GROWN, CRYSTAL STRUCTURE AND MECHANISM OF PHOTOCONDUCTIVITY OF BiOCl SINGLE CRYSTALS

Abstract.

Purpose. Oxyhalides of bismuth BiOX (X = Cl, Br, I) are very interesting materials which find various applications as X-ray luminescent screens, as anti-Stokes converters, photocatalyst, usual luminophors and as photoconductive analyzer of linear polarized radiation in the 0.24-1.2µ spectral region. The great interest for these materials is strongly related to the influence of dimensionality on the beha viour of physical properties (they are 2D structured materials). Bismuth oxyhalides are one of the V-VI-VII group compound semiconductors belonging to the tetragonal system. Methods. The BiOX single crystals were grown by the chemical gas transport reactions method in the closed volume. The lattice parameters of the crystals were determined by X-ray powder diffraction with a Si internal standard (high purity) spectral dependences of the steady-state photocurrent (photoconductivity) were recorded using a LOMO MDR3 monochromator. Low temperatures were obtained by mounting the sample in an UTREKS continuous flow cryostat. The decay time measurements were performed using pulse UV-laser LGI-21. Results. The best bismuth oxyhalide crystals were obtained at the 8-10 Torr pressure of transport agent. The layered structure BiOX can provide the space large enough to polarize the related atoms and orbitals. The induced dipole can separate the hole-electron pair efficiently, enhancing photocatalytic activities. BiOX has an indirect-transition bandgap so that the excited electron has to travel certain k-space distance to be emitted to valence band. Conclusions. The optimal temperature region on BiOCl crystals based photodetectors is in the range 80-400 K. BiOCl single crystals are stable in air, and their parameters do not depend on the environment, which eliminates the need for sealing. The selectivity of BiOCl spectral characteristics make them good radiation detectors of the nitrogen, argon and helium-cadmium lasers, as well as some of the semiconducting light-emitting diodes (LEDs). Therefore, they can be used in optoelectronic circuits in conjunction with these lasers and LEDs

Keywords: bismuth oxyhalides, layer single crystals, photoconductivity, semiconducting light-emitting diodes (LEDs)

https://doi.org/10.24144/2415-8038.2020.47.55-62