Structural investigation of nanostructures by Extend X-ray Absorption Fine Structure (EXAFS) and Diffraction Anomalous Fine structure (DAFS)

点击翻译按钮获取中文摘要

InGaN/GaN semiconductors nanostructure are attractive due to their applications as blue laser diodes (DVD, HD printing), UV-light emitters (detection of bioterrorism, water purification), for white light generation (energy saving illumination) and electronic devices (in base stations, defense and space sattelites). InGaN/GaN quantum dots are together with CdSe/ZnSe dots promising materials for laser diodes in the green spectral region. The chemical compositions and ordering of atoms in crystal lattices of semiconductor nanostructures (quantum wells, wires and dots) are important parameters influencing substantially their electrical and optical performance. Therefore it is important to find a method that provides a comprehensive knowledge of the chemical compositions and of the local structure of such semiconductor nanostructures. The project deals with methods such as X-ray Absorption Near Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS) and Diffraction Anomalous Fine Structure (DAFS). Due to their atomic selectivity it can determine in quantum dots: the atomic ordering thus the chemical compositions and its gradient; the chemical shift of the absorption edge that is bond length and strain. The proposed methods are non-destructive in contrast to the Transmission Electron Microscopy (TEM). They probe also objects buried below the sample surface what it is essential for investigation of overgrown nanostructures and impossible to gain using Scanning Tunneling Microscopy (STM). Due to the access to the synchrotron radiation (SR) and its excellent properties such as high brightness, wide energy spectrum (synchrotron radiation is emitted with a wide range of energies, allowing a beam of any energy to be produced) it is possible to achieve information about nanostructures that cannot be obtained using standard methods (TEM, STM, X-ray Diffraction).