Influence of initial surface reconstruction on nitridation of Al_2O_3 (0001) using low pressure ammonia

摘要

The purpose of this study is to investigate the effect of initial surface reconstruction on the nitridation process of Al_2O_3 (0001). This was done by exposing differently reconstructed sapphire substrates at different temperatures to low pressure ammonia (NH_3). Structural and chemical analysis were carried out using low-electron energy diffraction and x-ray photoelectron spectroscopy. The experiments revealed that using low pressure ammonia (P_(NH_3) < 1 X 10~(-5) Torr), no nitridation takes place on (1 X 1) unreconstructed surfaces. However, when the unreconstructed surface starts to change to a (31~(1/2) X 31~(1/2))R ± 9° reconstructed surface, with increasing substrate temperature, the nitridation becomes successful. When using the initially reconstructed surface, the nitridation is successful even from the lowest temperature used. These results suggest that the initial surface reconstruction has a major effect on the nitridation process. This kinetic behavior has not been reported before, with most nitridation studies mainly focusing on the effect of surface temperature on the resulting surface morphology, rather than the actual kinetics of the process itself.