Differences in optoelectronic properties between H-saturated and unsaturated GaN nanowires with DFT method

Abstract

To investigate the influences of dangling bonds on GaN nanowires surface, the differences in optoelectronic properties between H-saturated and unsaturated GaN nanowires are researched through first-principles study. The GaN nanowires along the [0001] growth direction with diameters of 3.7, 7.5 and 9.5 Å are considered. According to the results, H-saturated GaN nanowires are more stable than the unsaturated ones. With increasing nanowire diameter, unsaturated GaN nanowires become more stable, while the stability of H-saturated GaN nanowires has little change. After geometry optimization, the atomic displacements of unsaturated and H-saturated models are almost reversed. In (0001) crystal plane, Ga atoms tend to move inwards and N atoms tend to move outwards slightly for the unsaturated nanowires, while Ga atoms tend to move outwards and N atoms tend to move inwards slightly for the H-saturated nanowires. Besides, with increasing nanowire diameter, the conduction band minimum of H-saturated nanowire moves to the lower energy side, while that of the unsaturated nanowire changes slightly. The bandgaps of H-saturated nanowires are approaching to bulk GaN as the diameter increases. Absorption curves and reflectivity curves of the unsaturated and H-saturated nanowires exhibit the same trend with the change of energy except the H-saturated models which show larger variations. Through all the calculated results above, we can better understand the effects of dangling bonds on the optoelectronic properties of GaN nanowires and select more proper calculation models and methods for other calculations.