Lead halide perovskite nanocrystals of the formula CsPbBr₃ have recently been identified as potential time taggers in scintillating heterostructures for time-of-flight positron emission tomography (TOF-PET) imaging thanks to their ultrafast decay kinetics. This study investigates the potential of this material experimentally. We fabricated CsPbBr₃ thin films on scintillating GGAG:Ce (Gd_2.985Ce_0.015Ga_2.7Al_2.3O₁₂) wafer as a model structure for the future sampling detector geometry. We focused this study on the radioluminescence (RL) response of this composite material. We compare the results of two spin-coating methods, namely the static and the dynamic process, for the thin film preparation. We demonstrated enhanced RL intensity of both CsPbBr₃ and GGAG:Ce scintillating constituents of a composite material. This synergic effect arises in both the RL spectra and decays, including decays in the short time window (50 ns). Consequently, this study confirms the applicability of CsPbBr₃ nanocrystals as efficient time taggers for ultrafast timing applications, such as TOF-PET.

InGaN/GaN structures are studied as potential candidates for superfast scintillation detectors and show the leading decay time of around 1 ns and intense luminescence.

The influence of dislocation density on the transport properties of high electron mobility transistor (HEMT) structures is reported in this work. Experimental results, obtained on HEMT structures prepared in the same growth run on templates with different dislocation densities, are compared. However, the direct comparison of structures is complicated, since parallel parasitic currents through deeper parts of the heterostructure were observed in samples with lower dislocation density. To suppress this phenomenon, the addition of an AlGaN back barrier (BB) beneath the two dimensional electron gas (2DEG) channel is proposed and optimized and the most suitable design based on both modeling and experimental results is suggested. Subsequently, the comparison of electron mobility in 2DEG for structures with AlGaN BB and different dislocation densities was possible. We show experimentally that lowering the dislocation density considerably increases the electron mobility in 2DEG. It is shown that the dislocation density also has a significant influence on the Fermi level position in GaN. The presented results suggest that reduction of dislocation density can improve the performance of high-frequency GaN HEMT applications.

A set of GaN layers prepared by metalorganic vapor phase epitaxy under different technological conditions (growth temperature carrier gas type and Ga precursor) were investigated using variable energy positron annihilation spectroscopy (VEPAS) to find a link between technological conditions, GaN layer properties, and the concentration of gallium vacancies (V_Ga). Different correlations between technological parameters and V_Ga concentration were observed for layers grown from triethyl gallium (TEGa) and trimethyl gallium (TMGa) precursors. In case of TEGa, the formation of V_Ga was significantly influenced by the type of reactor atmosphere (N₂ or H₂), while no similar behaviour was observed for growth from TMGa. V_Ga formation was suppressed with increasing temperature for growth from TEGa. On the contrary, enhancement of V_Ga concentration was observed for growth from TMGa, with cluster formation for the highest temperature of 1100 °C. From the correlation of photoluminescence results with V_Ga concentration determined by VEPAS, it can be concluded that yellow band luminescence in GaN is likely not connected with V_Ga; additionally, increased V_Ga concentration enhances excitonic luminescence. The probable explanation is that V_Ga prevent the formation of some other highly efficient nonradiative defects. Possible types of such defects are suggested.

The performance of cerium-doped Y ₃ Al ₅ O ₁₂ (Ce ³⁺ :YAG) often depends on cerium solubility achievable in a particular preparation technology.