Context.Space weathering is a process that changes the surface of airless planetary bodies. Prime space weathering agents are solar wind irradiation and micrometeoroid bombardment. These processes alter planetary reflectance spectra and often modify their compositional diagnostic features.Aims.In this work we focused on simulating and comparing the spectral changes caused by solar wind irradiation and by micrometeoroid bombardment to gain a better understanding of these individual space weathering processes.Methods.We used olivine and pyroxene pellets as proxies for planetary materials. To simulate solar wind irradiation we used hydrogen, helium, and argon ions with energies from 5 to 40 keV and fluences of up to 10¹⁸particles cm⁻². To simulate micrometeoroid bombardment we used individual femtosecond laser pulses. We analysed the corresponding evolution of different spectral parameters, which we determined by applying the Modified Gaussian Model, and we also conducted principal component analysis.Results.The original mineralogy of the surface influences the spectral evolution more than the weathering agent, as seen from the diverse evolution of the spectral slope of olivine and pyroxene upon irradiation. The spectral slope changes seen in olivine are consistent with observations of A-type asteroids, while the moderate to no slope changes observed in pyroxene are consistent with asteroid (4) Vesta. We also observed some differences in the spectral effects induced by the two weathering agents. Ions simulating solar wind have a smaller influence on longer wavelengths of the spectra than laser irradiation simulating micrometeoroid impacts. This is most likely due to the different penetration depths of ions and laser pulses. Our results suggest that in some instances it might be possible to distinguish between the contributions of the two agents on a weathered surface.

We investigated the feasibility of long-drift-time CdZnTe (CZT) gamma-ray detectors, fabricated from CZT material produced by Redlen Technologies. CZT crystals with cross-section areas of 5 × 5 mm² and 6 × 6 mm² and thicknesses of 20-, 30-, 40-, and 50-mm were configured as 3D position-sensitive drift detectors and were read out using a front-end ASIC. By correcting the electron charge losses caused by defects in the crystals, we demonstrated high performance for relatively thick detectors fabricated from unselected CZT material.

In this contribution we demonstrate both experimentally and theoretically the possibility to control the profile of internal electric field by compensation of the space charge formed by carriers trapped at deep levels ${\text{Q}}_{\text{T}}$ with space charge present due to band bending at the metal/CdTe interface ${\text{Q}}_{\text{M}}$ . The demonstrated mechanism represents a promising way to decrease the problems associated with charge collection efficiency in CdTe x-ray detectors operated at high fluxes of x-ray photons.

The traditional method for electron lifetime measurements of CdZnTe (CZT) detectors relies on using the Hecht equation. The procedure involves measuring the dependence of the detector response on the applied bias to evaluate the μτ product, which in turn can be converted into the carrier lifetime. Despite general acceptance of this technique, which is very convenient for comparative testing of different CZT materials, the assumption of a constant electric field inside a detector is unjustified. In the Hecht equation, this assumption means that the drift time would be a linear function of the distance. This condition is not fulfilled in practice at low applied biases, where the Hecht equation is most sensitive to the μτ product. As a result, researchers usually take measurements at relatively high biases, which work well in the case of the low μτ-product material, <10⁻³ cm²/V, but give significantly underestimated values for the case of high μτ-product crystals. In this work, we applied the drift-time method to measure the electron lifetimes in long-drift-length (4 cm) standard-grade CZT detectors produced by the Redlen Technologies. We found that the electron μτ product of tested crystals is in the range 0.1–0.2 cm²/V, which is an order of the magnitude higher than any value previously reported for a CZT material. In comparison, using the Hecht equation fitting, we obtained μτ = 2.3 × 10⁻² cm²/V for a 2-mm thin planar detector fabricated from the same CZT material.

In this contribution we introduce a method of deep level spectroscopy in semi-insulating semiconductors demonstrated on detector-grade bulk CdZnTe. The method is based on the measurements of temporal and temperature evolution of the electric field profile in studied samples, which is very sensitive to a change of occupancy of deep levels. The measurement of the electric field is based on the linear electro-optic (Pockels) effect using the InGaAs avalanche photodiode with fast response. The internal electric field profile in studied samples significantly changes under various external conditions represented by the application of the bias and pulsed illumination with below-bandgap light. From the knowledge of the electric field behavior and using a standard analysis based on thermally induced transitions of electrons and holes from the deep levels to the conduction and valence bands, respectively, it is possible to get activation energies of the energy levels, their types (donor or acceptor) and corresponding capture cross-sections. By this method we have found deep levels responsible for the polarization of CdZnTe detector under high photon-fluxes. Identified deep levels E v + 0.41 eV, E v + 0.77 eV and E v + 0.94 eV can capture the photo-generated holes and thus form a positive space charge, which is responsible for polarization of the detector.

We have studied the possibility of above bandgap light induced depolarization of CdZnTe planar radiation detector operating under high flux of X-rays by Pockels effect measurements. In this contribution, we show a similar influence of X-rays at 80 kVp and LED with a wavelength of 910 nm irradiating the cathode on polarization of the detector due to an accumulation of a positive space charge of trapped photo-generated holes. We have observed the depolarization of the detector under simultaneous cathode-site illumination with excitation LED at 910 nm and depolarization above bandgap LED at 640 nm caused by trapping of drifting photo-generated electrons. Although the detector current is quite high during this depolarization, we have observed that it decreases relatively fast to its initial value after switching off the depolarizing light. In order to get detailed information about physical processes present during polarization and depolarization and, moreover, about associated deep levels, we have performed the Pockels effect infrared spectral scanning measurements of the detector without illumination and under illumination in polarized and optically depolarized states.