Understanding the type, formation energy and capture cross section of defects is one of the challenges in the field of organometallic halide perovskite (OMHP) devices. Currently, such understanding is limited, restricting the power conversion efficiencies of OMHPs solar cells from reaching their Shockley-Queisser limit. In more matured semiconductors like Si, the knowledge of defects was one of the major factor in successful technological implementation. This knowledge and its control can make a paradigm in development of OMHP devices. Here, we report on deep level (DL) defects and their effect on free charge transport properties of single crystalline methylammonium lead bromide perovskite (MAPbBr3). In order to determine DL activation energy and capture cross section we used photo-Hall effect spectroscopy (PHES) with enhanced illumination in both steady-state and dynamic regimes. This method has shown to be convenient due to the direct DL visualization by sub-bandgap photo-excitation of trapped carriers. DLs with activation energies of EV + 1.05 eV, EV + 1.5 eV, and EV + 1.9 eV (or EC -1.9 eV) were detected. The hole capture cross section of h = 4 × 10 -17 cm 2 is found using photoconductivity relaxation after sub-bandgap photo-excitation. Here, we found the DL defects responsible for non-radiative recombination and its impact on band alignment for the first time. Additionally, the transport properties of single crystal MAPbBr3 is measured by Time of Flight

A method is presented for the determination of the carrier drift mobility, lifetime, electric field distribution, and the dynamics of space charge formation, including the detrapping energy and capture cross-section of the dominant trap level in polarizing semiconductor radiation detectors. The procedure stems from the laser-induced transient current measurements done at a steady-state and pulsed biasing and at variable temperature. The approach allows us the direct determination of detector parameters from measured data without a complex mathematical treatment. The detrimental effect of surface carrier recombination often hampering the evaluation of detector properties is eliminated. Lifetime worsening caused by the space charge formation is included. The usefulness of the procedure is demonstrated on a CdTe radiation detector.

No abstract

Photo-Hall effect spectroscopy was used in the study of deep levels in high resistive CdZnTe. The monochromator excitation in the photon energy range 0.65-1.77 eV was complemented by a laser diode high-intensity excitation at selected photon energies. A single sample characterized by multiple unusual features like negative differential photoconductivity and anomalous depression of electron mobility was chosen for the detailed study involving measurements at both the steady and dynamic regimes. We revealed that the Hall mobility and photoconductivity can be both enhanced and suppressed by an additional illumination at certain photon energies. The anomalous mobility decrease was explained by an excitation of the inhomogeneously distributed deep level at the energy E v +1.0 eV enhancing thus potential non-uniformities. The appearance of negative differential photoconductivity was interpreted by an intensified electron occupancy of that level by a direct valence band-to-level excitation. Modified Shockley-Read-Hall theory was used for fitting experimental results by a model comprising five deep levels. Properties of the deep levels and their impact on the device performance were deduced.

We combined steady-state photoconductivity and laser-induced transient current measurements under above-band-gap illumination to study the space charge formation in CdZnTe. Analytical as well as numerical models describing space charge limited photocurrents were developed and an excellent agreement with measured data was obtained especially with the Drift-diffusion model. Linear rise of photocurrent at low bias was observed and ascribed to the trapping of injected holes at the region close to the cathode side. Influence of space charge formation, photoconductive gain, contribution of shallow and deep levels to photocurrent-voltage characteristics were numerically simulated. According to the measurements and calculations, recent principles used at the evaluation of detector properties, mainly the mobility-lifetime product, via the photoconductivity are critically assessed.

This paper describes an application of infrared light-induced de-polarization applied on a polarized CdZnTe detector working under high radiation fluxes. We newly demonstrate the influence of a high flux of X-rays and simultaneous 1200-nm LED illumination on the spectroscopic properties of a CdZnTe detector. CdZnTe detectors operating under high radiation fluxes usually suffer from the polarization effect, which occurs due to a screening of the internal electric field by a positive space charge caused by photogenerated holes trapped at a deep level. Polarization results in the degradation of detector charge collection efficiency. We studied the spectroscopic behavior of CdZnTe under various X-ray fluxes ranging between 5×105 and 8×106 photons per mm2 per second. It was observed that polarization occurs at an X-ray flux higher than 3×106 mm−2·s−1. Using simultaneous illumination of the detector by a de-polarizing LED at 1200 nm, it was possible to recover X-ray spectra originally deformed by the polarization effect.

Abstract. Thin-film hydrogen peroxide vapor sensors made from Co-doped SnO 2 and La-doped ZnO were manufactured using the high-frequency magnetron sputtering method. Thicknesses of deposited doped metal oxide films were measured and their morphology was investigated. The gas sensing characteristics of the prepared sensors were measured at different concentrations of hydrogen peroxide vapors and different operating temperatures of the sensor. It was found that both sensors made from doped metal oxides SnO 2 and ZnO exhibit a sufficient response to 10 ppm of hydrogen peroxide vapors at the 200 and 220 • C operating temperature, respectively. It was established that the dependencies of the response on hydrogen peroxide vapor concentration have a linear character for prepared structures at the 150 • C operating temperature and can be used for determination of hydrogen peroxide vapor concentration.

We studied the growth of the surface oxide layer on four different CdTe and CdZnTe X-ray and gamma-ray detector-grade samples using spectroscopic ellipsometry. We observed gradual oxidization of CdTe and CdZnTe after chemical etching in bromine solutions. From X-ray photoelectron spectroscopy measurements, we found that the oxide consists only of oxygen bound to tellurium. We applied a refined theoretical model of the surface layer to evaluate the spectroscopic ellipsometry measurements. In this way we studied the dynamics and growth rate of the oxide layer within a month after chemical etching of the samples. We observed two phases in the evolution of the oxide layer on all studied samples. A rapid growth was visible within five days after the chemical treatment followed by semi-saturation and a decrease in the growth rate after the first week. After one month all the samples showed an oxide layer about 3 nm thick. The oxide thickness was correlated with leakage current degradation with time after surface preparation.