V-pit pinning at the interface of high and low-temperature gallium nitride growth

Abstract

We have performed a detailed study on the development of V-pits in low temperature GaN, varying the temperature for different precursors and carrier gases, showing that the growth conditions can lead to two growth regimes. From this, and considering surface energies, we have built a theoretical framework for interpreting these data. We can then consider that for one growth regime, the V-pit size is proportional to the thickness of the grown layer, implying that the V-pits are essentially pinned to the high temperature-low temperature interface, and the pit continues to grow larger as the film becomes thicker. In the other regime, the increased surface energy of the V-pit balances the energy of the threading dislocation, and the V-pit maintains a constant size with increasing thickness. These stabilized V-pits are considered unpinned, or "floating". We have shown that increasing temperature and the use of hydrogen rather than nitrogen for the carrier gas favors unpinned V-pits, and can therefore be considered to lower the energy of the (0002) plane versus the preferred inclined plane of {10-11}. These unpinned V-pits are much smaller than those that are pinned, and this is therefore the favored regime for high quality growth interfaces and surface morphology.