both the formation enthalpy (Hf) and the migration enthalpy (Hm) of the intrinsic point defects should be taken into account. Furthermore, growing single crystal Si is not under hydrostatic pressure but almost free of external pressure (generally in Ar gas under reduced pressure). In the present paper, the dependence of Hf and Hm on the pressure P, or in other words, the pressure dependence of the formation energy (Ef) and the relaxation volume (vf),...

Crystal Structure of New Carbon–Nitride-Related Material C2N2(CH2)

A new carbon–nitride-related C2N2(CH2) nanoplatelet was synthesized by subjecting a precursor C3N4HxOy nanoparticle in a laser-heating diamond anvil cell to the pressure of 40 GPa and temperature of 1200–2000 K. The C and N composition of the quenched sample was determined to be C3N2 by using an energy dispersive X-ray spectroscope attached to a transmission electron microscope. The crystal structure and atomic positions of this C3N2 were obtained through Rietveld analysis of the X-ray diffraction pattern measured using synchrotron radiation. The hydrogen composition was difficult to determine experimentally because of the several-hundred-nanometer dimensions of the sample. First-principles calculation was alternatively used to discover the hydrogen composition. The synthesized C2N2(CH2) was accordingly found to be an orthorhombic unit cell of the space group Cmc21 with lattice constants a = 7.625 A, b = 4.490 A, and c = 4.047 A. If the CH2 atomic unit is replaced with the CN2 atomic unit and the bonding rearranged, the C2N2(CH2) becomes the expected superhard C3N4.

Electronic structure of C2N2X (X = O, NH, CH2): Wide band gap semiconductors

The electronic structure of IV2V2VI class semiconductors, C2N2X (X = O, NH, CH2), was investigated using first principles calculations. The crystal structures of C2N2X are isostructural with the Si2N2O compound, sinoite. The valence of the X atom is virtually two, and thus the substitution of X (X = O, NH, CH2) is isoelectronic. From the calculated density of states, the carbon 2 p orbital does not participate in the upper valence band (VB) (0 to –5 eV). The upper valence band is dominated by the N 2 p and X 2 p orbitals. The calculated optical absorption edge shifts to a lower energy as the substitution progresses from the O atom to the CH2 group. The calculated absorption edge is 7.76, 7.07, and 6.66 eV for C2N2O, C2N2(NH), and C2N2(CH2), respectively.

Bond strengths of New Carbon-nitride-Related material C2N2(CH2)

A new carbon-nitride-related material C2N2(CH2) nanopletelet was synthesized by subjecting a precursor C3N4HxOy+Au in a laser-heating diamond anvil cell (LHDAC) to the pressure of 40 GPa and the temperature of 1200-2000 K. The synthesized C2N2(CH2) was accordingly found to be an orthorhombic unit cell of the space group Cmc21 with lattice constants a = 7.625A, b = 4.490A, and c = 4.047A. The bulk modulus B0 was determined to be B0 = 258 ± 3.4 GPa, only the 60 % that of the diamond. C2N2(CH2) consists of the tetrahedrally coordinated C with three C-N single bond and the one C-C single bond, and the bridging carbon with the C-CH2-C bond. The C-N single bond length of the tetrahedron ranges from 1.444 to 1.503 A. This bond length is close to the C-N single bond of 1.447 to 1.458 A in the superhard β-C3N4. The compressibility of the C-N and C-C single bond of C2N2(CH2) ranges from 0.976 to 0.982 with the pressure of 30 GPa. These values are very close to the compressibility of the C-N and C-C single bond of 0.978 to 0.982 in β-C3N4, cubic-C3N4, and diamond.

