Growth and Characterization of Diluted Magnetic Semiconductors GaMnN Thin Films and Nanorods

• Main Authors: Yuan-Ting Lin, 林員梃
• Other Authors: Li-Wei Tu
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/72wf5v

博士 === 國立中山大學 === 物理學系研究所 === 102 === Plasma-assisted molecular beam epitaxy growth and characteristics of GaMnN diluted magnetic semiconductors, including epitaxial thin films and one-dimensional nanorods, are investigated in this dissertation. Both homogeneously doped and delta-doped techniques are adopted to grow GaMnN thin films. Mn homogeneously doped high crystal quality GaN thin films were grown on c-sapphire with low-temperature GaN buffer layer. Mn atoms successfully substitute the Ga sites in wurtzite structure. GaMnN thin film exhibits 5.5% negative magnetoresistance (MR) at 10 K. The MR drastically drops above 50 K. The temperature dependence magnetization measured by superconducting quantum interference device (SQUID) is about 50 K Curie temperature of GaMnN. Furthermore, the crystallinity of delta-doped GaMnN thin film is verified by high-resolution x-ray diffraction (HRXRD) and transmission electron microscopy (TEM). The zero-field-cool (ZFC) and field-cool (FC) curves and anomalous Hall Effect (AHE) indicate the Curie temperature of the thin film sample is 190-200 K. The GaMnN nanorods are also grown by PAMBE with homogeneously and delta-doping techniques. The Raman scattering and SQUID measurements indicate the interstitial or nano-sized clusters of Mn may form in homogeneously doped nanorods. Excessive Mn atoms form an amorphous layer between nanorods and substrate. The growth period of delta-doped nanorods is studied for minimizing the formation of Mn related secondary phases and thereby enhancing the crystal quality of the nanorods. Above room temperature ferromagnetism of GaMnN nanorods is observed in the delta-doped nanorods. The anisotropic magnetism of nanorods shows that preferred direction for the magnetic moment alignment is not along the c-axis of GaMnN. The saturated magnetization of delta-doped GaMnN with 1.8% Mn content, obtained by increasing Mn flux during growth, is enhanced almost four times larger than homogeneously doped sample.