A new and more `generalized' grazing-incidence-angle X-ray diffraction (G-GIXD) method which enables simultaneous measurements both of in- and out-of-plane diffraction images from surface and interface structures has been developed. While the method uses grazing-incidence-angle X-rays like synchrotron radiation as an incident beam in the same manner as in `traditional' GIXD, two-dimensional (area) detectors like image plates and a spherical-type goniometer are used as the data-collection system. In this way, diffraction images both in the Seemann–Bohlin (out-of-plane) and GIXD geometry (in-plane) can be measured simultaneously without scanning the detectors. The method can be applied not only to the analysis of the in-plane crystal structure of epitaxically grown thin films, but also to more general research topics like the structural analysis of polycrystalline mixed phases of thin surface and interface layers.
ABSTRACTThe photoluminescence (PL), its temperature dependence and X-ray diffraction (XRD) have been studied in MBE grown GaAs/AlGaAs/InGaAs/AlGaAs /GaAs quantum wells (QWs) with InAs quantum dots embedded in the center of InGaAs layer in the freshly prepared states and after the thermal treatments during 2 hours at 640 or 710 °C. The structures contained two buffer (Al0.3Ga0.7As/In0.15Ga0.85As) and two capping (In0.15Ga0.85As / Al0.3Ga0.7As) layers. The temperature dependences of PL peak positions have been analyzed in the temperature range 10-500K with the aim to investigate the QD composition and its variation at thermal annealing. The experimental parameters of the temperature variation of PL peak position in the InAs QDs have been compared with the known one for the bulk InAs crystals and the QD composition variation due to Ga/Al/In inter diffusion at thermal treatments has been detected. XRD have been studied with the aim to estimate the capping/buffer layer compositions in the different QW layers in freshly prepared state and after the thermal annealing. The obtained emission and XRD data and their dependences on the thermal treatment have been analyzed and discussed.
ABSTRACTAn In(Ga)As-based self-assembled quantum dot laser test structure grown on strain-relief Al0.5Ga0.5As1-ySby strain-relief buffer layers (0≤y ≤ 0.24) on a GaAs substrate is investigated in an effort to increase dot size and therefore extend the emission wavelength over conventional InAs quantum dots on GaAs platforms. Cross-section transmission electron microscopy, and high-resolution x-ray diffraction are used to monitor the dislocation filtering process and morphology in the buffer layers. Results show that the buffer layers act as an efficient dislocation filter by drastically reducing threading dislocations, thus providing a relaxed, low dislocation, compositionally modulated Al0.5Ga0.5Sb0.24As0.76 substrate for large (500Å height x 300Å width) defect -free InAs quantum dots. Photoluminescence shows a ground-state emission of the InAs quantum dots at 1.45 μm.
ABSTRACTIn this work, we report optical and structural properties of vertical aligned self-assembled InAs quantum dots multilayers. The InAs quantum dots samples were grown by Molecular Beam Epitaxy. Employing Atomic Force Microscopy, Transmission Electron Microscopy, and Gracing Incident X-ray Diffraction we have studied the structural properties of samples with different number of periods of the multiplayer structure, as well as different InAs coverage. The optical properties were studied using Photoluminescence spectroscopy.
Density dependent composition of InAs quantum dots extracted from grazing incidence x-ray diffraction measurements