Yusuke Mizokawa

Evaluation of the initial oxidation of heavily phosphorus doped silicon surfaces using angle-dependent X-ray photoelectron spectroscopy

Abstract The room temperature oxidation of heavily P-doped Si(100) and poly-Si prepared by HF-treatment has been monitored for a period of about 1 year, using angle-dependent X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM), Immediately after HF-treatment, the P/Si atomic ratio increased with decreasing the photoelectron take-off angle, which implies that the more segregated-P existed in near the top surface region. The amount of activated Si, whose binding energy of Si2p was lower by 0.5 eV referred to that of lattice Si related to the amount of segregated-P closely. In the case of the P-doped samples, the chemical composition of the growing oxide films showed that not the Si ++ but the Si 3+ state was the dominant component until the oxide thickness, d , went up to over ~1.5 nm, while the Si 4+ was the major species for the moderately doped Si(100) and nondoped poly-Si, except in the very initial oxide ( d ). In contrast to the smooth AFM image of the moderately doped Si(100) surface, the heavily P-doped Si(100) showed very unique geometrical pattern.

Concentration of point defects changed by thermal stress in growing CZ silicon crystal: effect of the growth rate

Behavior of point defects under thermal stress in growing Czochralski (CZ) silicon is theoretically examined. The changes in point defect concentration by the thermal stress depending on the growth rate are quantitatively estimated, and their contributions to the formation of secondary defects are discussed.

Concentration of point defects in growing CZ silicon crystal under the internal stresses: effects of impurity doping and thermal stress

Abstract Behavior of point defects under the internal stress in a growing Czochralski (CZ) silicon is theoretically examined. The changes of point defect concentration by the impurity doping and by the thermal stress are quantitatively estimated. Contributions of them to the formation of secondary defects are discussed.

Annealing behavior of phosphorus in native oxide films on heavily phosphorus doped silicon

Abstract Phosphorus redistribution and its chemical structure in the native oxide/Si as well as thermal oxides (∼ 30 nm)/Si were investigated using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The Si substrates were both heavily P-doped Si(100) and poly-Si, together with nondoped poly-Si. The in-depth profiles of P obtained by both XPS and SIMS showed that the dopant-P redistributed in the thin native oxide film (NOF) even at room temperature, and the amount of P increased drastically upon annealing. The amount of redistributed P was much larger for Si(100) than for poly-Si. The dominant chemical structure of P was not P2O5 but elemental-P and/or Si-P. Clear pileup of P at theNOF/Si interface could not be observed, since the thickness of NOF is very thin and probably P diffused into throughout the NOF. In the case of thermal oxides, both SIMS and XPS profiles exhibited a big pileup-P at the oxide/Si interface. The amount of pileup-P was about two times larger for the Si(100) than for the poly-Si, and it increased with annealing temperature. In the oxide films, the31P in SIMS as well as P0 and P2O5 features in XPS were also detected, although the intensities were very weak compared to those at the interface.

Phosphorus redistribution in the surface region of heavily phosphorus doped silicon

Abstract Heavily phosphorus doped samples of both Si(100) and polycrystalline silicon (poly-Si) together with nondoped poly-Si were examined using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The surfaces were treated by HF or a mixed solution of HCl, H 2 O 2 and H 2 O. The Si2p photoelectron spectra from the heavily P-doped samples showed a new peak at below 0.4 eV from the Si 0 state, which suggests that the Si-P bond and/or activated Si atoms with dangling bond exist in the surface region of as large as several nanometers. This is further supported by the analysis of P2p spectra. A lots of P atoms diffused to the surface and broke the Si-Si bond, which caused the surfaces chemically unstable. Consequently, although the H-terminated nondoped poly-Si surface showed no oxide features, the heavily P-doped samples of both Si(100) and poly-Si exhibited 0.5–1 nm thick oxides. The sputter profiles of XPS and SIMS revealed that P atoms redistributed in the thin native oxide film and formed not P 2 O 5 but Si-P and/or elemental-P, even without intentional heating. The P-segregation was much more pronounced for the single crystal Si than for the poly-Si.

Superconductivity in Bi-2212 thin films of Bi2Ln0.3Ca2.7Cu2Oz (Ln=Pr, Nd, Sm, Eu and Gd) prepared by laser ablation method

Abstract The Bi-2212 thin films of the Bi2Ln0.3Ca2.7Cu2Oz system (Ln=Pr, Nd, Sm, Eu and Gd) have been prepared by the laser ablation method. The films are of metastable Bi-2212 phase, which has not been synthesized by the solid state reaction method. The highest zero resistivity temperature (Tcz) of 57 K has been found for the film with Ln=Pr, and the valence of Pr determined by XPS measurement was trivalent. Further, each of the films with various Ln elements had a Tcz value higher by 12–45 K than the corresponding sample of the bulk Bi2Ln0.5Ca2.5Cu2Oz system.

Superconductivity in Bi-2212 thin films of Bi2LaxCa3−xCu2Oz prepared by laser ablation method

Abstract We have synthesized Bi-2212 thin films of Bi 2 La x Ca 3− x Cu 2 O z with the composition range of 0.2≤ x ≤0.7 by the laser ablation method. Bi-2212 samples with the same range of composition have not been obtained by solid state reaction except the sample with x =0.5. The film with x =0.2 showed the highest starting temperature of diamagnetic signal ( T cm ) at about 78 K, and it changed from superconductor to insulator with increasing La content x .

Equilibrium concentration of vacancies under the anisotropic stress field around and impurity

Equilibrium concentration of vacancies under the anisotropic stress field around an impurity is investigated. The anisotropy of the work by anisotropic stress is considered. Threshold change of equilibrium concentration of vacancies corresponding to the reported change of void density by B and Sb doping is found. By using this, we can predict the void density change in doped Si.

New Bi-cuprate thin films of Bi2(La,Ca)2Can−1CunOz (n=3, 4, 5, 6 and 7) prepared by the laser ablation method

Abstract We have synthesized new layered Bi-cuprate thin films of Bi2(La,Ca)2Can−1CunOz (n=3, 4, 5, 6 and 7) by the laser ablation method. These materials are metastable phases that have not been synthesized by standard solid state reaction method. The lattice parameter c was 36.6, 43.1, 49.4, 56.0 and 62.5 A for the n=3 (2223), n=4 (2234), n=5 (2245), n=6 (2256) and n=7 (2267) phases, respectively. All the films showed semiconductor-like temperature dependence with no trace of superconductivity down to 4.2 K.

Preparation of Bi-2201 thin films Bi2LnxCa2−xCu1Oz (0.4 ≦ x ≦ 0.8, Ln=La, Pr, Nd, Sm, Eu and Gd) by laser ablation

We have prepared Bi-2201 thin films of Bi2LnxCa2−xCu1Oz systems (Ln=La, Pr, Nd, Sm, Eu and Gd) by the laser ablation method. In the Bi2LaxCa2−xCu1Oz system, the Bi-2201 films have been obtained in a wide composition range of 0.4≦x≦0.8, and the films with x<0.7 have been of the metastable phase, which has never been reported to be synthesized by the solid state reaction method. The film with x=0.4 has shown the lowest resistivity in the Bi2LaxCa2−xCu1Oz system, and in the Bi2LnxCa2−xCu1Oz systems (Ln=La, Pr, Nd, Sm, Eu and Gd), when x is fixed to 0.4, the film with Ln=Nd has shown the lowest resistivity. From the results of resistivity and magnetic measurements, however, none of these films have been found to be superconductive.