Lead halide perovskites are promising materials in a wide range of optoelectronic devices. The internal instabilities of perovskites under illumination, however, hinder their application. Here, light-induced changes in CH3NH3PbBr3 single crystals are studied, focusing on charge carrier transport properties and deep defect evolution. Using laser-induced transient current technique measurements under steady-state illumination enables the distinction of electron and hole conductivity. An improvement in charge carrier collection is observed stemming from reduced surface recombination and increased hole lifetime. Surprisingly, despite the overall optimization of carrier transport, the simultaneous formation of deep defects under illumination is recorded via photo-thermal deflection spectroscopy. Empirical models are proposed to rationalize all light-induced changes. The explanations are based on strong electron trapping, ion migration, and passivation of strong recombination centers by light-induced deep defects.

We present a time-domain technique based on rapid bias polarity switching (BiPS) to probe charge transport and near-surface defects in halide perovskite single crystals. The method exploits interfacial extraction barriers, which cause carrier accumulation and subsequent release after bias reversal. BiPS combines surface sensitivity (200 nm-2 μm) with millimeter-scale reach, enabling reconstruction of internal field profiles, detection of bulk space charge down to 10^9 cm^-3, and resolution of microsecond-millisecond trap dynamics. In our setup the surface-state detection limit is 10^9 cm^-2, and could be further improved by optimized illumination and readout. Applied to melt-grown CsPbBr_3 (Cr/Cr) and solution-grown MAPbBr_3 (Cr/SnO_2/Cr), BiPS reveals interfacial barriers that drive hole accumulation and defect filling. CsPbBr_3 shows long-lived space charge (∼ 3× 10^11 cm^-3) and ∼ 250× faster hole extraction than MAPbBr_3, while trap analysis yields capture times of 1-100 μs, detrapping times of 20 μs-3 ms, and activation energies of 300-500 meV. BiPS thus provides direct access to buried interfacial processes, disentangles electronic and ionic contributions, and offers a robust platform for evaluating contacts and guiding defect engineering in perovskite optoelectronic devices.

Chalcogen phosphates of transition metals make up a well-known group of antiferromagnetic semiconductors with the general formula MPX3, where M represents a transition metal and X is a chalcogen, either sulfur or selenium. Most of these compounds adopt a similar structure; however, mercury phosphochalcogenides present an exception with their unique van der Waals layered structure. Transition metal chalcogenides are highly appealing materials for photodetectors due to their exceptional optoelectronic properties. Among them, HgPSe3, a layered van der Waals phosphoselenide, shows promise for photodetection over a broad spectral range, from visible light to X-rays. Despite this, the electronic processes governing its photoresponse remain unclear. In this study, we demonstrate a nanosecond response time of a HgPSe3-based photodetector to visible light and gain deeper insights into the underlying charge carrier dynamics through a comprehensive investigation using complementary time-resolved experimental techniques. Our findings on the role of carrier traps provide a potential pathway for optimizing optoelectronic device performance.

Fourier Transform Photocurrent spectroscopy offers a powerful approach to characterize photodetectors, enabling high-resolution (up to $1 \mathrm{~cm}^{-1}$) measurement of their spectrally resolved photoresponse across various materials. The method allows the detection of very low photocurrents, and it provides valuable information about deep levels in semiconductors and their interband transitions. This study focuses on the photoresponse of semi-insulating SiC of 4 H and 6 H polytypes. In addition, we also show examples of the spectral photoresponse measured using other standard detector materials (CdZnTe and CsPbBr 3 ). Additionally, a responsivity scaling procedure facilitates the evaluation of detector performance. While potential Fourier Transform artifacts and noise from the ambient can occur, these issues are readily addressed. This versatile technique holds promise for further investigation of detector behavior, including temperature dependence and time-resolved dynamics.

