| Summary: | 碩士 === 國立交通大學 === 電子研究所 === 107 === The GaMnAs diluted magnetic semiconductor (DMS) has attracted much attention in the past two decades because of its physical models and potential applications in spintronics. In order to increase the Curie temperature of GaMnAs, it is necessary to increase the Mn content in GaMnAs. However, as increasing the Mn content will easily damage the lattice structure with ion implantation. In this study, we used helium ion beam induced epitaxial crystallization (He-IBIEC) as an annealing method. The penetrating helium ions will heat the damage region and regrow the thin film in a very short time to prevent Mn atoms from gathering and precipitating into secondary-phase clusters. After annealing the GaMnAs thin film under different energy of helium ions, we analyzed the bandgap energy of the GaMnAs thin film in relation to the crystalline quality and strain.
In order to increase the spin signal in GaMnAs, we provided excess carriers into the substrate by Mg ions implantation. The effective concentrations of Mg were 0.5%, 1%, 2% and 4%, respectively. Then, we implanted 2.6% Mn ions into GaAs: Mg samples. Subsequent use of the heavy ion accelerator and the Van de Graaff accelerator to repair the samples by He-IBIEC annealing method under 350 keV and 1 MeV, respectively.
The experimental results show that the helium ion annealing has a significant effect on the lattice constant through the (004) ω-2θ measurement of the high-resolution X-ray diffraction, and the full width at half maximum (FWHM) of the GaMnAs signal is reduced, that indicate the improvement of the crystal quality. In the RSM result which indicates that samples remained fully strained and the stress does not release. Then, the Raman measurement is used to observe the strain of the sample, because the peak shift of longitudinal optical mode is relate to strain. The peak shift is found to decrease with increasing the energy of helium ions. Based on the Raman signal intensity ratio of longitudinal optical and transverse optical mode of GaAs, the crystal quality of the sample is improved after annealing. The transmittance and reflectance were measured by a spectrophotometer. The bandgap energy of the GaMnAs thin film was extracted using Tauc plot method, and it is found that IBIEC annealing treatment increased the bandgap energy of GaMnAs. The increment of Mg ions concentration make the lattice constant larger but still remained fully strained. When the Mg ions concentration is increased, the overall crystal quality is deteriorated. And it needs annealed with 1 MeV to have enough energy to repair the crystal structure.
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