Deep levels in high resistive CdTe and CdZnTe explored by photo-Hall effect and photoluminescence spectroscopy

et al. 2019

Energy Environ. Sci.

Self Cite

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

Section: Deep Level Recombination Parametersmentioning

confidence: 84%

Deep levels, charge transport and mixed conductivity in organometallic halide perovskites

Musiienko

Moravec

et al. 2019

Energy Environ. Sci.

Self Cite

“…For this contribution, a single crystalline CdZnTe with a zinc content of 4.5 % grown by the vertical gradient freeze method at the Institute of Physics, Charles University was chosen. N-type sample with dimensions of 3x2x12 mm 3 prepared by a standard method 13 was used in the classic six-contact Hallbar shape convenient for galvanomagnetic measurements. The sample was distinguished by an unusual decrease of mobility, the appearance of negative differential photoconductivity (NDPC) and several…”

Section: Sample Properties and Photo-hall Effect Measurementsmentioning

confidence: 99%

“…The material quality strongly controls the price of the ingots 7 and further investigation and improvement of the material are therefore needed. The existing thermal emission spectroscopy methods suffer from known limitations when unambiguously identifying DLs properties, especially in case of very deep levels with trapping energy well above the half of the band gap energy 12,13 . In our previous paper 13 we showed that photo-Hall effect spectroscopy (PHES) is a convenient method for the complementary study of deep level properties.…”

Section: Introductionmentioning

confidence: 99%

“…The existing thermal emission spectroscopy methods suffer from known limitations when unambiguously identifying DLs properties, especially in case of very deep levels with trapping energy well above the half of the band gap energy 12,13 . In our previous paper 13 we showed that photo-Hall effect spectroscopy (PHES) is a convenient method for the complementary study of deep level properties. The Hall mobility 𝜇 𝐻 = 𝜎𝑅 𝐻 determined by PHES experiment, where σ, R H are the conductivity and Hall coefficient, respectively, is an excellent parameter that may be used for identification of structural imperfections and inhomogeneity inducing electric potential non-uniformities in the material 14 .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Dual-wavelength photo-Hall effect spectroscopy of deep levels in high resistive CdZnTe with negative differential photoconductivity

Musiienko

Journal of Applied Physics

Moravec

et al. 2017

Self Cite

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.

“…Low hole mobility and enhanced hole trapping reduce the charge collection efficiency (CCE) and produce long asymmetric tail at measured energy spectra (hole tailing). Thus, poor hole mobility-lifetime product (µ h τ h ) and relevant defect structure [7,9] are critical issues in the utilization of (CdZn)Te radiation detectors.…”

Section: Introductionmentioning

confidence: 99%

Charge Sharing in (CdZn)Te Pixel Detector Characterized by Laser-Induced Transient Currents

Vasylchenko

Belas

et al. 2019

Sensors

Self Cite

Performance of the (CdZn)Te pixelated detectors heavily relies on the quality of the underlying material. Modern laser-induced transient current technique addresses this problem as a convenient tool for characterizing the associated charge distribution. In this paper, we investigated the charge sharing phenomenon in (CdZn)Te pixel detector as a function of the charge collected on adjacent pixels. The current transients were generated in the defined 4 mm 2 spots using 660 nm laser illumination. Waveforms measured on the pixel of interest and its surroundings were used to build the maps of the collected charge at different biases. The detailed study of the maps allowed us to distinguish the charge sharing region, the region with a defect, and the finest part in terms of the performance part of the pixelated anode. We observed the principal inhomogeneity complicating the assignment of the illuminated spot to the nearest pixel.Sensors 2020, 20, 85 2 of 14 particular design if wired in a form of a virtual coplanar grid. These detectors are featured by specific electrode configurations that in general provide a particular distribution of electric field inside the sample. According to Shockley-Ramo theorem [13], these field effects induce signal as follows: