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[en] GaN films were fabricated by metal organic vapor phase epitaxy (MOVPE) on patterned sapphire substrates (PSSs) with either direct or inverse type patterned structures. Both of these two types of PSSs had their own unique GaN growth process which depart from the standard growth on the planar c-plane. GaN films on PSSs showed decreased threading dislocation (TD) density. However, differences between the crystal quality of the GaN films grown on PSSs were observed. It was also found out with one of the pattern type that the TD density varied laterally and followed the periodicity of the pattern on the sapphire surface.
[en] Large-area back-reflection and transmission X-ray diffraction topographs of bonded silicon-on-insulator (SOI) wafers made with synchrotron radiation allowed direct and simultaneous imaging of bonding-induced strain patterns of both the 7 μm thick (011) top layers and the (001) Si substrates of the SOI structures. The bonding-induced strain pattern consists of cells having a diameter of about 40 μm. Section topographs show a lattice misorientation of the adjacent cells of about 0.001° and the maximum observed strain-induced lattice plane rotation ten times larger, i.e. about 0.01°. Topographs made after etching away the insulator layer show no indication of residual strain or defects either in the silicon-on-insulator layer or in the substrate. This is in agreement with the experimentally determined maximum bonding stress of 30 MPa, which is much smaller than the estimated stress needed to nucleate dislocations. - Highlights: • SOI wafer strain consists of sharp-edged strain cells. • Bonding-induced strain patterns are not permanent in SOI wafers. • Observed stress was much lower than required for dislocation nucleation.
[en] This document gathers the transparencies that were presented at the international workshop on radiation imaging detectors. 9 sessions were organized: 1) materials for detectors and detector structure, 2) front end electronics, 3) interconnected technologies, 4) space, fusion applications, 5) the physics of detection, 6) industrial applications, 7) synchrotron radiation, 8) X-ray sources, and 9) medical and other applications
[en] Epitaxial GaAs material shows a great potential in X-ray spectroscopy and radiography applications due to its high absorption efficiency and low defect density. Fabrication of pixel radiation detectors from high-purtity epitaxial GaAs has been developed further. The process is based on mesa etching for pixellisation and sputtering for metallization. The leakage currents of processed pad detectors are below 10 nA/cm2 at a reverse bias of 100 V and decrease exponentially with the temperature. Measurement with transient current technique (TCT) shows that electrons have a trapping time of 8 ns. Good spectroscopic result were obtained from both a pad detector and a hybridized Medipix GaAs detector
[en] In this paper we present a novel germanium/gallium arsenide heterostructure X-ray detector with the active volume of germanium. The heterostructure is fabricated by depositing a gallium arsenide layer on a high-purity germanium wafer in a vertical metalorganic vapor-phase epitaxy system. This approach provides a new alternative to traditional lithium diffused n+ contact which is not easily applicable for finely pixelated detectors. The detector chip fabrication utilizing this kind of heterostructure is straightforward and only standard lithographic processes need to be applied. Electrical properties of the small format detector matrices are studied. Very low reverse biased current at 77 K is observed. It is concluded that the diffusion of arsenic in germanium results in an n-type germanium layer under the epitaxial gallium arsenide
[en] Crystal quality of radiation detector-grade TlBr material was analyzed by X-ray diffraction and synchrotron X-ray topography methods. The analyzed TlBr crystals were further processed for electrical characterization and current-voltage characteristics were measured at a temperature range of 210-320 K. The crystals studied in this work were grown by the Bridgman-Stockbarger process. X-ray diffraction measurements show the presence of small-angle grain boundaries in the crystals. The crystal with the most pronounced small-angle boundaries showed the lowest resistivity and the poorest spectroscopic characteristics.
[en] We introduce a zinc diffusion process to fabricate an InAs-based detector matrix using an atmospheric pressure metal-organic vapour-phase epitaxy reactor. Current-voltage characteristics are measured and different diffusion parameters are experimented. Spectral alpha radiation response of the diode is reported. To our knowledge, this is the first time that InAs was used as an alpha particle detector
[en] TlBr is a promising material for gamma-ray detectors; however, it has crystal quality problems originated from the crystal growth itself and further treatments during detector fabrication. The effect of technological improvements on crystal quality has been studied in this work. Low performance of studied detectors was shown to be associated with residual stress or/and small-angle grain boundaries in these crystals. Several crystals failed as detectors were proved to contain impurities.
[en] Crystal defects of GaAs thin films deposited by metalorganic vapour phase epitaxy on high-quality Ge substrates are studied by synchrotron X-ray topography. The GaAs thin films were measured to have ∼500 dislocations cm-2, which is a similar number to what plain Ge substrates show. The dislocation densities measured are also smaller than, for instance, those of high-quality vapour pressure controlled Czochralski grown GaAs wafers, which typically have dislocation densities of ∼1500cm-2. The GaAs films grown on both sides of two-sided substrates display very good crystal quality throughout the sample