利用拉曼光譜研究硒化錳鋅在高壓下之相變化

Abstract

本文是利用拉曼光譜研究硒化錳鋅在高壓下之相變化。利用鑽石高壓砧的技術產生高壓，使得硒化鋅摻入低濃度錳元素的晶體結構由四配位的閃鋅礦(ZB)結構轉變成六配位的氯化鈉(RS)結構。 在拉曼光譜圖中，當壓力分別增加至13.5Gpa(Mn=2.6%)和12.8GPa(Mn=7.0%)時，LO和Mn impurity模完全消失，即產生半導體─金屬結構變化。在金屬相變前，TO模產生兩次的分裂，其壓力分別為4.5GPa和6.3GPa(Mi=2.6%)，以及6.2GPa和7.1GPa(Mn=7.0%)。除了TO分裂模split Ⅰ隨壓力增加呈現紅位移之外，LO，TO，TO分裂模splitII以及Mn impuroty模皆呈藍位移的趨勢。

In this work, the mixed crystals, diluted magnetic semiconductors Zn0.974Mn0.026Se and Zn0.93Mn0.07Se, were studied by Raman scattering spectroscopy up to 32.4 GPa and 12.8 GPa, respectively. The high pressure was generated by using the gasketed diamond anvil cell (DAC). The semiconductor-metal phase transition pressures for these crystals occurred at 13.5 GPa and 12.8 GPa, respectively. The metallization occurred when the crystal structure transformed from a four-coordinated zinc-blende (ZB) phase into a six-coordinated rock salt (RS) phase. Before the semiconductor-metal phase transition, two new phase transitions exhibiting TO Raman mode splitting were observed at 4.5 GPa (split mode Ⅰ) and 6.3 GPa (split mode Ⅱ) for Zn0.974Mn0.026Se and at 6.2 GPa and 7.1 GPa for Zn0.93Mn0.07Se, respectively. The pressure effects on the phonon modes of LO, TO and TO split mode Ⅰ exhibited similar blue shift behavior as the Mn local phonon mode. On the contrary, the TO split mode Ⅱ exhibited red shift. The LO and Mn local mode disappeared as the pressure was higher beyond the metallization pressure, where the TO split phonon modes were still able te be observed.