氧化鋅稀磁性半導體之X光吸收能譜研究

Abstract

由於自旋電子學的應用及其重要性，使的稀磁性半導體材料近年來蓬勃發展。其中，氧化鋅(ZnO)被預測有高於室溫的居禮溫度，並且其能隙大小約為3.3eV是Ⅱ-Ⅵ半導體材料中少數擁有直接能隙的材料之一。因此，關於氧化鋅的相關研究也被熱烈討論。然而，在氧化鋅中摻雜過渡金屬之後所產生的鐵磁性現象，其來源為何至今仍然沒有明確的理論或模型可以解釋。但許多實驗結果指出磁性氧化物半導體的鐵磁性質與樣品的製程條件息息相關。 X光能譜是用來了解樣品的電子結構非常有力的工具之一。由氧的吸收光譜可看出隨著樣品製程氧壓力的改變而有所不同，並且了解在鈷摻雜到氧化鋅樣品後能帶結構所產生的改變。而鈷的吸收光譜將可幫助我們判斷摻雜的鈷離子之電子組態。而我們同時將利用磁圓偏振二向性(XMCD)光譜與超導量子干涉儀SQUID來探討樣品的相關磁性。

Diluted magnetic semiconductors have attracted much attention due to their possible applications in spintronic devices, using both spin and charge degrees of freedom. In particular zinc oxide (ZnO), which has been predicted to have a Curie temperature above room temperature, has been studied with a wide range of transition metal dopants. However the ferromagnetic mechanism is still under debate. Many experimental results indicate that ferromagnetism in DMS is very sensitive to the preparation method and preparation conditions.

X-ray absorption spectroscopy is a powerful tool to investigate the electronic structures of 3d transition metal oxides. O K-edge XAS shows some changes in the spectral line shape which are attributed to defects such as oxygen vacancies. In additional, the XAS at Co L-edge show that Co ions are present in the Co2+(d7) state under tetrahedral symmetry. Magnetic properties were investigated with a superconducting quantum interference device (SQUID) and X-ray magnetic circular dichroism.