Hiroyuki Fujimori

Micro-emulsion synthesis of monodisperse surface stabilized silicon nanocrystals

Silicon nanocrystals with a uniform size distribution were synthesized in inverse micelles using powerful hydride reducing agents. The silicon nanocrystals surfaces were then stabilized with 1-heptene to produce particles with strong blue photoluminescence.

Defect Propagation from 3C-SiC Intermediate Layers to III–Nitride Epilayers

The propagation of crystal defects from a 3C-SiC intermediate layer (3C-SiC IL) to hexagonal III–nitride epilayers formed by a metalorganic vapor phased epitaxy (MOVPE) has been investigated by observing the interface between the 3C-SiC IL and the hexagonal III–nitride epilayers. The 3C-SiC(111) IL grown on a Si(111) substrate has many stacking faults (SFs) that form along the 3C-SiC111 planes. The density of the SFs decreases with separation from the Si substrate. The initial III–nitride epilayers have V-shaped trenches due to the SFs of the 3C-SiC IL. However, there are some SFs, that do not generate V-shaped trenches. On the basis of high-resolution cross-sectional observations by transmission electron microscopy and X-ray pole-figure analysis, an atomic model for the SFs is considered in terms of twin bands of 3C-SiC. V-shaped trenches were determined to be formed on protrusions consisting of the twin bands in the 3C-SiC IL.

Depth Effect of the Morphology Change Induced by Hydrogen Annealing of Grown‐in Defects in Silicon

We study the depth dependence of the morphology of grown-in defects in as-grown in silicon and after hydrogen annealing. Recently, it has been reported through atomic force microscopy observation that the morphology of grown-in defects depends on the thermal annealing temperature. However, it is not possible to fully observe the detailed morphology of grown-in defects from the etched surface. In this paper, we discuss the dependence of the morphology of grown-in defects relative to their depth from the surface in silicon crystals after hydrogen annealing at 1200°C for 1 h transmission electron microscopy observation. Near the surface, the morphology of grown-in defects is a 122-sided polyhedral. With increasing depth, the morphology of grown-in defects approaches an octahedron. It is concluded that the morphology of grown-in defects becomes polyhedral because of oxygen out-diffusion and the movement of silicon atoms under high temperature annealing.

The Interrelation Between the Morphology of Oxide Precipitates and the Junction Leakage Current in Czochralski Silicon Crystals

We have studied the interrelationship between the morphology of oxide precipitates and the p-n junction leakage current in Czochralski silicon crystals. It is well known that the p-n junction leakage current can be used to measure the electric characteristic near the surface of a silicon wafer. After we measured the p-n junction leakage current, we studied the morphology of the oxide precipitates under the p-n junction by transmission electron microscopy. The junction leakage current characteristics are almost the same for both preannealing at 780°C for 24 h and 1000°C for 7 h and for preannealing at 1200°C for 0.5 h. In addition, the oxide precipitates near the surface were almost all in the form of polyhedrals in both preannealing types. However, in a dose of ten times for preannealing at 1200°C for 0.5 h, the morphology of oxide precipitates near the surface were polyhedrals with dislocation. That is to say, the morphology of oxide precipitates has been affected by a dose of ion implantation. In this paper, we discuss the effects of junction leakage current characteristics on the morphology of oxide precipitates in the near‐surface area.

Determination of silicon evaporation rate at 1200 °C in hydrogen

Separation by implanted oxygen silicon wafers have been investigated with cross‐sectional transmission electron microscopy after annealing at 1200 °C in argon as well as in hydrogen. It is observed that the buried oxide has experienced little change in the thickness, which is ascribed to the low hydrogen solubility in the crystal (about 3×1015 cm−3) and provides a natural mark to measure the thickness variation of the top silicon directly. The evaporation rate as determined in this method is less than 0.1 nm/min with an accuracy of ±0.1 nm/min, at least two orders of magnitude lower than reported in previous investigations.

The morphology of grown-in defects in nitrogen-doped silicon crystals

The grown-in defects in Czochralski silicon crystals have been well known as a void-type shape. Recently, it has been reported that in nitrogen-doped silicon crystals the grown-in defects are formed in some different shapes. The density of these defects in nitrogen-doped silicon crystals is remarkably higher than that of Czochralski silicon crystals. We study the morphology of grown-in defects and the morphological change of grown-in defects on annealing in nitrogen-doped silicon crystals with transmission electron microscopy. This showed that there is one kind of nitride precipitate in nitrogen-doped silicon crystals. The growth of whisker-like defects is identified in nitrogen-doped silicon crystals after hydrogen annealing. Nitrogen and oxygen are detected from these whisker-like defects. The whisker-like defects contain both a distorted diamond structure and an amorphous structure that was clarified by the high-resolution transmission electron microscopic images.

Characterization of Dislocations in GaN Thin Film and GaN/AlN Multilayer

The dislocations in GaN thin film with GaN/AlN multilayer (ML) as the buffer layer were evaluated using transmission electron microscopy. A high density of dislocations parallel to the GaN/ML interface and a sudden decrease in the dislocation density at the GaN/ML interface were found. Dislocation propagation in the direction parallel to the GaN/ML interface by turning horizontally on the GaN/ML interface is considered to be effective in decreasing the dislocation density at the top layer of GaN.

Defect Propagation from 3C-SiC to III-Nitride

Role of 3C-SiC intermediate layer (3C-SiC IL) and a propagation of crystal defects from 3C-SiC IL to III-nitride epilayers has been investigated by observing the interface between the 3C-SiC IL and III-nitride epilayers. We found that better quality epilayers were obtained by using such intermediate layers than by direct growth on Si substrates. In the case of III-nitride epilayers grown directly on Si, the layers grown at the initial stage are not flat. The 3C-SiC IL grown on Si (111) substrates has many stacking faults (SFs) that form along the 3C-SiC {111} planes. The initial III-nitride films have V-shaped trenches due to the SFs of the 3C-SiC IL. However, some SFs do not lead to the V-shaped defects.