Low-dimensional, lead-free halide perovskites are promising candidates for next-generation radiation detectors due to their favorable optoelectronic properties and environmental safety. Among them, Cs3Bi2Br9 has thus attracted significant attention for its layered structure and intrinsic stability. Although Cs3Bi2Br9 has already been explored for X-ray detection, simple and scalable fabrication routes for its thin films on flexible low-cost substrates remain underdeveloped. Here, we demonstrate a sustainable, all-dry abrasion method to directly deposit Cs3Bi2Br9 thin films onto biodegradable office-grade printing paper at room temperature, enabling the fabrication of flexible, lead-free X-ray detectors. The resulting devices exhibit a resistivity of 6.9 × 109 Ω cm and a mobility-lifetime (μτ) product of 9.07 × 10−4 cm² V⁻¹, yielding X-ray detection sensitivities of 660–860 μC Gyair⁻¹ cm⁻². Reducing the electrode spacing to 50 μm further enhances sensitivity to ~28,000 μC Gyair−1 cm−2 which is one of the largest values that reported for thin film-based X-ray detectors, indicating strong potential for miniaturized applications. In addition to high sensitivity, the devices deliver effective imaging performance with a spatial resolution of 1.0 lp/mm (with 28 cm between X-ray source and detectors) and retain stable operation after more than 30 days of air exposure. This work introduces a green and scalable platform for developing high-performance, lead-free, and environmentally sustainable X-ray detectors.

Cadmium telluride (CdTe) remains a leading semiconductor material for room-temperature high-energy radiation detection. Despite advances in single-crystal growth that have pushed CdTe's resistivity near its intrinsic limit, detectors still suffer from current noise under high bias. Schottky contacts or p-n junctions are commonly used to suppress leakage current while preserving charge transport, but their performance in bulk CdTe is hindered by strong Fermi-level pinning. We demonstrate a van der Waals (vdW) contact integration approach that mitigates Fermi-level pinning and significantly reduces dark current. This study presents a novel approach to enhancing Schottky-type X/ $\gamma $ -ray detectors based on semi-insulating CdTe crystals using vdW contacts. Gold (Au) electrodes were mechanically transferred onto CdTe surfaces to minimize surface damage and mitigate Fermi-level pinning. Cross-sectional transmission electron microscopy (TEM) confirms the absence of atomic intermixing at the Au-CdTe interface, validating the noninvasive nature of the vdW contact. In contrast, Au contacts deposited by evaporation show residual contamination, as revealed by X-ray photoelectron spectroscopy (XPS), along with increased defect states confirmed by low-temperature photoluminescence (PL). For mechanically transferred contacts vdW, both XPS and PL spectra closely match those of pristine CdTe, indicating minimal surface degradation. This improved interface quality correlates with an increase in the Schottky barrier height (SBH) from 0.78 to 0.82 eV. As a result, Au/CdTe/Au detectors with vdW contacts exhibit reduced dark current and improved energy resolution (from 14.4% to 11.8%) for 59.5-keV $\gamma $ -rays from a Am-241 isotope. These findings demonstrate the potential of vdW contact engineering to significantly improve the performance of CdTe-based radiation detectors.

The In/CdTe/Au, Al/CdTe/Au, Cr/CdTe/Au, Ti/CdTe/Au, Ni/CdTe/Au, and Au/CdTe/Au X/gamma-ray sensors were fabricated using Ar plasma surface processing of detector-grade CdTe(111) crystals. The energy resolutions estimated from the Am-241 and Cs-137 isotope spectra, as well as dark currents at reverse bias voltages of 100-1500 V (increasing in steps of 100 V) were measured to monitor the sensor operation stability. For "freshly" made ohmic-type Au/CdTe/Au structures, the maximum voltage to maintain relatively moderate dark currents (5-7 nA) was similar to 500 V. For the other (barrier) structures, the dark currents at 500 V did not exceed 1.5 nA and increased almost linearly up to 3-4 nA at 1500 V. The best resolutions were observed at 100-200 V and 700-1000 V, respectively: 6.7-7.5%@59.5 keV for the barrier structures, 8.4-9.2%@59.5 keV for Au/CdTe/Au samples, and 0.9-1.1%@662 keV for all sensors (except Au/CdTe/Au). The time-dependent features of the I-V characteristics of ohmic and barrier structures were discussed. After 24 months of storage, the dark currents of almost all sensors decreased by 10-15% and the energy resolutions of the Am-241 and C-137 spectra did not change or slightly improved.

