[17a-Z27-1~9] 15.4 III-V-group nitride crystals

[17a-Z27-5] Origin of black color in OVPE-GaN (heavily O-doped GaN) crystals

〇Tomoaki Sumi¹, Junichi Takino¹, Yoshio Okayama¹, Akira Kitamoto², Shigeyoshi Usami², Masayuki Imanishi², Yusuke Mori² (1.Panasonic Corp., 2.Osaka Univ.)

Keywords:gallium nitride, vapor phase epitaxy, crystal color

In semiconductor materials, doping technique is mainly introduced for controlling the electrical properties. Some research groups reported growth of low-resistivity n-type gallium-nitride (GaN) crystals by doping oxygen or silicon because low resistivity n-type substrate is demanded for reducing power loss of GaN power devices. They reported that crystal color turned black with increasing n-type additive concentration though oxygen and silicon atoms behave as shallow donors in GaN. Here, we explain why heavily doped n-type GaN crystals exhibit low transparency. From optical absorption profiles and a theory of band tails, we concluded that Ga vacancy and a Ga vacancy complex with oxygen merge the band tail because of the large number of the charges, which increases absorption coefficient in the visible spectra range.