Semiconductor hybrid pixel detectors with Timepix-family chips with CdTe pixelated sensors are widely used for the detection of various types of ionizing/non-ionizing radiation in applications ranging from radiography imaging, non-destructive testing, particle radiotherapy to electron microscopy. It is important to achieve a higher long-term stability of the sensor chips and a lower occurrence of overall malfunctions. The polarization of the sensor to which a bias is applied, and the associated deformation of the electric field profile is the main cause of the instability of the detection properties. Better stability of the detector and limitation of the effect of its polarization opens the way to ultra-high-dynamic-range image capture. Results of implementing the pulsing bias voltage method in the MiniPIX detector with CdTe pixelated sensor and the study of stabilization of the degree of polarization by illuminating the sensors using LEDs are shown. A vein-like structure is observed in the image of the detector surface uniformly illuminated by a defocused Gaussian intensity profile laser beam. This structure is identical to that which can be observed under X-ray irradiation. Laser-Induced Transient Current Technique is used to characterize the electric field profile and examine the vein structure in detail by scanning a focused laser beam. We evaluate the time evolution of the electric field profile at the border of the veins and outside to find the difference. Obtained current waveforms in mapping the pixelated detector chip and the distribution uniformity of the collected charge will be shown. The properties of the sensor will also be evaluated when combined with the display readout chips. With the use of the X-ray diffraction method, the causes of the vein-like structure can be more closely identified. The obtained data are also shown.

We demonstrate that the I-V characteristics measured shortly after biasing can be used to distinguish bulk and contact resisitivity in CsPbBr 3 detector with Cr contacts. This technique can be also to determine the drift mobility of the charge carries. We also conducted I-V measurements at various temperatures to determine the contact barrier height. Presented technique will be used to study the equilibrium resistivity in whole crystal ingot along the axis of growth.

Owing to their outstanding optoelectronic properties, halide perovskite (HP) materials have been employed in a wide range of applications, including solar cells, light-emitting devices, and X-ray detectors. Among them, lead-free double HPs are characterized by enhanced stability and reduced toxicity compared with lead-based alternatives. Cs2AgBiBr6, in particular, has emerged as a promising candidate for direct X-ray detection. The detection sensitivity, on the other hand, cannot yet compete with that of lead-containing perovskites. Developing schemes to improve X-ray detection efficiency is critical for reducing radiation exposure in medical imaging applications. Here, we investigate the potential of controlled doping and cation substitution with either lanthanides or small organic cations to improve the X-ray detection performance of Cs2AgBiBr6. Our findings reveal that by growing the perovskite in a slightly Bi-poor and Eu-rich environment, the X-ray sensitivity significantly increases 7-fold (from 17 to 120 μC Gyair -1 cm-2) and simultaneously improves the phototo-dark current ratio (from 2.5 to 29). Additionally, Cs-site substitution with imidazolium remarkably enhances the sensitivity over 10-fold (180 μC Gyair -1 cm-2), and ammonium enhances the phototo-dark current ratio to 37. Terahertz photoconductivity measurements reveal a positive correlation between enhanced X-ray sensitivity and improved charge transport properties (e.g., increased scattering time and, thus, carrier mobility) by doping. This study outlines straightforward strategies for boosting X-ray detection and fundamental photoconductivity in lead-free double HP, with potential implications for broader optoelectronic applications.

CdZnTe is prominent materials investigated due to its excellent ability to directly detect and perform energy-dispersive spectroscopy of high energy radiation with devices operating at room temperature. In spite of significant progress at the material technology and detector manufacture, the bias-induced polarization of Schottky-barrier-type detectors manifested by gradual warping of electric field throughout the detector and depreciation of spectra detected in a steadily biased sensor is still an unresolved problem. In this presentation, we investigate the polarization phenomena in CdZnTe equipped with hole blocking anode, which induces a negative charging in the detector’s bulk. We measure Laserinduced transient currents excited on the cathode side in different bias and a very wide time range $0.1 \mathrm{~ms}-5 \times 10^{4} \mathrm{~s}$ after detector’s biasing. We show that the polarization does not saturate at any specific time. It continuously slows down but proceeds without tendency to the stabilization. The ongoing polarization cannot be explained by a charging of a set of discrete defect levels. We thus propose more complex model of defect structure defining multivalent states positioned near the middle of the band gap. Such states are populated continuously in time with a decreasing detrapping rate of holes depending on the progressive occupation of these states by electrons. Despite very simple model, the theory allowed us to depict both the onset of the polarization and the slope of the charge density v.s. time. We deduce that corresponding defect states could be related with small tellurium precipitates with diameter less than $1 \mu \mathrm{m}$ or with dislocation network. We also discuss possible contribution of such states to the defect self-compensation and the pinning of Fermi energy near the middle of the band gap that is necessary for the formation of stable semi-insulating material in parallel with very low deep level doping.

