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We have developed an instrument for real-time observation of silicon carbide (SiC) crystal during the sublimation growth process by x-ray topography. It is constructed by combining an x-ray goniometer and a crystal-growth chamber. The vertical goniometer consists of three circles, an α circle for the x-ray source, a β circle for the detector, and a φ circle for the azimuthal rotation of the sample. The growing crystal boule is set at the center of the goniometer glued on a crucible lid. Transmission topographs are taken using an asymmetric (1011) reflection with the scattering angle 2θB=β−α from the (0001)-oriented boule. A rotating-anode 18 kW generator with a molybdenum target is employed as the x-ray source. Topographs are observed by a direct imaging system using a charge-coupled device camera. Incident and scattered x-ray beams pass through beryllium windows mounted on the bottom and top flanges of the crystal-growth chamber, respectively. The crucibles are also designed for in situ measurements so ...

Oxide layers etched at an angle were fabricated on a 6H‐SiC substrate by varying etching time in diluted hydrofluoric acid, and 6H‐SiC metal–oxide–semiconductor structures with various oxide thicknesses were formed. High‐frequency capacitance–voltage measurements were carried out for determining the change in gate voltages corresponding to the midgap condition as a function of the thickness of the oxide layer, and the depth profile of trapped charge density in the oxide was estimated from the result. It is found that negative charges build up near the 6H‐SiC/SiO2 interface, and that positive charges accumulate in the region at 40 nm from the interface. No significant difference is observed in the depth profiles of the trapped charge density between the oxide layers on the carbon and silicon faces. The origin of these trapped charges is discussed in conjunction with the carbon‐related compounds in the oxide layers.

Photoluminescence (PL) has been used to study defects introduced by 1‐MeV‐electron irradiation in cubic silicon carbide (3C‐SiC) films epitaxially grown on Si substrates by means of chemical vapor deposition. A dominant PL line of 1.913 eV observed in 3C‐SiC irradiated with electrons was found to disappear at annealing stages of ≊100 and 700 °C. The annealing stages of the 1.913 eV PL center and its fraction annealed at each annealing stage were in good agreement with those obtained for the T1 electron spin resonance center, which is attributed to isolated vacancies at silicon sublattice sites [H. Itoh, M. Yoshikawa, I. Nashiyama, S. Misawa, H. Okumura, and S. Yoshida, IEEE Trans. Nucl. Sci. NS‐37, 1732 (1990)]. This result indicates that the 1.913 eV PL line arises from silicon vacancies in 3C‐SiC. The characteristics of other PL lines induced in 3C‐SiC epilayers by irradiation are also discussed.

Critical current densities Jc were measured in as‐deposited, c‐axis‐oriented Bi2Sr2Ca2Cu3Ox thin films with Tc values as high as 97 K, which were prepared by metalorganic chemical‐vapor deposition. These films showed high Jc (≳109 A/m2) at 77.3 K in high magnetic fields (≥1 T, H∥a‐b plane). The best values are 3.3×109 A/m2 at 1 T and 9.1×108 A/m2 at 8 T, which are the highest Jc for Bi‐oxide thin films among those reported so far. There were no signs of weak links in the Jc(H) behavior, and the surface morphology examined by scanning electron microscopy showed no apparent grain boundaries. The values of Jc decreased sharply when the applied field deviated from the a‐b plane, and went to zero at the angles where the field component in the c direction is nearly equal to the irreversibility field Hc2* parallel to the c axis. The angular dependence of Jc of these films is most reasonably explained by the theory of intrinsic pinning.

Radiation effects on cubic silicon carbide (3C‐SiC) metal‐oxide‐semiconductor (MOS) structures have been studied with high‐frequency capacitance‐voltage measurements. It was found that interface traps are generated at the 3C‐SiC/SiO2 interface and oxide‐trapped charges are built up in the oxide by 60Co gamma‐ray irradiation. The generation of the interface traps and the oxide‐trapped charges are affected by bias polarity applied to the gate electrode during the irradiation. Absorbed dose dependencies of their generation are discussed comparing with those of Si MOS structures.

The oxygen partial pressure dependence of the Silicon carbide (SiC) oxidation process was investigated using in-situ spectroscopic ellipsometry at oxygen partial pressures between 1 and 0.02 atm for 4 H-SiC (0001) Si- and (000−1) C-faces. Analyses of the interface structure between the oxide and SiC indicate that the interface layer has a modified SiC-like structure around 1 nm thick accompanied by oxide growth; the structure and thickness do not change after an oxide growth of about 7 nm. The oxide thickness dependence of the growth rate at sub-atmospheric oxygen pressures is similar to that at 1 atm pressure, that is, just after oxidation starts, the growth rate rapidly decreases as the oxidation proceeds. After an oxide growth of about 7 nm thick, the deceleration of the growth rate suddenly changes to a gentle slope. The thickness at which deceleration changes depends slightly on both the oxygen partial pressure and surface polarity of the SiC substrate. The origins of these two deceleration stages, i...