A comparative analysis of the Cs-137 isotope spectra measured both by single and series-connected Cr/CdTe/Au diodetype X/gamma-ray detectors has been conducted. Rectifying (Cr) and ohmic (Au) contacts were respectively formed on the B-and A-faces of detector-grade CdTe(111) crystals after Ar plasma surface processing. The diode sandwiches (stacks) were created by staking and connecting in series two Cr/CdTe/Au Schottky diodes with similar parameters. A key feature of the Cs-137 isotope spectra obtained from these sandwiches was the presence of two peaks with maxima and energy positions (channel numbers) depending on the CdTe crystal thickness and relative positions of the diodes in the sandwich. The sum of channel numbers corresponding to these peaks equaled the channel number of the peak in the spectrum obtained by a single diode. Even when Cr/CdTe/Au diodes of different thicknesses were used in the sandwich, the sum of the channel numbers corresponding to two peaks in the Cs-137 spectra remained constant. The heights (maxima) of the two peaks were much higher than the peak height the spectrum measured by a single diode. The series-connected Cr/CdTe/Au Schottky diodes detected X/gamma-rays much more effectively than a single detector at a bias voltage equal to half that applied to the sandwich. Another advantage of the diode sandwiches was the time stability of their characteristics. The Cs-137 isotope spectrum degraded during 8 hours of measurement by a single detector, while no noticeable changes were found in detection efficiency and energy resolution when the sandwich detectors were used.

A technique has been developed for determining the linear tension of steps with one-ion and two-ion heights that form growth/evaporation spirals on NaCl(100). This technique is based on the interpretation of experimentally obtained nonlinear dependences of the steady-state distance between spiral’s turns in relation to the inverse undersaturation by numerical simulation performed using the analytical solution of the Barton, Cabrera, and Frank diffusion problem, taking into account the step kinetic coefficient and the back stress effect. The linear tension value of steps with one-ion height is found to be less than half the linear tension value of steps with two-ion height. This suggests that the studied vicinal surfaces are thermodynamically stable. The proposed technique can also be applied to other alkali halide crystals.

The Ni/CdTe/Au Schottky diode X/γ-ray sensors, fabricated using the Ar-ion bombarding technique, exhibit low leakage current density ( 20 nA/cm2 at 1000 V) and high energy resolution ( 1.0

Though CsPbBr3 single crystals (SCs) possess intriguing photoelectronic properties for x/γ-ray detection, the serious ion migration and high thermally activated carrier concentration at room temperature (RT), typically associated with defect states in CsPbBr3 crystals, result in a high dark current and drift of baseline, hindering their potential applications. In this investigation, liquid nitrogen cooling is proposed to freeze deep-level defects in CsPbBr3 SCs, thereby suppressing the ion migrations and decreasing the thermally excited carrier concentration. Utilizing photoluminescence (PL) and time-resolved PL spectra, coupled with theoretical models for photoexcitation and photoemission processes, the freezing of deep-level defects at liquid nitrogen temperature (LNT) is confirmed, which is conducive to decreasing non-radiative recombination. At LNT, the CsPbBr3 SC exhibits a higher resistivity of 4.95 × 1011 Ω cm and a higher mobility–lifetime product of 9.54 × 10−3 cm2 V−1, in contrast to the RT values of 3.86 × 109 Ω cm and 3.67 × 10−3 cm2 V−1, respectively. Furthermore, the x-ray detector at LNT exhibits a high sensitivity of 9309 μC Gyair−1 cm−2 and an impressively low detection limit of 0.054 nGy s−1, which offers a route for obtaining highly sensitive x-ray detectors for applications including ultra-low dose radiation imaging.