In this work, we present our results of the single crystal growth of all-inorganic perovskite $\mathrm{CsPbBr}{ }_{3}$ using Bridgman method and preparation of CsPbBr 3 -ray and gamma ray sensors with high-energy resolution. We used polished and etched single crystalline samples for preparation of the radiation sensors applying chromium electrodes with the guard-ring structure. We identified twins or stacking faults defects in our single crystals, which significantly influence the charge transport in prepared sensors. Using guarded pulsed I-V characteristics we evaluated resistivity of as-grown CsPbBr 3 single crystals $\rho=3 \cdot 10^{8} \Omega \mathrm{cm}$ and we found that the surface current is 3 times higher than bulk current. Using pulsed bias laser-induced transient current technique we evaluated hole mobility of $\mu=25 \mathrm{~cm}^{2} \cdot \mathrm{V} \cdot \mathrm{s}^{-1}$ and hole lifetime $\tau=600 \mu \mathrm{s}$ leading to the hole mobility-lifetime product $\mu \tau\gt1.510^{-2} \mathrm{~cm}^{2} \mathrm{~V}^{-1}$, which is value comparable with the highest quality CdZnTe sensors. We irradiated prepared CsPbBr 3 sensors by X-ray radiation (8 keV) in the switch on/off mode and measured time evolution of the photocurrent density. We found that prepared single crystals are suitable for the fabrication of photocurrent non-spectroscopic sensors. Simultaneously, we observed strong and fast polarization of prepared sensors at DC bias, which does not yet allow using material for preparation of spectroscopic sensors operating at DC bias. The polarization is most probably caused by a non-optimal metallization or the existence of crystallographic defects and high concentration of shallow acceptors in the sensor material. In the presentation, we will demonstrate the effect of various types of metallization and purification of prepared single crystals on the charge collection efficiency of DC biased sensors.

In polarizable materials, electronic charge carriers interact with the surrounding ions, leading to quasiparticle behavior. The resulting polarons play a central role in many materials properties including electrical transport, interaction with light, surface reactivity, and magnetoresistance, and polarons are typically investigated indirectly through these macroscopic characteristics. Here, noncontact atomic force microscopy (nc-AFM) is used to directly image polarons in Fe2O3 at the single quasiparticle limit. A combination of Kelvin probe force microscopy (KPFM) and kinetic Monte Carlo (KMC) simulations shows that the mobility of electron polarons can be markedly increased by Ti doping. Density functional theory (DFT) calculations indicate that a transition from polaronic to metastable free-carrier states can play a key role in migration of electron polarons. In contrast, hole polarons are significantly less mobile, and their hopping is hampered further by trapping centers.

Metal halide perovskites with APbX 3 crystal structure show rapidly increasing global interest as a new generation of radiation detection materials alternative to CdZnTe. In this work, we present our results of the multiple single crystals growth of all-inorganic perovskite CsPbBr 3 using Bridgman method. Crystals were prepared directly from CsBr and PbBr 2 starting materials mixed with a various mole ratio. Our optimized growth process produces crystals with diameter 15 mm and length over 50 mm. We found that the quality of grown single crystals strongly depends on the purity of the starting materials, dropping speed of the growth ampule and cooling rate after growth. For characterization of transport properties of as-grown samples, we used pulsed I-V characteristics, Laser-induced transient current technique (L-TCT) at pulsed DC bias or Time-correlated single photon counting (TCSPC). We compared crystallographic and the transport properties of grown crystals depending on the change in the mole ratio of the starting materials, the change in the purity of the starting materials, different degrees of overheating, and different dropping speed of growth ampoule. In case of 1:1 stoichiometric ratio, 40 K overheating and dropping speed of 0.5 mm h -1 , we have grown CsPbBr 3 crystal with resistivity ρ=2.7•10 9 Ωcm evaluated from pulsed I-V characteristics. Pulse-biased L-TCT current waveforms show shorter hole lifetime at the center of the wafer than close in its border. The TCSPC signal indicates non single exponential decay with average rapid component of 0.5 ns.

