The influence of As on the optimum nitrogen to gallium ratio required to grow high quality GaN films by molecular beam epitaxy

We have studied the influence of arsenic on the growth and optical properti es of GaN films grown by plasma-assisted molecular beam epitaxy (PA-MBE) un der different stoichiometric conditions. For GaN films grown without arseni c, there is an optimum N to Ga flux ratio, which results in films showing a good morphology and the highest room temperature band edge luminescence ef ficiency. However, with arsenic present, the highest blue and band edge lum inescence efficiency is observed in GaN at a higher N to Ga ratio. The onse t of GaNAs alloy formation is associated with a change in surface morpholog y. This suggests that arsenic is acting as an isoelectronic surfactant duri ng the growth of GaN films by PA-MBE, changing the morphology, the optical properties and nature of the electrically active defects.