Physics of intrinsic point defects in bismuth oxychalcogenides: A first-principles investigation

Abstract

As quasi two-dimensional semiconductors, bismuth oxychalcogenides (BOXs) have been demonstrated as potential candidates for high-speed and low-power electronics because of their exceptional environmental stability and high carrier mobility. Here, thermodynamics of growth and a series of intrinsic defects in BOXs are studied using first-principles calculations. Comparing the chemical potential phase diagrams of BOXs, we find that it is easier to grow Bi2O2Se than to grow Bi2O2S or Bi2O2Te. It is most difficult to grow stable Bi2O2Te because of the existence of various binary phases. Under Se-poor conditions, the intrinsic point defects of Bi replacing Se (BiSe) and Se vacancy (VSe) can form easily and behave as donors because of low formation energy, which is the reason for the n-type character of as-grown Bi2O2Se in experiments. For Bi2O2S, the donor point defect of Bi substituting S (BiS) is also dominant, leading to an n-type carrier. This study of thermodynamics and the physics of intrinsic point defects provides a valuable understanding of BOXs.

Surface electronic structure of bismuth oxychalcogenides

“…The mBJ exchange potential and HSE06 hybrid functional make the gap positive, whereas they retain relative positions of the gap edge extrema: The VBM is situated at the R point, and CBM lies at the M point, resulting in an indirect R-M gap of 150 and 156 meV in mBJ and HSE06 calculations, respectively. In the mBJ (HSE06) spectrum the CB minimum at lies 125 (36) [79] have given the CBM at the point and an indirect gap of 340 meV that is very close to our DFT-1/2 value.…”

High Mobility and Quantum Oscillations in Semiconducting Bi2O2Te Nanosheets Grown by Chemical Vapor Deposition

“…Recent theoretical work on thermodynamics of growth in Bi 2 O 2 X family clearly pointed out that it is most difficult to synthesize stable Bi 2 O 2 Te because of the existence of various binary phases and the narrow window of chemical potential. 31 In a word, the preparation of 2D Bi 2n+ layers that stack alternatively along the c-axis. It is worth noting that this kind of non-neutral layered structure may bring intriguing physical properties but also results in larger interlayer bonding strength and higher surface energy compared to typical neutral-layered materials (such as MoS 2 ), thereby increasing the difficulties to some extent for the growth of ultrathin films on a substrate.…”

“…Subsequently, we tried to synthesize the ultrathin films of layered Bi 2 O 2 Te by a CVD method on mica substrate, whose atomically flat surface and non-neutral layered feature are beneficial to lower the surface potential of 2D Bi 2 O 2 Te during CVD growth. As pointed out by the previous theoretical calculations, 26,31 the formation of stable Bi 2 O 2 Te is quite challenging for its narrow window of chemical potential and the existence of vairous binary phases. Here, two simple substances of Te and Bi 2 O 3 were chosen as evaporation sources (Figure 1c), which were separatedly located at two To verify the crystal structure and chemical compositions of as-synthesized 2D Bi 2 O 2 Te crystals, transmission electron microscope (TEM) imaging along two zone axes (namely [001] and [010]) were conducted.…”

PbSe Quantum Dots Sensitized High-Mobility Bi2O2Se Nanosheets for High-Performance and Broadband Photodetection Beyond 2 μm

“…It is noted that the as-prepared Bi 2 O 2 Se was slightly Se deficient with a Bi:O:Se ratio of 2:2.1:0.9, as indicated by the energy dispersive X-ray spectra shown in Supporting Information Figure S1a. The Se vacancy was believed to contribute to the heavily n-type doped behavior of Bi 2 O 2 Se, which could be compensated by using Se as the direct sublimation vapor source . The as-fabricated Bi 2 O 2 Se was then transferred to SiO 2 /Si substrate by using HF etching and a poly­(methyl methacrylate) (PMMA)-assisted handling processes for further device fabrication.…”