Polat Narin

The electronic properties of the hexagonal Boron Phosphide (h-BP) monolayer have been investigated by first-principles calculations. The electronic band structure of the h-BP monolayer has been calculated using GPAW with PBE and GLLB-SC exchange correlations (XCs). The energy band gaps of the h-BP monolayer are found to be 0.89 eV and 1.05 eV for PBE and GLLB-SC, respectively. It is shown that GLLB-SC in calculations as XC ensures a more accurate energy band gap than the PBE. As well as the electronic calculations of the unstrained h-BP monolayer, the strain calculations are performed between +5 and -5 %. The strain in the h-BP monolayer changed the energy band gap between 0.78 eV and 1.24 eV for GLLB-SC and between 0.66 eV and 1 eV for PBE. In this applied strain range the studied structure shows the direct band gap semiconductor behavior.

Metal–organic chemical vapor deposition (MOCVD) is one of the best growth methods for GaN‐based materials as well‐known. GaN‐based materials with very quality are grown the MOCVD, so we used this growth technique to grow InAlN/GaN and AlN/GaN heterostructures in this study. The structural and surface properties of ultrathin barrier AlN/GaN and InAlN/GaN heterostructures are studied by X‐ray diffraction (XRD) and atomic force microscopy (AFM) measurements. Screw, edge, and total dislocation densities for the grown samples have been calculated by using XRD results. The lowest dislocation density is found to be 1.69 × 10 ⁸ cm ⁻² for Sample B with a lattice‐matched In _0.17 Al _0.83 N barrier. The crystal quality of the studied samples is determined using (002) symmetric and (102) asymmetric diffractions of the GaN material. In terms of the surface roughness, although reference sample has a lower value as 0.27 nm of root mean square values (RMS), Sample A with 4‐nm AlN barrier layer exhibits the highest rough surface as 1.52 nm of RMS. The structural quality of the studied samples is significantly affected by the barrier layer thickness. The obtained structural properties of the samples are very important for potential applications like high‐electron mobility transistors (HEMTs).

This study focuses on the growth and physical properties of ZnO thin films on different substrates grown by mist-CVD enhanced with ozone (O₃) gas produced by corona discharge plasma using O₂. Here, O₃ is used to eliminate the defects related to oxygen in ZnO thin films. ZnO thin films are grown on amorphous soda-lime glass (SLG) and single crystals SiO₂/Si (100) and c-plane Al₂O₃ substrates at 350°C of low growth temperature. All ZnO thin films show dominant (0002) diffraction peaks from X-ray diffraction (XRD). As expected, full width at half maximum (FWHM) of (0002) is decreasing in ZnO thin films on single-crystal substrates, especially c-Al₂O₃ due to similar crystal structure. It is found that the strain in the films is lowest in ZnO/c-Al₂O₃. The surface morphologies of the thin films are studied with atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements. Grown ZnO films have a hexagonal and triangular nanostructure with different nanostructure sizes depending on the used substrate types. The calculated surface roughness is dramatically decreased in ZnO/c-Al₂O₃ compared to the other grown structures. The confocal Raman measurements show the E₂(H) peak of ZnO thin films at 437cm⁻¹. It is suggested that O₃ gas produced by corona discharge plasma using O₂ can be useful to obtain better crystal quality and physical properties in ZnO thin films.

In this study, the electronic and optical properties of wurtzite Mg_xZn_1−xO structures for different Mg mole fractions (x) are studied using Density Functional Theory (DFT). In calculations, the generalised gradient approximation (GGA + U) formalism is used with the Hubbard parameters (U) are applied to Zn-3d and O-2p electrons of ZnO. The calculated electronic band structures show that the band gap energies of the investigated structures increase linearly with increasing Mg mole fraction from 0 to 31.25% which is also quantitatively consistent with the previous experimental results. In addition, the electron effective masses of investigated Mg_xZn_1−xO structures are calculated. The electron effective masses of investigated structures show an increment linearly with increasing Mg mole fractions. The optical results show that the absorption edges of the structures move toward the higher energies region as the Mg mole fractions increase.