Interfacial interactions and enhanced optoelectronic properties of GaN/perovskite heterostructures: insight from first-principles calculations

Effects of oxidation on the electronic and optical properties of GaN(0001) surface: First principles study

In order to reveal the influence of n-type doping and point defects on the electronic and optical properties of GaN (0001) surface, the pristine and defective n-GaN (0001) surface models are established. The formation energy, work function, atomic structure, electronic and optical properties of these surfaces are discussed by first-principles calculations. The results show that the defects have the strong tendency to be close to the surface position, and the N interstitial defect (Ni) and the Ga vacancy (VGa) are easily formed. The work function of the surface with VGa drops the greatest, and the conductivity of n-type increases. In addition, the absorption coefficient of the surface with various defects is smaller than that of the pristine n-type surface. The appropriate amount of Ga vacancies can increase the probability of electron emission, but it is not conducive to the absorption of photons.

First-principles calculations of magnetic, electronic and optical properties of binary GaN and ternary CrGaN, CuGaN

Understanding the optical and bonding properties of hybrid metal-halide (C5H16NP) PbX4 (X = Cl, Br, I) perovskite: A density-functional theory study

Investigation on buried interfacial charge carrier dynamics of the MAPbI3/NiO interface by mismatch strain and termination

Coupling between magnetic and optical properties of GaN:TM (TM: V, Cr, Mn, Fe, Co, Ni): First-principle study with LDA-SIC approximation

The structural, electronic, and optical properties of an amorphous SiO2 (a-SiO2) model is investigated by using first-principles calculation. Most research works used beta-cristobalite glass structure as a reference to amorphous silica structure. However, only the electronic properties were been presented without any link towards the optical properties. Here, we demonstrate simultaneous electronic and optical properties, which closely matched to a-SiO2 properties by generating small sample of amorphous quartz glass. Using the Rietveld refinement, amorphous silica structure was generated and optimized using density functional theory in CASTEP computer code. A thorough analysis of the amorphous quartz structure obtained from different thermal treatment was carried out. The structure of amorphous silica was validated with previous theoretical and experimental works. It is shown that small sample of amorphous silica have similar structural, electronic and optical properties with a larger sample. The calculated optical and electronic properties from the a-SiO2 glass match closely to previous theoretical and experimental data from others. The a-SiO2 band gap of 5.853 eV is found to be smaller than the experimental value of ~9 eV. This is due to the underestimation and assumption made in DFT. However, the band gap value is in good agreement with the other theoretical works. Apart from the absorption edge at around 6.5 eV, the refractive index is 1.5 at 0eV. Therefore, this atomic structure can served as a reference model for future research works on amorphous structures.

The effect of gallium vacancy (VGa) and nitrogen vacancy (VN) defects on the electronic structure and optical properties of GaN using the generalized gradient approximation method within the density functional theory were investigated. The results show that the band gap increases in GaN with vacancy defects. Crystal parameters decrease in GaN with nitrogen vacancy (GaN:VN) and increase in GaN with gallium vacancy (GaN:VGa). The Ga vacancy introduces defect levels at the top of the valence band, and the defect levels are contributed by N2p electron states. In addition, the energy band shifts to lower energy in GaN:VNand moves to higher energy in GaN:VGa. The level splitting is observed in the N2p states of GaN:VNand Ga3d states of GaN:VGa. New peaks appear in lower energy region of imaginary dielectric function in GaN:VNand GaN:VGa. The main peak moves to higher energy slightly and the intensity decreases.

The band structure, the density of states, the surface energy, the work function, and the optical properties of GaN(0001)(22) clean surface are calculated systematically by the first-principles plane-wave ultro-soft pseudopotential method based on the density function theory. It is found that the band structure of GaN(0001) surface changes greatly after relaxation, the surface has metallic conductive properties, and there is obvious surface state near the bottom of conduction band. In the effect of dipole moment, the surface charges shift and Ga-terminated surface is positive polar surface. the surface energy and the work function of GaN (0001) surface are obtained to be 2.1 J.m-2 and 4.2 eV, respectively. The optical properties of GaN (0001) surface and bulk phase GaN are analyzed and compared. It is found that there is big difference between them.

Theoretical study of electronic and optical properties of BN, GaN and BxGa1−xN in zinc blende and wurtzite structures

Two dimensional transition metal dichalcogenides (TMDs) have attracted great attention because of the versatile electronic structures. The electronic and magnetic properties of the nanoribbons are still not fully understood, which are crucial for their applications in nanodevices. In this work, the detailed atomic structural, electronic, and magnetic properties of the one dimensional WS2 nanoribbons have been carefully explored by first-principles calculations. The results suggest that the single layer WS2 will first transform into direct band gap semiconductor from indirect band gap of bulk one. Interestingly, the properties of WS2 nanoribbons are greatly affected by the type of the edges: Armchair nanoribbons (ANRs) remain nonmagnetic and semiconducting as that of bulk, whereas zigzag nanoribbons (ZNRs) exhibit ferromagnetic and metallic. Further, the electronic properties can be tuned by applying the external strains to WS2 nanoribbons: Band gap of ANRs experiences a direct-indirect-direct transition and the magnetic moment of ZNRs can be easily tuned by the different strains. All these findings suggest that the TMDs nanoribbons may exhibit extraordinary electronic and magnetic properties, and more importantly, such fascinating characters can be precisely modulated by controlling the edge types and applied strains.

Reduced-Dimensional α-CsPbX3 Perovskites for Efficient and Stable Photovoltaics

Recently, a new type of quasi-1D graphene-like nanoribbons, periodically embedded with four- and eight- membered rings, has been successfully fabricated, and based on this structure, a novel planar 2D carbon allotrope, the so-called the net-Y, has been proposed. Here, we study various nanoribbons derived from such a 2D monolayer focusing on the structure stability, electronic, and transport properties, especially on the physical field coupling effects of electronic behaviors. Very high stability is predicted for various types of nanoribbons by the calculated binding energy and molecular dynamics simulation. Different edge shapes and widths have a significant influence on their electronic properties. Armchair nanoribbons are always semiconductors, and possess a high carrier mobility. After hydrogen termination, some metallic nanoribbons can become semiconductors or quasi-metals with massless Dirac-fermion behavior. In particular, the electronic properties of ribbons can be effectively modulated by applying strain and electric field. The band gap size and the transition from indirect to direct band gap can be realized upon strain or electric field. These flexibly tunable electronic properties for nanoribbons expand their applications in nanoelectronics and optoelectronics.

First-principles study on structural stability and electronic properties of GaAs nanowire undergoing surface oxidization

Incoherent interfaces with large mismatches usually exhibit very weak interfacial interactions so that they rarely generate intriguing interfacial properties. Here we demonstrate unexpected strong interfacial interactions at the incoherent AlN/Al2O3 (0001) interface with a large mismatch by combining transmission electron microscopy, first-principles calculations, and cathodoluminescence spectroscopy. It is revealed that strong interfacial interactions have significantly tailored the interfacial atomic structure and electronic properties. Misfit dislocation networks and stacking faults are formed at this interface, which is rarely observed at other incoherent interfaces. The band gap of the interface reduces significantly to ~ 3.9 eV due to the competition between the elongated Al-N and Al-O bonds across the interface. Thus this incoherent interface can generate a very strong interfacial ultraviolet light emission. Our findings suggest that incoherent interfaces can exhibit strong interfacial interactions and unique interfacial properties, thereby opening an avenue for the development of related heterojunction materials and devices.