Hajime Tomokage

Direct observation of electron emission site on boron-doped polycrystalline diamond thin films using an ultra-high-vacuum scanning tunneling microscope

Surface morphology characteristics and electron emission properties of boron-doped polycrystalline diamond thin films grown by microwave plasma-assisted chemical-vapor deposition were investigated using an ultra-high-vacuum scanning tunneling microscope. Small secondary grains with average size less than 10 nm were observed to be on top of the isolated crystal surfaces. The current imaging tunneling spectroscopy (CITS) study revealed that high electron emission occurred at some crystalline facets while others showed relatively no measurable electron emission. The CITS study at high magnification also indicated that the electron emission was initiated at the grain boundaries rather than at the top of the grains. This observation suggests that the electrons transport through the grain-boundary conductive channels and preferentially emit at the low electron affinity facets.

The field emission properties of silicon carbide whiskers grown by CVD

Abstract Silicon carbide whiskers and films were grown by chemical vapor deposition without a metallic catalyst in the temperature range between 1000 °C and 1150 °C, and at a constant pressure and input gas ratio[H 2 /MTS(Methyltrichlorosilane)] of 5 Torr and 30, respectively. The mean diameter of whiskers increased from 96 nm to 1.24 μm as the deposition temperature increased up to 1100 °C. Further increasing of the growth temperature made the growth mechanism transfer from whisker growth to film growth and the surface morphology adopted a pebble-like structure. Silicon carbide whiskers and films showed cold field emission properties and the whiskers, which were obtained, at a temperature of 1050 °C showed relatively good field emission properties.

Influence of melt-temperature fluctuations on striation formation in large-scale Czochralski Si growth systems

The effects of melt-temperature fluctuations on growth striations in crystals grown in a commercial-scale growth system were studied by an analysis of the fast-Fourier-transform (FFT) method applied to the melt-temperature fluctuations and to the growth striations as evaluated by X-ray topography and spreading-resistance (SR) methods. The period of the growth striations observed in crystals corresponded exactly to that of temperature fluctuations in the melt; however, the amplitude of these growth striations decreased when temperature fluctuations with a constant amplitude occurred rapidly. This phenomenon results from a delay in the response of the microscopic growth rate to rapid temperature fluctuations. The amplitude of melt-temperature fluctuations and the peak height of the FFT power spectra were observed to decrease in the radial direction toward the crystal center, and this trend was also observed for growth striations. It was concluded that temporal thermal fluctuations caused by melt convection are preserved in growth striations for crystals grown in large growth systems.

Fabrication of a single layer graphene by copper intercalation on a SiC(0001) surface

Cu atoms deposited on a zero layer graphene grown on a SiC(0001) substrate, intercalate between the zero layer graphene and the SiC substrate after the thermal annealing above 600 °C, forming a Cu-intercalated single layer graphene. On the Cu-intercalated single layer graphene, a graphene lattice with superstructure due to moire pattern is observed by scanning tunneling microscopy, and specific linear dispersion at the K¯ point as well as a characteristic peak in a C1s core level spectrum, which is originated from a free-standing graphene, is confirmed by photoemission spectroscopy. The Cu-intercalated single layer graphene is found to be n-doped.

Note on the Analysis of DLTS and C2-DLTS

The difference in the peak temperatures of DLTS and C2-DLTS is discussed with reference to the measurement of deep levels in semiconductors. The emission rate of a trap level can be accurately determined when the peak temperature observed in DLTS agrees with that in C2-DLTS. When the peak temperatures disagree, the trap depth and trap density cannot be determined correctly, and the junction profile and trap density have a great effect on the peak temperatures of DLTS and C2-DLTS. These phenomena appear in DLTS and C2-DLTS measurements on Au-doped Si p+n diodes. It is necessary to use C2-DLTS together with DLTS in the study of deep impurities in semiconductors.

