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Study of Mn-doped Ⅳ Group Diluted Magnetic Semiconductors by X-ray Absorption Fine Structure

Author: YeJian
Tutor: WeiShiQiang
School: University of Science and Technology of China
Course: Synchrotron Radiation and Applications
Keywords: X-ray absorption fine structure Si1-xMnx Ge1-xMnx Diluted magnetic semiconductors Magnetron sputtering XRD SQUID
CLC: O434.13
Type: PhD thesis
Year: 2009
Downloads: 302
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Abstract

The experimental method of this thesis, the use of synchrotron radiation X-ray absorption fine structure spectroscopy (XAFS) technology, combined with X-ray diffraction (XRD), atomic force microscopy (AFM) and Raman spectroscopy study jointly prepared by magnetron sputtering co-sputtering method Mn-doped diluted magnetic semiconductor film structure and performance of the group IV, the Mn ion valence, distribution and coordination environment of Mn-doped Si substrate and Ge-based samples structure parameters and magnetic properties. While taking advantage from exactly the real space Green function method FEFF8, theory based on an effective single-particle relativistic calculations, IV diluted magnetic semiconductor system Mn atoms of Mn-doped typical placeholder build models, analysis of the Mn atoms in the system presence of form and the placeholder situation, clear the Mn-doped Si dilute magnetic semiconductor thin films of Mn mainly exist substitutional Mn form of presence of Mn-doped Ge diluted magnetic semiconductors by doping amount decision. Using a superconducting quantum interference device (SQUID) measurement of Mn-doped Si dilute magnetic semiconductor thin film magnetic properties, results showed that the samples in the 50K temperature paramagnetic Mn atoms are combined to obtain the local structure information discussed from the microscopic structure sample structure and magnetic properties of the relationship, and thus controllable preparation for high-performance group IV diluted magnetic semiconductor structure and theoretical research base. In order to grow the dilute magnetic semiconductor film, as a main member to build an ultra-high vacuum magnetron sputtering apparatus, the main sputtering chamber (degree of vacuum of 6.6 × 10-6Pa) are equipped with four permanent target, into the sample chamber (vacuum degree 6.6 × 10-5Pa) equipped with a magnetic sample transfer means, the the sputtering growth rate was 0.3 to 3.0 nm / min controllable, Fe, Co, Ni, etc. can be realized a variety of magnetic metal material, metal material of Cu, Mn, Cr, etc. and semiconductor material such as Ge, Si, InSb, GaSb multi-target co-sputtering, the slew rate of the sample substrate from 0 to 30 rev / min, the sample was heated temperature of 0 ~ 1000 ℃ continuously adjustable. The use of the device, the quality of the Mn-doped group IV semiconductor thin film prepared by changing process parameters such as substrate temperature, sputtering pressure, the sample speed and annealing temperature. 1. Mn-doped Si-based diluted magnetic semiconductor thin film structure and magnetic studies using XRD, XAFS, and SQUID method to study the structure and magnetic properties of diluted magnetic semiconductor thin films of Si1-xMnx. XRD results indicate that the sample does not exist in the phase of the metal Mn clusters or the Si-Mn compound. Mn K edge XAFS results show that For all Mn doping content (3.0%, 5.0%, 8.0%) samples, Mn atoms are dispersed Si media. EXAFS fitting results show that Mn atoms and Si atoms, the nearest neighbor average coordination bond length of 2.35?, The coordination number of about 4.0, and Mn occupy alternative bit structure parameters are similar. To utilize FEFF8 program to simulate Mn occupy the Si lattice substitution bits, the four corners of the gap-bit and hexagonal interstitial sites of the three most representative theoretical models of the radial structure function curve, by comparison with the experimental curve, clear Mn samples mainly the form of alternate bits exist. The results of XRD and XAFS comprehensive that the Si1-xMnx prepared dilute magnetic semiconductor thin film samples does not have long-range order structure. In addition, XAFS fitting results show that the structure of the Mn-Si neighbor ligand disorder degree σ2Mn-Si (0.008 ~ 0.010? 2), indicating that much larger than the corresponding degree of disorder of the crystal Si sample structures exist certain distortions. The SQUID test results show that the samples were presented in the 50K temperature paramagnetic characteristics. First-principles electronic structure calculations show a deep level doping substitutional Mn 3d orbitals of the Mn atoms in Si-based system in the middle of the band gap can not with the Si 3sp track full hybrid, basically can not occur in dilute magnetic semiconductor described by the theory in the field of RKKY, double exchange ferromagnetic superexchange magnetic exchange interaction, leading to samples showed macroscopic paramagnetic. 2. Mn-doped Ge-based diluted magnetic semiconductor thin film structure XAFS, XRD, AFM and Raman spectroscopy methods to study the morphology and structure characteristics of a the Ge1-xMnx dilute magnetic semiconductor film. AFM results show a significant increase with increasing the doping amount of Mn, Ge1-xMnx dilute magnetic semiconductor surface roughness of the film sample. XRD results indicate that the Mn content is low (7.0%) in the sample, only observe the XRD diffraction peak corresponding to a polycrystalline Ge, the higher Mn content (25.0%, 36.0%) of the samples the apparent phase a diffraction peak, and Ge3Mn5 proportion with the increase of the Mn content increases. XAFS results indicate that the Mn content is low (7.0%) in the sample, Mn exists mainly in the form of alternate bits accounted for about 75%; higher Mn content (25.0%, 36.0%) of the sample, in addition to a small portion outside the alternate position of the Mn atoms, most of the Mn atoms in the form of Ge3Mn5 compound exists. Combination of Raman spectroscopy and GE K edge EXAFS spectra found that deteriorates With increasing the content of the Mn-doped Ge crystalline order, and from the lattice of the Raman spectrum can be found in the samples of the high content of Mn Ge There are obvious expansion.

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