Optical and THz investigations of mid-IR materials exposed to alpha particle irradiation

Abstract

The paper is the first comprehensive study on alpha particle irradiation effects on four mid-IR materials: CaF2, BaF2, Al2O3 (sapphire) and ZnSe. The measurements of the optical spectral transmittance, spectral diffuse reflectance, radioluminescent emission, terahertz (THz) spectral response, transmittance, absorbance, refractive index, real and imaginary parts of the dielectric constant and THz imaging are used as complementary investigations to evaluate these effects. The simulations were run to estimate: (i) the penetration depth, (ii) the scattering of alpha particle beam, (iii) the amount of material affected by this interaction, and (iv) the number of vacancies produced by the radiation exposure for each type of material. The simulation results are compared to the off-line measurement outcomes. The delay and spectral composition change of the reflected THz signal highlight the modification induced in the tested materials by the irradiation process.

Effect of ZnO Addition and of Alpha Particle Irradiation on Various Properties of Er3+, Yb3+ Doped Phosphate Glasses

“…Similar decreases in the transmission after alpha particles irradiation were reported in different materials such as CaF 2 , Al 2 O 3 or ZnSe due to the formation of color centers [9]. The absorption coefficients in the visible wavelength range of the Er 3+ 4f-4f transitions also decrease after irradiation indicating that the irradiation has a significant impact on the Er 3+ ions sites.…”

“…Radiation hardening tests are of interest in relation to specific space missions, as ionizing radiation originating outside of Earth's atmosphere is constituted by 87% of protons, 12% of alpha particles and 1% of heavy elements. Recently, we reported, for the first time, a comprehensive study on alpha particle irradiation effects on four mid-IR materials [9] and gamma-ray-induced changes in Bi/Er co-doped optical fibers [10]. Our investigations brought several novelties to the field of material research operating in harsh environments (i.e., ionizing radiation) and in the use of THz spectroscopy and imaging in the evaluation of irradiated optical materials.…”

Bulk Barrier Source-Gated Transistors with Improved Drain Current Dynamic Range and Temperature Coefficient

“…This is due to a softer barrier and the pronounced effect of the gate electric field on the barrier height (10,11) and should lead to increased switching speed compared to the SBSGT. SBSGT output characteristics show the typical low-voltage saturation due to source pinch-off (1-6) and very low drain voltage dependence of the saturated current, facilitated by the presence of a field relief structure in the source contact metallization (4)(5).…”

“…Source-gated transistors (SGTs) (1-3) are thin-film devices with flat output curves, low saturation voltage, and tolerance to process variations, suitable for both analog (4) and digital circuits (5). Operation relies on a depletion region formed at the source, which deliberately comprises a potential barrier.…”

“…This source barrier is usually realized as a metal-semiconductor contact -Schottky Barrier SGT (SBSGT) and these devices usually have modest barrier lowering (drain current modulation) related to the electric field dependence of the Schottky barrier height. SBSGTs have been studied various material systems, including a-Si:H (2, 3, 6), poly-Si (4,5), ZnO (7) and semiconducting polymers (8).…”