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 crucible. The surface of the grown wafer was fully composed of the c-plane and showed low oxygen concentration, so expansion of lattice constants could be successfully prevented.

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 μm away disappeared by annihilating each other as growth proceeded, and this is one of the mechanisms underlying the dislocation density reduction. The moving distance of dislocations before annihilation is uncommon and a unique phenomenon in the Na-flux method.

No abstract

This paper discusses Nianchan a diary published in 1958. This diary was written by Sueko Yasmoto who is Zainicih Korean and who lives in a coal mine at the age of the ten. The results of this paper indicate that this diary represents her unstable identity based on a boundary between adult and child, and Zainicih Korean and Japanese. She writes in her diary about the discrimination against Zainicih Korean coal miners by the Japanese; not only the tone of writing makes such a claim, but also the fact that it is written in Roman characters, not Japanese. I examined the position of the author as a Zainicih Korean coal miner by researching the context, including the increase in the number of unemployed Zainicih people at coal mines during the 1950s. And, as a child of Zainicih Korean who was educated in Japanese language through 'Seikatsu Tsuzurikata kyōiku', after the war. Also, I analyzed that a description in the Roman alphabet represents the relationship of the author with three readers: her teacher, older brother, and her friend. Ultimately, I argue that a description in the Roman alphabet is a result of self-censorship to leave a trace of discrimination, but not to convey directly to the three readers. It is significant which unstable identity she chooses between adult and child, and Zainicih Korean and Japanese.