First Principles DFT + U Calculations of the Electronic Properties of ZnO/GaN Heterostructure

ZnO/GaN heterostructures are promising systems for solar cells, light-emitting diodes and photocatalytic applications due to their appropriate band gaps that correspond to the wavelength range of visible light and thus have attracted wide attention over the past ten years. In this study, investigations of structural and electronic properties of bulk ZnO, GaN and ZnO/GaN superlattice have been performed based on first-principles calculations within the density functional theory. For a more accurate description of the electronic properties of bulk semiconductor crystals, Hubbard correction to generalized gradient approximation (GGA + U) was applied. The obtained results show that this calculation method allows to obtain reliable band edge positions, which are the defining parameters in determining the average electrostatic potential of each bulk material. Also, the use of the GGA + U method allows obtaining the lattice mismatch of bulk ZnO and GaN within no more than 0.5 % compared with experimental results, which confirms once again the reliability of this method. It should be noted not only good accuracy of the obtained results but also low computational and time costs when using the GGA + U method. For calculations of structural and electronic properties of ZnO/GaN heterostructure, the same method as for bulk crystals was used. Based on the obtained band diagram of heterojunction, the band offsets of ZnO/GaN heterostructure were determined. We have verified that these band offsets are in very good agreement with previous experimental and theoretical results. Thus, we obtained a highly efficient method for calculating the band offsets of ZnO/GaN heterostructure that produces fine accuracy at a rational computational expense.