Homoepitaxial growth of non-polar AlN crystals using molecular dynamics simulations
Homoepitaxial growth of AlN on (11–20) a-plane and (1–100) m-plane under varying deposition temperatures and aluminum to nitrogen flux ratios was carried out using molecular dynamics (MD) simulations with a Tersoff based interatomic potential. The results indicate that much thicker overgrown films are obtained on m-plane as compared to the a-plane, for the same temperature, N:Al flux, and number of precursor atoms. Crystallinity of the depositions improves as the temperature is increased above 1000 K, accompanied with a better stoichiometry due to increased adatom mobility. Improvement in crystal quality with a N:Al ratio greater than 1 is seen because N atoms desorb more easily than Al atoms. Increasing the N:Al ratio too high limits Al adatom mobility as well as causes site blocking for Al atoms and degrades the deposition quality. The optimum value for N:Al flux ratio was found to be between 1.2 and 1.8 for the deposition temperatures tested based on crystallinity and stoichiometry.
• Growth rate on m-plane AlN is much higher than a-plane AlN surfaces.
• Deposition quality improves substantially as temperature is increased beyond 2000 K.
• Growth rate of crystals drops as temperature of deposition is increased beyond 2500 K.
• The ideal N:Al ratio is found to be between 1.2 and 1.8 for temperatures of 2000 K–2500 K.
• Too high of N:Al ratios results in decreased adatom mobility and site blocking.
Source: Surface Science