Molecular simulation on interfacial structure and gettering efficiency of direct silicon bonded (110)/(100) substrates

Direct silicon bonded (DSB) substrates with (110)/(100) hybrid orientation technology are attracting considerable attention as a promising technology for high performance bulk complementary metal-oxide semiconductor technology. We have investigated the structure and the gettering efficiency of the (110)/(100) interface parallelling each ⟨110⟩ direction (DSB interface) by molecular dynamics (MD) and first-principles calculation. In MD calculations, initial calculation cells of 15 atomic-configurations with coincidence-site lattices were prepared. It was found that (i) the calculated DSB interface was stable independent of the initial atomic-configurations and (ii) the interfacial structures were essentially the same among the calculated models. Moreover, the calculated interfacial structure corresponds to the reported TEM observation. The first-principles calculation showed that Si atoms in the DSB interface formed covalent bonding. The dangling bonds in Si (110) and (100) surfaces disappeared due to restr...

Gettering Efficiency of Si(110)/Si(100) Directly Bonded Hybrid Crystal Orientation Substrates

Si(110) and Si(100) directly bonded (DSB) substrates are paid attention as candidate materials for the substrate of next-generation complementary metal oxide semiconductors (CMOSs). From a practical viewpoint on DSB substrates, we have investigated the gettering efficiency at the bonded interfaces of DSB substrates. In our experiments, DSB substrates were intentionally contaminated with 3d transition metals (Fe, Cu, and Ni) and then annealed at 1000 °C. The dependence of the concentrations of these metals on the depth of what was evaluated by secondary ionization mass spectrometry (SIMS). It was found that the bonded interface has a good gettering ability for these metals. Results of the preferential etching method support the results of SIMS. Transmission electron microscopy (TEM) showed that (i) the gettered Fe and Ni formed the silicides FeSi2 and Ni2Si3, respectively; however, (ii) no Cu precipitates formed at the bonded interface. Furthermore, we confirmed that the bonded interface can be effective gettering sites for Cr and Ti. This result indicates that the bonded interface can become effective gettering sites for metals with low diffusivities, if they reach the interface just below the device active layer.

Bulk modulus and structural changes of carbon nitride C2N2(CH2) under pressure: The strength of C–N single bond

The experimental bulk modulus, B0, of C2N2(CH2) is determined to be 258 ± 3.4 GPa from the analysis of high-pressure (up to 30 GPa) X-ray diffraction patterns obtained using synchrotron radiation. This bulk modulus is 40% lower than that of diamond. At the level of a combined analysis of lattice constants determined experimentally and atomic positions obtained theoretically for the compression behavior of C2N2(CH2), the strength of the C–N single bond is determined to be the same as the C–C single bond in diamond. In other words, the tetrahedral frame of C2N2(CH2) which consists of CN3Cb, where Cb is a bridging carbon, is as hard as diamond. To account for the differing bulk moduli, we infer that the lower bulk modulus in C2N2(CH2) is due to the rotational freedom in the crystal at high pressures.

Gettering Efficiency of Si (110)/(100) Directly Bonded Hybrid Crystal Orientation Substrates

We have investigated the gettering efficiency at the interface of Si (110) and Si (100) directly bonded (DSB) substrates. DSB substrates were prepared by conventional bonding and grinding back methods. DSB substrates were intentionally contaminated with 3d transition metals (Fe, Ni, Cu) and then annealed at 1000 oC. The dependence of metal concentrations on the depth was evaluated by a secondary ionization mass spectrometer (SIMS). Furthermore, we observed the interface of DSB by transmission electron microscope (TEM), and characterized the form of the gettered metals.

Molecular simulation on interfacial structure and gettering efficiency of Si (110)/(100) directly bonded hybrid crystal orientation substrates

Hybrid crystal orientation technology (HOT) substrates comprised of Si (100) and (110) surface orientation paralleling each <110> direction attract considerable attentions as one of the promising technology for high performance bulk CMOS technology. Although HOT substrates are fabricated by wafer bonding of Si (110) and Si (100) surfaces, it is not clear the atomic configuration of interfacial structure. Furthermore, the possibility for the interface to be an effective gettering source of impurity metals was not well studied. In this paper, we studied the interfacial structure and gettering efficiency of the atomic bonded interface by molecular simulations. The results indicate that the simulated atomic configuration and gettering efficiency of the bonded interface agreed well with the experimental results.