Effects of Al and N2 Flow Sequences on the Interface Formation of AlN on Sapphire by EVPE

The interface formation mechanisms of AlN films on sapphire substrates grown by the elementary source vapor phase epitaxy (EVPE) method, which is a new AlN bulk fabrication method using Al and N-2 as precursors, are investigated. Supplying N-2 after the substrate temperature reaches the growth temperature [Process N-2(GT)] causes the interface to become rough due to the thermal decomposition of sapphire. Self-separation occasionally occurs with the Process N-2(GT), suggesting that the rough interface generates self-separating films with little strain. On the other hand, supplying N-2 beginning at room temperature forms a relatively smooth interface with voids, which can be realized by the reaction between a nitrided sapphire surface and an Al source.