Binbin Zhang

Lead free halide perovskite Cs3Bi2I9 bulk crystals grown by a low temperature solution method

As a member of the bismuth iodide family compounds, Cs3Bi2I9 perovskite shows potential applications in photovoltaic devices and radiation detectors, due to the absence of toxic lead and its high air and moisture stability. In this work, we report Cs3Bi2I9 bulk crystals grown by a low temperature solvent volatilized crystallization method. The morphology of the single crystals exhibits a well symmetric hexagonal shape, with a layered structure along the [00l] direction. Three defect related transitions (iodine substituting bismuth (IBi) to the valence band maximum (VBM), the conduction band minimum (CBM) to caesium substituting bismuth (CsBi1−/2−), and the CBM to caesium substituting iodine (CsI1+/2+)) are identified in 10 K photoluminescence spectra, with dissociation energies of 47.87 meV, 45.28 meV, and 52.01 meV, respectively. The anisotropic resistivities along the [00l] and [l00] directions are compared, with values of 11.08 GΩ cm and 0.77 GΩ cm, respectively, which is attributed to the difference of carrier mobility. This is further certified by the first principles calculations, which demonstrate that the effective masses along the [00l] and [l00] directions are 3.22me (electrons)/2.14me (holes) and 0.327me (electrons)/0.946me (holes), respectively. The Cs3Bi2I9 device exhibits fast photoresponse to optical light, with an on–off ratio of ∼24 along [l00], which is fifteen times higher than that along [00l]. This photoelectric anisotropy dictates the potential applications in photovoltaic devices and radiation detectors.

Preparation of indium tin oxide contact to n-CdZnTe gamma-ray detector

The nonmetal electrode material Indium Tin Oxide (ITO) has advantages of excellent conductivity, higher adhesion, and interface stability, showing potential to replace the metallic contacts for fabrication of CdZnTe (CZT) X/γ-ray detectors. In this work, high quality ITO electrodes for n-type CZT crystals were prepared by magnetron sputtering under a sputtering power of 75 W and a sputtering pressure of 0.6 Pa. A low dark current of ∼1 nA is achieved for the 5 × 5 × 2 mm3 ITO/CZT/ITO planar device under 100 V bias. The characteristics of Schottky contact are presented in the room temperature I-V curves, which are similar to those of the Au contact detectors. Based on the thermoelectric emission theory, the contact barrier and resistance of ITO electrodes are evaluated to be 0.902–0.939 eV and 0.87–3.56 × 108 Ω, respectively, which are consistent with the values of the Au electrodes. The ITO/CZT/ITO structure detector exhibits a superior energy resolution of 6.5% illuminated by the uncollimated 241Am @59.5...

Improvement of the THz response of Zn1−xMnxTe bulk crystals grown by a temperature gradient solution method

As a type of AII1−xMnxBVI alloy, Zn1−xMnxTe ingots with a diameter of 30 mm are grown as large single crystals by a temperature gradient solvent method under Te-rich conditions. The orange-red Zn1−xMnxTe crystals are cut and processed into size-appropriate wafers for fundamental studies, as well as for THz spectroscopy and magnetization response analyses. Mn segregation associated with the growth conditions is identified in the as-grown crystals, and an enriched higher concentration of Mn is observed inside the Te inclusion. To evaluate the effect of Mn on the Zn1−xMnxTe crystal, the site occupation is calculated via an ab initio study, and is further confirmed by electrical and optical property measurements. Mn tends to substitute Zn to form MnZn in Zn1−xMnxTe, which results in a low density of free charge carriers, through which the THz detection sensitivity is enhanced by 15–25% compared to the intrinsic ZnTe. Moreover, evident paramagnetic magnetization behavior is observed at variable temperatures due to the random distribution of an isolated Mn (Mnioct,Te6) spin with S = 5/2. We note that further optimization of the THz performance can be achieved by optimizing the growth process and tailoring the Mn content.