ゲルマニウム薄膜に誘起されたフリーキャリアによるフォノンのソフト化およびバンドギャップ変調に関する研究

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 鳥海 明, 東京大学教授 渡邉 聡, 東京大学教授 近藤 高志, 東京大学准教授 喜多 浩之, 静岡大学教授 田部 道晴University of Tokyo(東京大学

Experimental evidence of zone-center optical phonon softening by accumulating holes in thin Ge

We discuss the impact of free carriers on the zone-center optical phonon frequency in germanium (Ge). By taking advantage of the Ge-on-insulator structure, we measured the Raman spectroscopy by applying back-gate bias. Phonon softening by accumulating holes in Ge film was clearly observed. This fact strongly suggests that the phonon softening in heavily-doped Ge is mainly attributed to the free carrier effect rather than the dopant atom counterpart. Furthermore, we propose that the free carrier effect on phonon softening is simply understandable from the viewpoint of covalent bonding modification by free carriers