Sumitomo Electric Industries, Ltd. (Osaka, Japan) has developed 6-inch diameter GaN (gallium nitride) substrates to be used for white LEDs. The front face of the GaN substrates is a polarized c-plane. Polarity refers to a change in the electrical characteristics of a crystal caused by the preferred orientation of the constituent elements, and c-plane is a crystal face of a GaN substrate generally used for white LEDs and blue-violet or blue lasers. With positively-charged Ga and negatively-charged N oriented alternately, c-plane exhibits a strong polarization. This polarization decreases light-emitting efficiency in the green region. The GaN substrates have excellent thermal conductivity.