When creating a Schottky contact to suppress the leakage current of semiconductor gamma-ray detectors and improve their energy resolution, it is successfully employed the fact that the formation of a Schottky barrier is determined not only by the difference in the electrode and semiconductor work functions but also affected by the semiconductor surface state. Oxygen plasma (OP) treatment has been used to modify the surface states of CdSe single crystals (SCs) prior to the Au electrode deposition, thereby creating a Schottky contact at the metal-semiconductor interface. The n-type Schottky contact formation has been confirmed by the I-V characteristics and ultraviolet photoelectron spectroscopy analysis. X-ray photoelectron spectroscopy has shown that the stoichiometric state of the CdSe SC surface changes from a Cd-deficient (untreated surface) to a near-ideal stoichiometric (OP-treated surface). In addition, a newly formed CdSeO3 component has been revealed, which is beneficial for suppressing the surface leakage current. The Au/CdSe/Au radiation detector with the single-sided OP-treated surface (Schottky diode) exhibits a higher energy resolution of (23.93 +/- 0.89)% for 241Am 59.5 keV gamma-rays compared to that of the detectors without surface treatment ((44.66 +/- 2.25)%). The energy resolution of the champion CdSe-based Schottky diode type gamma-ray detector for 241Am 59.5 keV gamma-rays can reach 22.72%.

Precisely controlling the amount and location of PbI2 in a lead halide perovskite light absorption layer is crucial for improving the performance of perovskite solar cells (PSCs) by utilizing the passivation effect of PbI2. Based on the high absorption coefficient of perovskite materials and the resulting extremely shallow UV penetration depth, a non-contact approach of the precise preparation of a PbI2 passivation layer based on excimer laser irradiation (ELI) is proposed. 248 nm KrF excimer laser is adopted to irradiate the surface of [(FAPbI3)0.87(MAPbBr3)0.13]0.92[CsPbI3]0.08 film, and a PbI2 passivation layer could be obtained on the surface of the triple cation perovskite film through the partial decomposition of the surface layer of perovskite films induced by ELI process. And then, the average power conversion efficiency of the PSCs has been increased obviously from 17.82% to 20.68%. This non-contact photonic approach successfully breaks through the bottleneck of precisely preparing PbI2 passivation layer and is expected to contribute to the further development of perovskite based devices.

The electrical characteristics of CdTe-based surface barrier structures, which can be used as spectroscopic X/γ-ray detectors, have been investigated. The metal-semiconductor structures were obtained by thermal (resistive) vacuum deposition of various metals onto detector-grade CdTe crystals. Metals with different work functions, such as Al, In, Ni, Ti, Cr, and Au, were employed as electrode materials for rectifying contacts. An ohmic contact was created on the entire opposite surface of the crystals by chemical deposition of Au from a gold chloride solution. The surface processing of CdTe crystals before the formation of both rectifying and ohmic contacts included mechanical and chemical polishing, as well as Ar-ion bombardment. Dark currents at reverse voltage of 1500 V did not exceed 4 nA for all the diodes except for the Au/CdTe/Au structure. The effect of the metal nature on the I-V characteristics and charge carrier transport mechanisms was studied, and the features of voltage dependences of dark current were explained by differences in the work functions of the metals, as well as the contact deposition technique.

Owing to the large x-ray attenuation coefficient, appropriate bandgap, high resistivity, and high mobility-lifetime (μτ) product, binary II–VI semiconductor CdSe is a promising x-ray detection material and it has exhibited excellent x-ray detection at room temperature (RT). For further improving the characteristics of CdSe x-ray detectors, the electrical properties of CdSe single crystals (SCs) grown through the pressure-assisted vertical Bridgman method and their x-ray detection performance have been investigated at RT and liquid nitrogen temperature (LNT), respectively. The significantly enhanced x-ray photocurrent and the prolonged response time of the devices operating at LNT indicate the photogenerated carrier lifetime could be increased by the enhanced trapping–detrapping effect obviously, and the μτ product of CdSe SCs increases from 1.39 × 10−5 to 5.34 × 10−4 cm2 V−1 with temperature lowering from RT to LNT. Meanwhile, an ultrahigh sensitivity of 5.24 × 106μC Gyair−1 cm−2 and an extremely low detection limit of 3.68 nGyair s−1 have been acquired by the CdSe SC based x-ray detectors at LNT, which is 140 times higher and 5.8 times lower than it has been at RT. Compared with conventional semiconductor x-ray detectors, the ultra-high sensitivity and extremely low detection limit of CdSe SC based detectors make their application prospects very promising.

