Room temperature semiconductor detectors provide high energy resolution in gamma-ray spectroscopic applications, such as radioisotope identification. Materials such as TlBr and CsPbBr3, which provide ~2% FWHM, or better, energy resolution for 662-keV photopeak from Cs-137 irradiation at room temperature and high stopping power, nevertheless exhibit mixed electronic and ionic conduction that can lead to undesirable performance degradation. While the charge pulses generated by the gamma-ray interaction and a component of the leakage current are composed of a dominant electronic signal, the ionic component contributes to the current. It affects device stability via the migration of ionic species under applied bias and polarization at the semiconductor-electrode interface, interfering with charge collection. In this work, we characterize electronic and ionic conduction in single-crystal devices of TlBr and CsPbBr3 (CLB) using ionically blocking electrodes. The ionic contribution to the leakage current is evaluated from the devices' impedance spectra. In contrast, the electronic contribution is extracted from the asymptotic limit of the devices' current-voltage-time (iVt) plots for different bias values. The response to illumination with a 375-nm LED is also measured in the iVt plots. This work presents expressions for the temperature dependence of the conductivity, referencing previous work for TlBr. It also presents the gamma-ray spectra's bias dependence and evaluates ionic conduction's role in device burn-in, conditioning, and aging processes. Comparing the impedance spectra with and without LED illumination confirms that ions represent the majority charge carrier at room temperature for TlBr and CLB, which is consistent with previous work.
Optical properties of ferroelectric BaTiO3 (BTO) and paraelectric SrTiO3 (STO) multilayer structures were investigated
as a possible material choice for thin-film electro-optic devices. It has been demonstrated that dielectric properties can be
enhanced by optimizing the stacking periodicity of BTO-STO superlattices, and in this work, it was studied how the
shifts in permittivity are transferred to the optical properties. BTO-STO superlattices with stacking periodicity varying
between 27 Å and 1670 Å were grown on MgO substrates by pulsed laser deposition. In x-ray diffraction patterns,
periodic satellite peaks were observed indicating the formation artificial superlattices. The evolution of electro-optic
response with varying stacking periodicity was analyzed by ellipsometric transmission method. The electro-optic
response reached a maximum at a stacking periodicity of 105 Å corresponding the individual layer thickness of 13 unit
cells. The suitability of superlattices, and also single layer BTO thin films, in planar optical devices were evaluated by
fabricating and characterizing Mach - Zehnder waveguide modulators.
We examine the luminescent properties of cerium-doped yttrium aluminum garnet (Ce:YAG)
under cathodoluminescence. The cerium emission is strongly affected by the presence of intrinsic
defects it the crystal. We show that a model based on non-radiative energy transfer is compatible
with the results obtained from cathodoluminescence exreriments.
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