Masayoshi Adachi

Analysis of the Dislocation and Polarity in an AlN Layer Grown Using Ga?Al Flux

We have developed a novel liquid-phase epitaxial (LPE) technique that uses Ga–Al flux to grow AlN layers on nitrided sapphire substrates. In this study, cross-sectional and plan-view images were taken using a transmission electron microscope. An edge dislocation was dominant in the LPE AlN layers; its density was approximately 5×109 cm-2. Convergent-beam electron diffraction analysis revealed that the LPE layer had Al polarity, even though the nitrided sapphire layer had N polarity. The oxygen potential in the injecting N2 gas played an important role in the polarity inversion in the LPE growth.

The influence of temporal phase difference of m=±2 oscillations on surface frequency analysis for levitated droplets

The oscillations of an electromagnetically levitated molten silicon droplet were analyzed. Analysis was carried out under a superimposed static magnetic field, where the m=±2 oscillation is dominant and the droplet rotates. A phase unwrapping method was used to reveal sample rotation. The oscillation frequency of the longest diameter Dmax and difference of radii along the X and Y axes, R−, were analyzed using an image of the droplet as seen from the top of the sample. The m=+2 and m=−2 oscillations were analyzed theoretically using spherical harmonics, and it was found that a temporal phase difference between m=+2 and −2 oscillations causes apparent rotation of the samples, which causes unequal intensities of the m=±2 peaks which are split by the droplet rotation.

Does supercooled liquid Si have a density maximum

We have performed precise measurements of the density of supercooled liquid silicon (l-Si) in the temperature range of 1530-1800 K using an electromagnetic levitation (EML) technique with static magnetic fields. We also performed first-principles molecular dynamics simulation (FPMD) of supercooled l-Si. The observed density of the supercooled l-Si and the FPMD results show good agreement in the temperature range of 1530-1800 K. The structure of the supercooled l-Si also showed good agreement between the experimental measurements and FPMD simulations. Based on these results, we discuss nucleation in supercooled l-Si and also the existence of a density maximum in the supercooled l-Si, which is well known in water at 4 degrees C.

High-Quality AlN Layer Homoepitaxially Grown on Nitrided a-Plane Sapphire Using a Ga–Al Flux

We previously grew AlN layers with in-plane rotational domains on nitrided c-plane sapphire substrates using a Ga–Al flux method. In this study, we successfully grew rotational-domain-free AlN layers using nitrided a-plane sapphire substrates. The full width at half maximum values of the X-ray rocking curves of (0002) and (102) of the AlN layer were 90 and 392 arcsec, respectively. From the results of transmission electron microscopy, edge-type dislocations were observed to be dominant in the layer. Convergent-beam electron diffraction revealed the occurrence of polarity inversion at the interface between the AlN layer and the nitrided sapphire.

Real-time x-ray observation of solidification from undercooled Si melt

Grain refined microstructure is often obtained spontaneously in the solidification of metals and semiconductors from the undercooled melt without any external forces. Although it has been reported that the grain refinement is mainly caused by the fragmentation of the dendrites, the dynamic process of the fragmentation of dendrites has not been fully understood because only the microstructure after the solidification has been analyzed. Here, we present a time-resolved two-dimensional x-ray diffraction experiment on the solidification of Si from the undercooled melt. The number of diffraction spots observed at low undercoolings (ΔT<100K) did not increase at the plateau stage, while the diffraction pattern at medium undercoolings (100K<ΔT<200K) changed from the spots with the tail to rings with the lapse of time. Both this result and high speed video imaging suggested that the high-order arms of the dendrites mostly detached from the main stems because nucleation could not be expected at the melting point af...

Densities of Fe–Ni melts and thermodynamic correlations

The densities of liquid Fe–Ni alloys were measured accurately by combination of an electromagnetic levitation technique and a static magnetic field. The static magnetic field suppressed the surface oscillation of the levitated sample droplet, which reduced the experimental uncertainty in the density measurement. Densities were determined over a wide temperature range and included a supercooled region. The densities of all Fe–Ni alloys investigated vary linearly with temperature over the range of measurements. The excess volumes were slightly positive over the entire composition range. The results were discussed within a thermodynamic framework using relationship between excess volume and thermodynamic properties such as excess Gibbs energy and enthalpy of mixing. The excess volume is correlated positively with excess Gibbs energy and enthalpy of mixing for various binary alloy systems.

Liquid Phase Epitaxy of Si-Doped AIN at 1300 °C in Ga-Al Melt

In the present study, we have successfully grown Si-doped AlN developed by solution growth technique using Ga-Al melt as a solvent under nitrogen atmosphere at 1300 °C. Si doping was introduced to the Ga-Al melt by adding pure Si metal. To allow homoepitaxial growth during solution growth experiment, sapphire substrate were nitrided with precise control to produce hiqh quality single crystalline AlN films with low dislocation density. With the help of AlN film template from above methods, we have successfully grown Si-doped AlN single crystalline layer with a flat surface and almost free from cracks. The full width at half maximum (FWHM) of x-ray rocking curve values for (0002) and (10-12) diffraction from the Si-doped AlN film were 43,2 and 594 arcsec, respectively.