Hans Kraus

Abstract:

Applications that utilize scintillation detectors at low temperatures are growing in number. Many of these require materials with high light yield and a fast response. Here we report on the low-temperature characterisation of ZnSe doped with Al or Te, respectively. The X-ray luminescence and decay curves were measured over the 77–295 K temperature range, and alpha particle excitation was used to examine scintillation light output and decay kinetics over the range 9–295 K. A significant improvement of the scintillation characteristics was observed at cooling below 100 K. The scintillation light yield of the crystals increases by a factor about two, and the decay time constant decreases by almost an order of magnitude to 0.3–0.4 μs. These improvements enhance the potential of ZnSe-based crystals for application in cryogenic scintillation detectors of ionising radiation.

Abstract:

Semiconducting polycrystalline thin films are cheap to produce and can be deposited on flexible substrates, yet high-performance electronic devices usually utilize single-crystal semiconductors, owing to their superior charge-carrier mobilities and longer diffusion lengths. Here we show that the electrical performance of polycrystalline films of metal-halide perovskites (MHPs) approaches that of single crystals at room temperature. Combining temperature-dependent terahertz conductivity measurements and ab initio calculations we uncover a complete picture of the origins of charge-carrier scattering in single crystals and polycrystalline films of CH3NH3PbI3. We show that Fröhlich scattering of charge carriers with multiple phonon modes is the dominant mechanism limiting mobility, with grain-boundary scattering further reducing mobility in polycrystalline films. We reconcile the large discrepancy in charge-carrier diffusion lengths between single crystals and films by considering photon reabsorption. Thus, polycrystalline films of MHPs offer great promise for devices beyond solar cells, including light-emitting diodes and modulators.