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 OMHP solar cells from reaching their Shockley–Queisser limit. In more mature semiconductors like Si, the knowledge of defects is one of the major factors in successful technological implementation. This knowledge and its control can make a paradigm shift in the development of OMHP devices. Here, we report on deep level (DL) defects and their effect on the free charge transport properties of the single crystalline methylammonium lead bromide (MAPbBr₃) perovskite. 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 E_V + 1.05 eV, E_V + 1.5 eV, and E_V + 1.9 eV (or E_C − 1.9 eV) were detected. The hole capture cross section of σ_h = 4 × 10⁻¹⁷ cm² is found using photoconductivity relaxation after sub-bandgap photo-excitation. Here, our experimental results demonstrate the existence of DL defects responsible for non-radiative recombination and their positions inside the bandgap for the first time. Additionally, the transport properties of single crystal MAPbBr₃ are investigated by Time of Flight (ToF) measurements at several biases. These measurements further confirm the increase of Hall mobility and the enhancement of hole transport produced by sub-bandgap illumination in MAPbBr₃ devices. The analysis of charge carrier transport by ToF measurements in combination with the energy of DLs identified by PHES can explain the long hole carrier lifetime in MAPbBr₃ devices, while the electron carrier lifetime is largely affected by trap-assisted recombination. Here, our studies provide strong evidence for deep levels in OMHPs and open a richer picture of the role and properties of deep levels in MAPbBr₃ single crystals as a system model for the first time. The deeper knowledge of the electronic structure of OMHPs could open further opportunities in the development of more feasible technologies. Indeed, knowledge of the exact positions of DLs is beneficial in controlling these defects by crystal growth modification to eliminate these defects as was done for classical inorganic semiconductors, for example, in Si, GaAs, and CdTe development.

The energy dependence of the electronic scattering time is probed by Landau level spectroscopy in quasineutral multilayer epitaxial graphene. From the broadening of overlapping Landau levels we find that the scattering rate $1/\tau$ increases linearly with energy $ϵ$. This implies a surprising property of the Landau level spectrum in graphene—the number of resolved Landau levels remains constant with the applied magnetic field. Insights are given about possible scattering mechanisms and carrier mobilities in the graphene system investigated.

Real-time Pockels imaging is performed on semi-insulating CdZnTe to measure the electric field profile in the material bulk. In steady-state room temperature conditions the measured electric field profile is uniform, consistent with a low space charge concentration. At temperatures $<270\text{K}$ a significant nonuniform electric field profile is observed, which we explain in terms of temperature-induced band bending at the metal-semiconductor interface, causing the formation of positive space charge in the bulk. Similar electric field distortion effects are observed when room temperature CdZnTe is irradiated by x-rays, causing a high rate of photoinduced charge injection.

Transient-current technique was used for measuring the profile of the electric field in CdTe and CdZnTe samples excited by an ²⁴¹ Am α-particle source. Current waveforms were analyzed by a general model, which involved both the effect of the space charge in the depleted region and charge trapping. The carrier mobility and the electric-field profile were also evaluated in this way. The maximum electric field was observed close to the cathode, whereas the minimum occurred near the anode. The decrease in the strength of the electric field from cathode to anode was explained in terms of a positive space charge formed in the detector's volume. Measurements under incomplete depletion, when an “inactive” region with zero electric field was observed under the anode, were reported as well. Space-charge densities of 10 ¹¹ -10 ¹² cm ^-3 in CdTe and 10 ¹⁰ cm ^-3 in CdZnTe were evaluated. The dynamics of electron-hole plasma formed by a single α-particle absorption event was analyzed in detail and used as a complementary test of our reported model. An excellent agreement with theory was obtained.