New approaches for calculating absolute surface energies of wurtzite (0001)/(0001¯): A study of ZnO and GaN

Abstract

The accurate absolute surface energies of (0001)/(0001 ̅ ) surfaces of wurtzite structures are crucial in determining the thin film growth mode of important energy materials. However, the surface energies still remain to be solved due to the intrinsic difficulty of calculating dangling bond energy of asymmetrically bonded surface atoms. In this study, we used a pseudo-hydrogen passivation method to estimate the dangling bond energy and calculate the polar surfaces of ZnO and GaN. The calculations were based on the pseudo chemical potentials obtained from a set of tetrahedral clusters or simple pseudo-molecules, using density functional theory approaches. And the surface energies of (0001)/(0001 ̅ ) surfaces of wurtzite ZnO and GaN we obtained showed relatively high self-consistencies. A wedge structure calculation with a new bottom surface passivation scheme of group I and group VII elements was also proposed and performed to show converged absolute surface energy of wurtzite ZnO polar surfaces, and the result were also compared with the above method. These calculations and comparisons may provide important insights to crystal growths of the above materials, thereby leading to significant performance enhancements of semiconductor devices.

Hydrogen-surfactant-assisted coherent growth of GaN on ZnO substrate

“…The estimated errors are in the order of a few meV/Å 2 [36]. Still, the early calculations were performed mainly on non-reconstructed surfaces.…”

“…In this paper, we adopted surface reconstructions proposed by early STM observations and first principles calculations [53,57,69,70]. In this paper, we follow our cluster and pseudo molecule method [36] strictly.…”

Stability of wurtzite semipolar surfaces: Algorithms and practices

“…In the past decades, despite the rapid development in wurtzite (WZ) based semiconductors that led to broad industrial applications, [1][2][3][4][5][6] high quality crystal growth and nanocrystal morphology controlling are challenging [7][8][9][10]. And the display technology based on quantum dots light-emitting diodes (LEDs) is towards the dawn of commercialization.…”

“…Absolute surface energy is one of the key quantities in surface studies. [9,[29][30][31][32] A complete set of knowledge of absolute formation energies of GaN surfaces with all possible orientations is necessary for the related thermodynamic stability analyses, for example, determining the equilibrium crystal shape (ECS) by Wulff's theorem [33]. Such thermodynamic property is one of the key factors in understanding and controlling the growth of GaN nanostructures, which are considered as the major candidates for realizing broadband and multi-color emission [34][35][36][37][38][39][40][41].…”

“…Recently, we developed accurate and efficient approaches (passivation scheme) in the calculations of absolute surface energy of WZ polar surfaces [9,31,32], namely (0001)/(0001 ̅ ). A working algorithm for semi-polar surfaces is missing.…”