Advances in Condensed Matter Physics

The manuscript substantiates the structural and electronic properties of covalent triazine frameworks (CTF)/As van der Waals heterostructures (vdWh) employing the standard first-principles calculation method. The numerical results designate that the CTF/As vdWh has robust crystal structures, a type-II band alignment (BA), and an indirect bandgap of 1.44 eV. The calculated results demonstrate that the strain could lead to interesting indirect-direct semiconductor transitions, while the external electric field could give rise to type-II to type-I BA and semiconductor-metal transitions. The underlined outcomes present the workability of CTF/As vdWhs in unprecedented high-performance optoelectronic equipment.

In this study, the structural, electronic, elastic, phonon vibration, thermodynamic features, and optical properties of the orthorhombic phase of (space group Pnma) were examined by first-principles calculations utilizing the plane wave ultrasoft pseudopotentials in generalized gradient approximations (GGAs) and with Hubbard on-site correction (DFT + U). To improve the value of the band gap, the exchange correlation potential is also approximated with Hubbard correction (GGA + U). The equilibrium state properties such as lattice parameters, unit cell volume, bulk modulus, and its derivative were calculated and are in good agreement with the existing data. The mechanical properties such as bulk modulus, shear modulus, Young’s modulus, and elastic anisotropy were determined from the obtained elastic constants. The ratio of bulk modulus to shear modulus confirms that the orthorhombic phase of is a ductile material. In addition, the longitudinal sound velocity, transverse sound velocity, and Debye temperature for have been computed. The absence of negative frequencies in the phonon dispersion curve and the phonon density of states confirm that in the orthorhombic phase is dynamically stable. The thermodynamic parameters such as free energy, entropy, and heat capacity were examined with variations in temperature. Finally, the absorption coefficient, dielectric constant, energy loss function, reflectivity, and refractive index are discussed in detail in the spectral range 0–1.6 Ry (21.77 eV). The polarizations along (100), (010), and (001) directions significantly show different optical responses.

Ternary boron-carbon-nitride compounds are the hardest, chemically stable, and most applicable semiconductors in optoelectronic devices. We investigate the quasi-particle and excitonic properties of type II o-BC₂N using many-body perturbation theory (MBPT). The state-of-the-art GW and BSE methods were used to determine the accurate band gap and excited-state characteristics of this material. We simulate the convergence test and structural optimization in DFT, which is the starting point for the GW calculation. We also compute the convergence test of the parameters in GW and BSE. As a result, the bandgap of our system is found to be 2.31 eV and 1.95 eV using the GW approximation and DFT-PBE, respectively. Since the valence and conduction band edges are located at different Brillouin zones, we decide that o-BC₂N is an indirect bandgap semiconductor. In addition, by applying the scissor operator, we corrected the quasi-particle bandgap, which shows almost the same result as the GW approximation. Furthermore, using the BSE algorithm, we calculate the optical bandgap of type II o-BC₂N to be 4.0 eV with the excitonic effect and 4.4 eV without the excitonic effect. The highest peaks of the imaginary dielectric function with the excitonic effect shift to a lower energy level at 11 eV than without the excitonic effect at 13.5 eV. The electron charge distribution is computed by fixing the hole position. Finally, we suggest that type II o-BC₂N is promising for the application of optoelectronic semiconductors.

TiO₂ nanoparticles (NPs) were produced via utilized nanosecond laser ablation of titanium in water. The description of these NPs was employed utilizing XRD, SEM, and UV-VIS. Then, optoelectronic properties were investigated via a drop-casting of TiO₂ NPs on the Si wafer substrate. XRD results show the formation of anatase TiO₂. The SEM exhibits a spherical shape with sizing changing from 5 nm to 50 nm. The bandgap was 3.6 eV which was determined from the Tauc chart. The IV characteristic of the TiO₂NPs/Si heterojunction showed good rectifying behaviour, with a maximum responsivity of about 0.7 A/W at 310 nm.

Single and mixed-halide perovskite solar cells have attracted much research attention in recent years due to the conditions of low-cost thin film solar cell technology. For this current research, perovskite materials CH₃NH₃PbCl₃, CH₃NH₃PbI₂Cl, CH₃NH₃PbICl₂, and CH₃NH₃PbI₃ have been synthesized and deposited on clean glass substrates by spin coating process. The structural and morphological properties of the prepared thin films have been studied by X-ray diffraction and Scanning electron microscopy. All the perovskite showed fine crystallinity, possessing a tetragonal phase. The average crystallite sizes of the prepared samples are obtained to be 20.77 nm, 30.18 nm, 31.11 nm, and 42.23 nm, respectively. The lattice strain decreased with increasing crystallite size. A drastic change was observed in the morphological properties of the perovskites. The perovskite grains change from microrods to microcube by substituting iodine with chlorine ions.

Electronic and optical properties of type-II InGaN/GaNSb/GaN quantum-well (QW) structures are investigated by using the multiband effective mass theory for potential applications in red light-emitting diodes. The heavy-hole effective mass around the topmost valence band is not affected much by the insertion of the GaNSb layer, and the optical matrix elements are greatly increased by the inclusion of the GaNSb layer in the InGaN/GaN QW structure. As a result, the type-II InGaN/GaNSb/GaN QW structure shows a much larger emission peak than the conventional type-I QW structure owing to the decrease in spatial separation between electron and hole wavefunctions, in addition to the reduction of the effective well width. It is also observed that the In content in InGaN well can be significantly reduced for the type-II QW structure with a large Sb content, compared to that for the type-I QW structure.