Newly fabricated semiconductor Bi₂O₂Se films exhibit excellent electron transport and optical properties, with potential application in optoelectronics. In this work, using first-principle calculations combined with the modified Becke-Johnson exchange potential, we have systematically investigated the electronic, transport, and optical properties of bulk Bi₂O₂Se. Our calculations have shown that external strain can effectively tune the bulk Bi₂O₂Se electronic bandgap and optical response and that, in particular, the appropriate strain can lead to a transition from an indirect to a direct bandgap. In addition, we found that electron mobility increased with Bi₂O₂Se crystal thickness and that the computed bulk Bi₂O₂Se acoustic-phonon-limited electron mobility could reach ∼940 and 535 cm² V⁻¹ s⁻¹ in the a(b) and c directions at 300 K—which was much higher than that (∼50 cm² V⁻¹ s⁻¹) achieved by the monolayer. There was a clear anisotropy of the electron mobility in bulk Bi₂O₂Se, which could be attributed to the synergistic effect between the elastic modulus anisotropy and the deformation potential. Our results not only have given new insight into the high carrier mobility of different thickness Bi₂O₂Se films (monolayer to bulk) but have also revealed the importance of the electron-transport direction to device performance. Together with the high carrier mobility, strain-tunable electronic structure, and optical response, Bi₂O₂Se films with different thicknesses have been shown to be very attractive for application to optoelectronic and electronic devices.

Pure disulfide ${\mathrm{Cu}\mathrm{In}\mathrm{S}}_2$ ($\mathrm{CIS}$) with a proper band gap (∼1.53 eV) is a promising photovoltaic material, yet it exhibits a relatively low power-conversion efficiency among the $\mathrm{Cu}$-III-${\mathrm{VI}}_2$ (III = $\mathrm{In}$, $\mathrm{Ga}$; VI = $\mathrm{S}$, $\mathrm{Se}$) chalcopyrite solar cells. First-principles calculations show that the inferior photovoltaic performance of $\mathrm{CIS}$ solar cells can be attributed to several factors, including a strong compensation effect, great band-tail states, and defect levels within the band gap, which result in a limited carrier concentration and severe nonradiative recombination of carriers. The strong compensation effect between the ${\mathrm{In}}_{\mathrm{Cu}}$ donor and ${\mathrm{Cu}}_{\mathrm{In}}$ or V${}_{\mathrm{Cu}}$ acceptor defects makes it difficult to maintain a desired p-type conductivity as the elemental chemical potential changes. Besides, ${\mathrm{In}}_{\mathrm{Cu}}$- and ${\mathrm{Cu}}_{\mathrm{In}}$-related defects induce a downward shift of the conduction-band minimum and an upward shift of the valence-band maximum, respectively. The presence of the ${\mathrm{Cu}}_{\mathrm{In}}$-defect level within the band gap is inevitable under the $\mathrm{In}$-poor and $\mathrm{S}$-rich conditions required for the p-type characteristic of $\mathrm{CIS}$. To address these issues, we find that phosphorus ($\mathrm{P}$) incorporation, forming an isoelectronic $2{\mathrm{P}}_{\mathrm{S}}+{\mathrm{In}}_{\mathrm{Cu}}$ defect complex, can enhance the p-type characteristic by consuming the residual electrons of ${\mathrm{In}}_{\mathrm{Cu}}$-donor defects and alleviate their band-tail states by introducing substantial atomic orbital coupling of ${\mathrm{P}}_{\mathrm{S}}$ and ${\mathrm{In}}_{\mathrm{Cu}}$ defects. Moreover, the required $\mathrm{In}$-rich, $\mathrm{S}$-poor, and $\mathrm{P}$-rich conditions, to facilitate the formation of the beneficial $2{\mathrm{P}}_{\mathrm{S}}+{\mathrm{In}}_{\mathrm{Cu}}$ defect complex, can also suppress the formation of ${\mathrm{Cu}}_{\mathrm{In}}$ defects, accordingly, reducing the associated band-tail state and defect state. This study reveals the origins of the stagnated efficiency of $\mathrm{CIS}$ and that defect-complex engineering by anion doping is a feasible way to improve the electronic properties of multicomponent semiconductors.

Nanothermites play an important roles in both civil and military fields. In this paper, using molecular dynamics simulations with reactive force field (ReaxFF), we study the thermally induced reactions of core–shell Al@SiO ₂ nanoparticles to elucidate the underlying reaction mechanism between Al and a metallic oxide. Core–shell Al@SiO ₂ nanoparticles undergo a four-stage explosive reaction after being heated to the ignition temperature. They are, in sequence: (i) Heat is released from the core–shell interface to Al core, and Al core begins to melt. (ii) The melted Al core accelerates the redox exothermic reaction, producing a pure Si shell. (iii) The Si shell moves towards the center of the system under electric field induction, and the distorted Al _n O (n = 4, 5) clusters are ejected from the system’s surface. (iv) The detonation of the nanoparticles, and the formation of final products. Notably, the electric-field-induced Al atoms diffuse faster than the O atoms throughout the reaction. Our findings provide a reference guide for the reactions of nanothermites.

A high-indium-content InGaN quantum-well structure was grown on a strain-relaxed InGaN template to reduce structural strain induced by lattice mismatch. The results show that the InGaN template, following a nanosculpting process, can maintain the good crystal quality of the underlying GaN layer and provide a new lattice parameter for pseudomorphically growing a high-indium-content quantum-well structure, and the fourth-order satellite peak of the multi-quantum-well structure is clearly distinguishable. Atom misalignment, a strain gradient, and a composition undulation along the growth direction in the quantum-well structure were not observed by high-resolution transmission electron microscopy and selected area diffraction.