The Schottky-diode X/.. -ray detectors based on semi-insulating p-like CdTe single crystals with four values of uncompensated impurity concentration (N approximate to 2 x 10(12) cm(-3), 2 x 10(11) cm(-3), 1 x 10(11) cm(-3), 4 x 10(10) cm(-3)) were developed and characterized by I-V measurements at low reverse bias (0.005-100 V) and detection of Cs-137 and Am-241 radioisotope emission spectra. All the detectors were fabricated by the same technique using vacuum evaporation of a Cr electrode (rectifying contact) and chemical deposition of an Au electrode (Ohmic contact) onto the B- and A-face of CdTe(111) crystals, respectively, pre-treated with Ar-ion bombardment. The change of the charge transport mechanism from over-barrier (thermionic) to generation current along with the analysis of the temperature dependence of the differential resistivity evidenced a high concentration of deep level impurities near the middle of the semiconductor bandgap. The detection efficiency eta of the detectors was calculated using the corrected expressions for the coordinate dependence of the electrical field strength in a diode which took into account the fact that the depletion region width exceeded the CdTe crystal thickness at higher bias voltages. It was shown that the dependence eta(N) decreased with increasing N without a maximum corresponding to an optimal value N-opt as reported earlier. The Cr/CdTe/Au Schottkydiode detectors, fabricated using CdTe with the lowest N, demonstrated the highest energy resolution (0.6% @662 keV and 7.5% @59.5 keV) and it degraded when crystals with higher N were used.

The In/CdTe/Au p-n junction-diode X/γ-ray detectors, formed by frontside laser irradiation doping, were studied using IV characteristics, measured at different temperatures, and spectra of 241Am, 57Cs, and 137Cs isotopes, obtained in a wide bias range V = 60-380 V. A key feature of the technology was low-temperature ( ~90 ºC) vacuum annealing of polished in a Br-methanol solution detector-grade (111) oriented p-like CdTe crystals prior to the deposition of an In dopant film and formation of electrodes. After laser-induced doping of a layer near the In/CdTe interface and deposition of an Au electrode (ohmic contact), the In/CdTe/Au structures showed high rectification. The I-V measurements and calculations revealed that the dominant charge transport mechanism at low reverse bias was generation-recombination in the space charge region. It was noteworthy that the reverse current linearly increased at higher V ≥ 50 V when the depletion region extended over the entire crystal thickness. A sharp increase in I at higher V, that was inherent in diode structures (I ~ V n , n < 1), was not observed that evidenced a perfect ohmic contact, i.e. no injection of minority carriers from the Au/CdTe contact occurred. The detectors formed on the preliminary annealed CdTe crystals showed high energy resolution ((FWHM = 0.99 %@662keV at V = 300 V). Furthermore, high spectroscopic characteristics (detection efficiency, energy resolution, true energy position of the 662 keV peak) were observed (with a deviation < 20 %) at V =150-400V.

The conditions for occurrence of convective mass transfer in a liquid inclusion located in a thermally stressed crystal have been investigated. An estimated calculation of the Rayleigh number for a convective cell with solid boundaries has been performed. It is shown that the calculated value of the Rayleigh number can exceed the critical value. For such conditions, we have obtained analytical expressions for the perturbed velocity and temperature of a cylindrical convective cell with solid boundaries that exist in the inclusion. The theoretical model of induced transitions of atoms of the crystal matrix into solution and back is proposed, taking into account convective mass transfer. Based on the proposed model, the analytical expressions for the dependence of the inclusions velocity on their size at low and high temperature gradients have been obtained. A good quantitative correspondence between the theoretical model and the experimental data is shown in both cases.