Surface resistance and field emission current measurements on chemically vapour deposited polycrystalline diamond measured by scanning probe methods

Scanning tunnelling microscopy (STM) and current imaging tunnelling current spectroscopy (CITS) methods were performed on polycrystalline diamond films grown on silicon substrates grown by microwave plasma-enhanced chemical vapour deposition. Large tunnelling currents were observed at some grain boundaries and crystal surfaces with secondary grains. Following atomic force microscopy (AFM) measurements, we performed scanning probe contact current (SPCC) measurements to investigate the spatial variation of electrical resistance on the surface by using an AFM cantilever in contact mode. The conducting grain boundaries and facets were observed on both boron-doped and undoped samples. For microscale characterization of the field emission properties, we performed scanning probe field emission current (SPFEC) measurements. From the results of STM/CITS, AFM/SPCC and SPFEC, it is concluded that the specific grain boundaries and facets on polycrystalline diamonds work as initial points of electron emission and cause high field emission current through a conducting pass formed in the bulk.

Evaluation of Stress Effects on Electrical Characteristics of N-Type MOSFETs: Variations of DC Characteristics During the Resin-Molding Process

Stress-induced changes in the electrical characteristics of a semiconductor device become a major concern in the production of semiconductor packages because the electrical characteristics are adversely affected by packaging (residual) stresses. The objective of our project is to evaluate the effects of stress on semiconductor devices. In this study, the shift of the DC characteristics of nMOSFETs during the resin-molding process was investigated experimentally. After a silicon chip including the n-type metal oxide semiconductor field effect transistors (nMOSFETs) was encapsulated in a quad flat package, the drain current variations and the transconductance shifts were measured. The drain current decreased during the resin-molding process while no significant shift in threshold voltage was observed. The experimental results were estimated adequately from the residual stress predicted by numerical and experimental analyses and from the stress-sensitivity of the nMOSFETs measured by the four-point bending method. Also, we tested the validity of an electron-mobility model that included the effect of stress. The electron-mobility model takes into account the variation in the relative occupancy of the electrons in each conduction-band energy valley. It was found that the effect of biaxial stress on the variation in electron-mobility can be qualitatively evaluated by the electron-mobility model but are quantitatively different from the experimental results. Several needed improvements to the electron-mobility model are proposed in this article.

Experimental Study of Uniaxial-Stress Effects on DC Characteristics of nMOSFETs

Stress-induced shifts of the direct current characteristics on n-type metal oxide semiconductor field effect transistors (nMOSFETs) were investigated experimentally. The stress sensitivities of nMOSFET characteristics were measured by the 4-point bending method, and the gate-length dependence of transconductance shifts caused by uniaxial stress was evaluated. As a result, it is shown that the gate-length dependence of transconductance shifts is attributed to parasitic resistance of the nMOSFETs. Also, this paper verified the electron-mobility model proposed in the previous study that includes stress effects in comparison with the experimental results. As a result, several improvements for the electron-mobility model are proposed in this paper. We describe the change of the conduction-band energy induced by the shear deformation of silicon. The shear deformation with a uniaxial stress along the direction of silicon should be considered in the change of the conduction-band energy.

Influence of uniaxial mechanical stress on the high frequency performance of metal-oxide-semiconductor field effect transistors on (100) Si wafer

The effects of uniaxial mechanical stress on the radio frequency performance of n- and p-metal-oxide-semiconductor field effect transistors (MOSFETs) are investigated up to 10 GHz. Under tensile stress, the gate transconductance (gm) increases in the n-MOSFETs while it decreases in the p-MOSFETs, whereas the results were vice versa for compressive stress. The total gate capacitance (CG) extracted from scattering parameters increases (decreases) under tensile (compressive) stress for both n- and p-MOSFETs, which is explained by the variation in the effective mass perpendicular to the Si/SiO2 interface. The cut-off frequency (fT) varies in inverse proportion to the CG variation.

Annealing of supersaturated low-temperature substitutional gold in silicon

An annealing experiment of supersaturated low-temperature substitutional gold in silicon was made by an ordinary annealing method. The gold concentration was determined from the resistivity by a four-point probe method, the Hall coefficient and DLTS with no appreciable difference in the results. The dependences of the annealing characteristics upon the temperature and the initial value of the gold concentration were examined. The annealing was represented by a firstorder reaction and the time constant decreased with an increase in the initial value. From these results, it was concluded that homogeneous nucleation occured during the annealing and that a strain energy of low-temperature substitutional gold decreased with nucleus formation.