Thick, high-purity semi-insulating (SI)homoepitaxial layers on Si-face 4H-SiC weregrownsystematically, with resistivity 10

Co-doping Lu 2 SiO 5 :Ce (LSO:Ce) with Ca divalent cations changes the scintillation properties of the crystal. In the present work an influence of Ca 2+ co-doping on energy resolution, light output and non-proportionality was investigated for samples with 0, 0.1, 0.2, 0.3, and 0.4 atomic percent Ca with respect to Lu. A substantial improvement of energy resolution in the co-doped crystals was found and higher light output by about 10% was observed. The best energy resolution of 7.35 0 15% was measured for LSO with 0.2% Ca. Contrary to our expectations, the change in the measured energy resolution of Ca 2+ co-doped LSO samples is not reflected in the non-proportional characteristic of the studied crystals as the non-proportionality curves are independent of Ca concentration. Possible explanations of the underlying mechanism of improving the energy resolution include afterglow suppression via Ca co-doping. Earlier studies showed that calcium co-doping significantly reduces the trap population, hence the decay time of LSO is shortened and the afterglow is substantially quenched. In the current work, the integrated afterglow intensities as well as the afterglow effective decay times correlate with the concentration of Ca 2+ . Since the afterglow was measured about 30 ms after the crystal was irradiated by a strong X-ray source, the integral intensity does not include the faster components of afterglow. Hence, the correlation between afterglow intensity and energy resolution treated in this work is very preliminary.Index Terms-Afterglow, energy resolution, Lu 2 SiO 5 , lutetium oxyorthosilicate, non-proportionality.

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High-resolution photoinduced transient spectroscopy has been applied to study grown-in defect centres in semi-insulating InP:Fe. The defect structure of crystals characterized by various values of Hall mobility has been compared. A number of defect centres with activation energies ranging from 10 to 640 meV were detected. They include shallow donor and acceptor impurities, native defects, shallow impurity–native defect complexes and iron-related defects. It was found that the Hall mobility is mainly affected by the shallow donor concentration which determines the ratio [Fe2+]/[Fe3+]. The electron lifetime is determined either by the iron concentration or the concentration of shallow impurities.

Parameters of electrically active defect centres in vanadium-doped 6H silicon carbide (6H-SiC:V) were investigated by means of the photoinduced transient spectroscopy (PITS) and modulated photocurrent (MPC) method. After a short description of the two techniques, experimental results are presented and briefly compared. Our aim is mainly to understand and explain these experimental results. In particular, in the PITS technique a shallow level seems to be at the origin of negative photoconductivity. Besides, in the same temperature range hole and electron levels can be detected at the same time. Finally, the detection of a given level seems to depend on the photon flux used to perform the PITS experiment. As far as the MPC experiment is concerned, it has put into evidence a very efficient shallow level. A numerical calculation was developed to simulate both experiments in order to understand the experimental results. By means of this simulation, we have explained all the phenomena observed experimentally in each technique and we propose a simple model for the distribution of electrically active defect centres in 6H-SiC:V crystals.