Laser-induced transient currents were measured after applying pulsed or direct-current bias to a CdZnTe quasi-hemispherical radiation detector with gold contacts. The temporal evolution of current transients was analyzed to evaluate the dynamics of the space charge formation and its spatial distribution. The observed effects were explained by a model involving hole injection from positively biased contacts. Experimental results were complemented by numerical simulations, which supported the model. This paper discusses how the detected phenomena affect the detector performance and proposes an improved detector design.

Investigation of photocurrent relaxations in MAPbBr 3 reveals an unusual increase of current after the bias polarity switch. Observed transient effect show bias dependence similar to that of hole waveforms measured by the laser-induced transient current technique. The combination of these results points to a barrier-induced accumulation of holes beneath the cathode. Accumulated holes relax with a characteristic time 1ms, regardless of contact material.

The transport properties of Large-Volume CZT Bar Detectors in using different material producers are compared in this paper. These gamma-ray detectors can achieve excellent energy resolution approaching the statistical limit provided that high-quality crystals with a low content of defects are used. To reduce the high cost of large-volume high quality CZT material, arrays of small cross section (~ 5x5 mm 2 ) were introduced in the form of 15 to 30 mm long bar detectors with high aspect ratio. The geometry of such bars is convenient to assemble them into a matrix arranged as virtual Frisch-grid detectors. An important task in any CZT detector design is how to minimize the effect of carrier trapping. Investigation and improvement of the transport properties represent a significant contribution to the optimization of the detection performance. We tested two crystals grown by high-pressure Bridgman (A bar- 6×6×19.5 mm 3 ) and traveling heater method (B bar - 6×6×19.3 mm 3 ) with Au/Au semi-transparent electrical contacts. Both CZT materials were obtained from an older production of the manufacturers. We characterized the transport properties by Laser-Induced Transient Currents (L-TCT). A continuous DC electric field up to 1 kV/cm was applied to record a bias-dependent set of electron current waveforms (CWF) for the cathode illumination of both detectors. The corresponding electric field profile is also shown. Significant polarization was found in both detectors. Bias pulsing was applied to suppress space charge formation and to measure the space charge dynamics. Depolarized CWFs up to 600 V were measured for both detectors in this setup. This approach allows us precise evaluation of mobility and lifetime of charge carriers.

In this work, we studied the free-carrier transport properties and space-charge formation/polarization in a CdZnTe bar-shaped radiation detector using the Laser-Induced Transient Current technique. We found out that a steady-state space charge ranging from 8 × 108 to 2.1 × 109 cm−3 is formed throughout the detector at about 0.5 s following biasing. The measured current waveforms were modeled by Monte Carlo simulations after taking into account the electric and weighting fields inside the detector and shielding box. Modeling of the unpolarized waveforms revealed an exceptionally high electron mobility-lifetime product μeτe≥0.095cm2V−1. The observed formation of positive space charge in the biased detector and linear scaling of the current waveform shapes on applied bias revealed that the detector polarization is attributed to carrier injection at the anode. Measurements in pulsed and DC bias in modified electrode geometry proved the surface-charge formation.

Emerging metal-halide perovskites (MHPs) have shown advanced charge transport properties suitable for application in solar cells, photodetectors, and many more. While the past decade witnessed tremendous progress in MHPs, very little is known about the origin of defects and their effect on carrier lifetime. In this study, we compare hybrid and all-inorganic MHPs prepared by inverse temperature solution and high-temperature melt growth to explore the influence of material preparation on the formation of defects. The presence of a low concentration of vacancies was shown in all MHPs regardless of their synthesis method demonstrated by the interaction of positron particles with vacancies and lattices of MHPs and explained by ab initio simulation of positron annihilation. We combined the Raman, Fourier transform infrared (FTIR), and positron annihilation spectroscopy methods to establish the nature of imperfections in MHPs grown using different methods. Our Raman and FTIR results reveal that only the solution-grown crystals are prone to the incorporation of a solvent in bulk during synthesis. In vast majority of studies, the charge carrier lifetime is explored using photoluminescence (PL) spectroscopy as it is a readily available method. However, PL is very sensitive to both bulk and surface recombination phenomena. Combining current waveform time-of-flight and time-resolved photoluminescence spectroscopy methods, the bulk recombination differs by a factor of 2 from crystals grown by solution versus high-temperature melt. The results propose that solvent trapping matters, not intrinsic defects. The study also suggests potential pathways for further improvement of hybrid and all-inorganic MHPs.

