No abstract

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

No abstract

Symmetrical, non-linear and current-voltage (I -V ) characteristics of a metal-semiconductormetal (M-S-M) structure of two metallic Schottky contacts fabricated to a p-type semiconductor were modeled by treating the semiconductor as a resistor sandwiched between two identical head-to-head Schottky barriers. The voltage distributions along the M-S-M structure were numerically determined and found that the voltage drop across the reverse-biased Schottky barrier is dominating at the low bias voltage, and the dominant range depends on the value of the resistor of the semiconductor bulk. The field dependence of barrier height due to the image force was proposed to be the mechanism for the current through the M-S-M structure when the voltage drop across the reverse-biased barrier is dominating. The proposed model was applied to the I -V curves measured at different temperatures on low-resistivity p-type CdTe with Au contacts and the density of the effective acceptors calculated, and the zero-field Schottky barrier height and the Richardson constant were extracted using the activation energy method. The extracted parameters fitted well with that published for the same material structure.

The interaction of free carriers with defects and some critical defect properties are still unclear in methylammonium lead halide perovskites (MHPs). Here, a multi-method approach is used to quantify and characterize defects in single crystal MAPbI 3 , giving a cross-checked overview of their properties. Time of flight current waveform spectroscopy reveals the interaction of carriers with five shallow and deep defects. Photo-Hall and thermoelectric effect spectroscopy assess the defect density, cross-section, and relative (to the valence band) energy. The detailed reconstruction of free carrier relaxation through Monte Carlo simulation allows for quantifying the lifetime, mobility, and diffusion length of holes and electrons separately. Here, it is demonstrated that the dominant part of defects releases free carriers after trapping; this happens without non-radiative recombination with consequent positive effects on the photoconversion and charge transport properties. On the other hand, shallow traps decrease drift mobility sensibly. The results are the key for the optimization of the charge transport properties and defects in MHP and contribute to the research aiming to improve perovskite stability. This study paves the way for doping and defect control, enhancing the scalability of perovskite devices with large diffusion lengths and lifetimes.

We explored the growth and characteristics of CdTe doped with Sn to heighten our understanding of the role of deep levels on electrical compensation and trapping. We demonstrated, for the first time, the strong dependence of the Sn Cd charge state on the Fermi-level variation (2-3kT) in high-resistivity CdTe. The concentration of deep traps for electrons was determined by the number of doubly positively charged Sn 2+ atoms. Thermoelectric-effect spectroscopy and photovoltage measurements revealed the conversion of the Sn Cd defect from the electron Sn Cd 2+ trap to the hole Sn Cd 0 trap. The results agree well with the existence of a negative U-center in the Sn Cd 0/2+ defect. We also showed that the neutral Sn defect is responsible for the near midgap C-band → bound hole radiative transitions band with a maximum at 0.76 eV.

No abstract