The University of Osaka · Physics and Astronomy
Professor Masayuki Imanishi's research lab specializes in the development of high-quality bulk gallium nitride (GaN) single crystals using the Na-flux method, with a focus on enabling large-diameter, low-dislocation-density substrates essential for next-generation power and optoelectronic devices. The lab pioneers innovative techniques such as flux-film coating, coalescence growth from point seeds, and lateral overgrowth control to suppress defects and lattice distortion. Their work also extends to the fabrication and characterization of high-performance vertical GaN transistors, demonstrating excellent device performance with high breakdown voltage and low leakage current. The lab’s research bridges fundamental crystal growth science with practical applications in wide-bandgap semiconductor technology.
Figures are computed from collected data and may differ slightly.
Homoepitaxial hydride vapor phase epitaxy (HVPE) growth on GaN substrates grown with a Na-flux method, which is the most promising approach for fabrication of large-diameter, low-dislocation-density, fast-growing GaN wafers, was attempted for the first time. We found that, when different growth methods are combined, the differences in oxygen concentrations between a seed and grown crystal must be eliminated to maintain the crystallographic quality of the seed. Two kinds of Na-flux-grown seed cry
In a previous study, we successfully obtained large-diameter, low-dislocation-density GaN wafer using the Na-flux multi-point seed (MPS) technique. However, the lattice constants of the GaN wafer grown by this technique expanded due to oxygen concentration in pyramidal facets. We here invented a breakthrough technique for the promotion of lateral growth, and succeed in suppressing pyramidal facet growth by residual flux formed after extraction of the MPS-GaN substrate from the Na-Ga melt in a cr
We have recently shown that dislocation-free GaN crystals could be grown on a GaN point seed by the Na-flux method. To enlarge the diameter of dislocation-free GaN crystals, we propose here the coalescence of GaN crystals grown from many isolated point seeds. In this study, we found that two GaN crystals grown from two point seeds arranged along the a-direction coalesced without generating dislocations at the coalescence boundary, and the c-axis misorientation between two crystals around the coa
Abstract We recently invented a method called the flux-film-coated technique for purifying a GaN wafer with low dislocation density grown from point-seed crystals. In this study, we investigated the mechanism behind the reduction of dislocation density in the GaN wafer by evaluating the three-dimensional behavior of dislocations using multiphoton-excitation photoluminescence images. We made the surprising discovery that dislocations more than 50 μ m away disappeared by annihilating each other as
Abstract We have recently shown that dislocation‐free GaN crystals could be grown on a “GaN point seed” by the Na‐flux method. In order to grow larger‐diameter dislocation‐free GaN crystals, we have been trying to coalesce GaN crystals grown from many isolated point seeds. In this study, we found that two GaN crystals grown from two point seeds arranged along the a ‐direction coalesced without generating dislocations at the coalescence boundary. X‐ray rocking curve measurements showed that tilti
The Na‐flux method is expected to be a key GaN growth technique for obtaining ideal bulk GaN crystals. Herein, the structural quality of the latest GaN crystals grown using the Na‐flux method and, for the first time, the characteristics of a vertical transistor fabricated on a GaN substrate grown using this method are discussed. Vertical transistors exhibit normally off operation with a gate voltage threshold exceeding 2 V and a maximum drain current of 3.3 A during the on‐state operation. Addit
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