Origin of unintentional gallium incorporation into AlN layers grown by metalorganic vapor phase epitaxy

This paper presents the origin of gallium (Ga) incorporation into AlN layers grown by metalorganic vapor phase epitaxy (MOVPE). We systematically investigated Ga incorporation from GaN deposits on the inner walls of a growth reactor and an underlying GaN layer. The Ga incorporation is not affected by the GaN deposits on the inner walls of the reactor, but is strongly affected by the underlying GaN layer. We found that the AlN layer incorporates Ga atoms which are desorbed from the underlying GaN layer, and the Ga incorporation decreases with the growth temperature. We conclude that the dominant source of unintentional Ga incorporation into an AlN layer is the underlying GaN layer. Furthermore, we successfully achieved an aluminum composition of over 0.95, almost without unintentional Ga incorporation, by growing the AlN layers at a low temperature.