Numerical characterization of thermal and optical properties of monolayer GaN nanostructures doped with group IV materials

Abstract

Bulk GaN has been one of the prominent materials for a long time in employment of laser, LED and transistors. Due to its superior electrical characteristics, its low-dimensional hexagonal counterpart is becoming popular. To facilitate the uprising scope of this hon- eycomb shape, this study has focused on structural, thermal, electronic and optical proper- ties of zigzag GaN nanostructures considering the presence of impurity atoms. The room temperature thermal conductivity of zigzag GaN nanoribbon (ZGaNNR) has been found to be ∼ 11 Wm−1 K−1 using the molecular dynamics approach in line with the Green- Kubo method. Four distinct impurity atoms have been inserted in the pristine structure in single, pair, and trio configurations to investigate the impact of doping concentration on thermal conductivity. An improvement in the thermal conductivity is found when carbon and silicon are chosen as dopant atom. On the other hand, an opposite trend is obtained for germanium and tin impurities due to increased rate of phonon scatterings. Later, the size dependence of thermal conductivity is examined by altering the width of the ribbon. The results demonstrate that thinner ribbons have a higher phonon scattering rate, which limits the heat transport. As the temperature of the ribbon rises, phonon movements are sup- pressed due to increased scattering and heat energy is obtained at slower rate. The thermal conductivity is also extremely sensitive to the presence of vacancy defects in the crystal, and it decreases monotonically for all types of defect patterns namely- point, edge and pair vacancy. Our findings suggest that carbon and silicon doped ZGaNNRs are suitable for thermal management in devices whereas germanium and tin impurity incorporation can be beneficial in heat energy extraction effectively. The structural, electronic, and optical char- acteristics of two-dimensional pristine GaN nanostructures along the zigzag direction have been investigated using density-functional theory. Group IV impurities such as carbon, sil- icon, germanium and tin have been considered as dopant to vary the doping concentration from 2.5% to 5.0%. Perdew-Burke-Ernzerhof (PBE) functionality reveals the fact that the newly formed impurity bonds with Ga and N atoms is strongly influenced by impurity size and doping quantity. Impurities having atomic size closer to the replaced atom gives more stable nanostructures in all cases. All impurity atoms affect the bandgap of doped structure

compared to the pristine, resulting in a degenerate states. Density functional investigation on bandstructure and density of states reveal that the indirect nature of pristine GaN be- comes direct under the effect of chemical doping. Our findings reveal that the stability in the crystal which is obvious from density of states analysis. The complex dielectric func- tion, the absorption coefficient, and the electron energy loss functions are affected by the incorporation of group IV impurities. In both in-plane and out-of-plane polarization, all impurity atoms cause a red shift in the optical spectra. Peak strength is likewise very sus- ceptible to impurity, and it declines as doping concentration rises. Inter-band transitions are also generated by the degenerate circumstances, resulting in some noticeable peaks in the lower energy range. It is evident that group IV doped GaN nanostructures are poten- tially appropriate in different optoelectronic, photocatalyst, visible, IR and UV ray detector devices.