Wet and dry oxide films-4H-SiC epitaxial (000 (1) over bar) C-face interfaces have been characterized by capacitance-voltage (C-V) measurements and soft x-ray excited photoemission spectroscopy (SX-PES) and hard x-ray excited photoemission spectroscopy (HX-PES) using synchrotron radiation. The interface state density for wet oxidation is much smaller than that for dry oxidation at any energy level. In the PES measurements, intermediate oxidation states such as Si1+ and Si3+ were observed. In addition, the areal densities of these states were found to be in a good correspondence with those of the interface states. The reasons for the good electrical characteristics of metal-oxide-semiconductor devices fabricated by wet oxidation are discussed in terms of the depth profiles of oxide films derived from the SX-PES and HX-PES results. (c) 2006 American Institute of Physics., copyright(c)2006 American Institute of Physics.

Single‐crystal films of the solid solution AlxGa1−xN of the entire composition range have been fabricated on sapphire and silicon substrates by reactive molecular beam epitaxy (MBE) at 700 °C. The properties of the films have been studied by the reflection high energy electron diffraction technique, x‐ray diffraction, and electrical and optical measurements. The lattice constant of the film is not a linear function of the composition, and the fundamental absorption edge also shows nonlinear dependence on the composition. The narrow intense peak of the cathodoluminescence concerned with the band to band or shallow impurity band transition, varies from 3.4 to 6 eV with the composition, which suggests the feasibility of AlxGa1−xN films grown by reactive MBE for optical devices in the ultraviolet spectral region.

Electrical properties of unintentionally doped n‐type and Al‐doped p‐type 3C‐SiC layers, epitaxially grown on Si by chemical vapor deposition, have been investigated at temperatures between 10 and 1000 K. Activation energies of Al acceptors and residual donors obtained from the temperature dependence of carrier density are 160 and 18 meV, respectively. 40%–60% of Al acceptors in the p‐type epilayers are compensated, and hole mobility is limited by acoustic phonon scattering above 300 K and by ionized impurity scattering below 250 K.

Ion backscattering in conjunction with channeling and blocking has been used to study the Ni‐SiC(001) system after Ni deposition at room temperature and after annealing up to a temperature of 870 K. Detailed analysis of the energy spectra of backscattered ions reveals morphology and composition on an atomic scale. The results show that up to the Ni coverage studied (14.1×1015 Ni atoms/cm2) no mixing occurs between Ni and Si or Ni and C at room temperature. At a temperature of 570 K, Ni starts to react with Si and forms a disordered film with a composition close to that of Ni2Si. Prolonged annealing at temperatures up to 870 K does not result in reaction to Si‐richer silicide phases. Upon annealing, C segregates to the surface of the Ni2Si film to form a layer of graphite.

Internal stress in 3C‐silicon carbide (SiC) epilayers grown on Si substrates by chemical vapor deposition was studied using Raman scattering. The stress in the epilayers grown on Si(001) at 1350 °C was found to be 5.4×109 dyn/cm2 tensile, which is comparable to that of silicon on sapphire. The magnitude of the stress is discussed in terms of the elastic deformation theory. It was found that there is not so much difference between the stress in 3C‐SiC epilayers grown on Si(001) and that in 3C‐SiC on Si(111) as the elastic deformation theory suggests.

Carbon films were deposited using mass‐separated C+ ions of 300 and 600 eV. The films have diamond‐like characteristics such as transparency in the visible spectral region with wavelengths longer than about 650 nm and in the infrared, and high electrical resistivity. Transmission electron diffraction analysis shows that the film is amorphous and does not contain graphitically bonded carbon atoms. Kα x‐ray emission spectrum of the carbon in the film agrees well with that of diamond. In the x‐ray photoemission spectrum of the film, no characteristic energy loss due to π plasmon was observed. The atomic density of the film calculated from the energy loss due to the plasma oscillation of valence electrons is 1.7×1023 atoms/cm3, which is in good agreement with that of diamond. These results indicate that the film deposited using C+ ion beam consists of tetrahedraly bonded carbon atoms.

Aluminum doping was performed using triethylaluminum as the dopant in chemical vapor deposition of 6H–silicon carbide (SiC). Measurements on the electrical and cathodoluminescent properties of the epilayers indicate that the doping concentration of aluminum can be easily controlled by the flow rate of metalorganics. Electroluminescence was also observed for the pn junctions prepared by the successive growth of a nondoped n layer and a p layer doped with aluminum using metalorganics.

Heteroepitaxial growth of SiC polytypes, 3C‐ and 6H‐SiC, has been studied by chemical vapor deposition. Raman spectra were used to identify the polytypes. 3C‐SiC and 6H‐SiC were grown on 6H‐SiC at low (1330–1500 °C) and high temperatures (1700–1800 °C), respectively. On the other hand, on 3C‐SiC, only 3C‐SiC was grown at all the temperatures. 3C‐SiC epilayers grown at high temperatures have smooth surfaces and good electrical properties compared with those grown at low temperatures.

Heteroepitaxial growth of 3C‐ and 6H‐silicon carbide (SiC) was investigated using Raman scattering. It was found that 3C‐SiC(111) can be epitaxially grown on 6H‐SiC(0001) by chemical vapor deposition, and that Raman spectra are useful for identification of heterostructure of thin layers.