We investigated the effect of metallization and spatial homogeneity on the charge collection of sensors prepared from high purity semi-insulating 4H-SiC bulk wafer. We used Au, Ni, Cr or graphene electrical contacts subsequently prepared on the same chip. We also tested sensors prepared from different positions on the wafer. Laser-induced transient current technique (L-TCT) and alpha spectroscopy were used to characterize the charge transport in the sensors. It was found that different sensors polarize at DC bias in the time interval of 0.2–270 s. We observed significant deviation of current transients measured on the sensor with a graphene contact from the sensors with metal contacts, which is attributed to the surface plasmon formed on the graphene-SiC interface. We demonstrated that the sensor polarization is independent of the metallization, whereas it strongly depends on the location on the wafer from which the sensor was cut. This testifies to a significant spatial inhomogeneity of the wafer. We also tested the electrical current relaxation after step-DC biasing as a simple method for the characterization of the sensor polarization. We found that the relaxation profile has extremes in the similar positions as the L-TCT profiles of collected charge. We also showed that using pulse biased L-TCT we are able to choose suitable sensors with slow polarization and to design optimal pulsing conditions including necessary depolarization times for the alpha spectroscopy measurement and L-TCT techniques to achieve long-term stable charge collection. In case of 241Am alpha spectroscopy charge collection efficiency 5–24 % was observed. We framed up model depicting all observed phenomena assuming the space charge formation induced by a blocking cathode in an n-type material and related lifetime reduction. We evaluated the space charge formed in the sensors after 104 s biasing, which ranged from 1.7 × 1014 cm−3 to 7 × 1014 cm−3 in respective sensors.

We investigated the carrier transport and space charge formation in the high purity semi-insulating 4H-SiC bulk single crystal. Using the Laser-induced Transient Current Technique we observed anomalous short current waveform oscillations that are caused by very short carrier lifetime <= 1 ns. We conclude from a detailed inspection of current waveform shape completed by the analysis of collected charge that the electron mobility decreases in an increasing electric field. The saturation value of electron drift velocity 8.7 x 106 cm(2)s(-1) was evaluated. The Hall effect measurement revealed the n-type electrical conductivity and dominant donor energy of E-D = 0.85 eV. We also observed the blocking character of prepared Au contacts, which induce the electron depletion and positive space charge formation in biased sample. The continuous increase of the space charge in a wide time interval of 10(-1) s-10(4) s, attested to testified on a presence of a dispersed impurity band localized below the Fermi energy. Based on these findings, we proposed a theoretical model describing the observed phenomena very well. (C) 2022 Elsevier B.V. All rights reserved.

We measured spectral-resolved photocurrent in a wide range of photon energies from 0.68eV to 4.10eV, current-voltage characteristics, and mid to near-infrared transmittance spectra on a semi-insulating 4H-SiC wafer at room temperature. We identified four deep levels, their energies, and localization radii. The model considers the defects' wavefunction as a linear combination of s- and p-states. Such a linear combination leads to the mixture of dipole allowed and forbidden transitions. The forbidden transitions contribute to a broad photocurrent spectrum, and the allowed transitions appear as sharp photocurrent peaks. The width of photocurrent peaks is related to the localization radius of deep levels. (C) 2021 Elsevier B.V. All rights reserved.

The performance of the CdTe radiation detectors heavily relies on the method of contact preparation. A convenient research method addressing this problem is the laser-induced transient current technique. In this paper, we compare the performance of two CdTe crystals which underwent different metallization processes. We showed that appropriately designed Au/Al contacts induce much less bulk polarization than commercial Pt/In electrodes under the same working conditions and can thus provide a convenient alternative to the industry standard. The comparison was based on the monitoring of the time-dependent sensor polarization measuring transient currents excited by above-bandgap laser illumination complemented by the Am 241 gamma spectroscopy. The theoretical analysis of current waveforms and radiation spectra enabled us to determine the charge carrier mobility, mobility-lifetime products of electrons and holes, and temporal and bias dependence of the space charge formation.