The morphology of the growth surface near NaCl(100), formed during the pore motion in a crystal due to the temperature gradient, has been studied by the electron microscopic method of vacuum decoration. It is shown that at T = 950 K and ∆μ/kT = 4·10-3, the profile of the vicinal surface in the <11> direction is represented by monoatomic steps, while in the <10> direction, as the surface curvature increases, there is a grouping of steps with the formation of macrosteps – bunches of elementary steps separated by areas of atomically smooth terraces. The sawtooth dependence of the step density on the longitudinal coordinate is described by a particular solution of the Burgers equation for a shock wave. Data on the parameters of three shock waves and the time of their formation are obtained.

The fabricated In/p-CdTe/Au diode structures with Schottky (In/p-CdTe) and quasi-ohmic (Au/p-CdTe) contacts were transformed into p-n junction diodes by applying the developed frontside laser irradiation doping technique. The Schottky diodes with In and Au electrodes (both with thickness of 400 nm), deposited on the chemically pre-treated B-and A-face of the detector-grade CdTe(111) single crystals, respectively, were subjected to multiple (from tens to thousands times) irradiation from the In film side with series of nanosecond pulses of a KrF excimer laser. As a result of such irradiation, a thin heavily doped n-type CdTe:In layer was formed, a shallow abrupt p-n junction was created and thus the In/CdTe/Au Schottky diode was transformed into the In/CdTe/Au p-n junction diode. The temperature distributions in the In/CdTe/Au structure under laser irradiation were calculated and the I-V characteristics of the diodes were measured for different energy densities E and number N of laser pulses, respectively. The processes of frontside laser irradiation doping and carrier charge transport mechanisms in the created In/CdTe/Au p-n junction diodes were discussed. The samples with higher performance were obtained when only a part of the In electrode thickness was melted during a single laser action (E ~& nbsp;110 mJ/cm(2)) and repeated (N ~& nbsp;300-500) irradiation was employed. The fabricated In/CdTe/Au p-n junction-diode structures with relative low reverse dark currents (~& nbsp;20-50 nA/cm(2)) were quite sensitive to X/gamma-rays and demonstrated sufficient ability to detect the emission of Am-241, Co-57, and Cs-137 isotopes. It has been shown that applying the frontside laser irradiation doping technique to In/CdTe/Au structures, it is possible to transform Schottky diodes with low characteristics into highly rectifying In/CdTe/Au p-n junction diodes which are X/gamma-ray detectors with moderate or even high detection parameters.

The electrical and spectroscopic characteristics of the ionizing radiation detectors, designed as Ti/CdTe/Au diodes with a rectifying barrier were investigated. Schottky (Ti/CdTe) and ohmic (Au/CdTe) contacts were formed on the B- and Afaces of detector-grade p-CdTe(111) crystals subjected to Ar plasma treatment. Owing to the advantages of the fabrication technique, the Ti/CdTe/Au Schottky-diode X/γ-ray detectors with similar parameters were obtained. The features of the single detector and stacks of two mounted detectors, connected in parallel or series, were analyzed. The measurements of the I-V characteristics showed that the sensor, consisting of two series-connected detectors, has lower dark current and significantly the weakened effect of space-charge-limited currents (SCLC) than the single detector or two parallel-connected detectors. The stack of the detectors connected in parallel has higher photosensitivity but lower energy resolution compared with those characteristics of the single detector. The analysis of the emission spectra of 137Cs and 241Am isotopes, measured at room temperature, showed that the sensitivity of the stack of the series-connected detectors turned out to be the highest. However, the double peaks were observed in the isotope spectra taken with such detector stack that was unusual and attributed to features of the electronic signal processing. Series connection of detectors has the advantages as reducing the dark current and decreasing the stack capacitance. To implement these features and optimally use such connection, specific electronic devices are needed, in particular to combine two charge packets which are formed by the detector stack into one with a larger amplitude.