High-quality AlN epitaxial films with atomically smooth surface on Si substrates via inducing ultrathin crystal nucleation seed layer by combined pretreatment

High-quality AlN films were achieved on p -Si(111) substrates with a combined pretreatment using TMAl and NH 3 in the initial stage of heteroepitaxial growth of metalorganic chemical vapor deposition procedure. We demonstrated that the combined pretreatment enables the formation of an ultrathin AlN crystal nucleation seed layer on the Si(111) substrate surface. This layer effectively suppresses the formation of amorphous Si x N y impurities on Si surface and provides abundant uniform nucleation sites for subsequent AlN epitaxial growth, thus greatly improving crystalline quality of thin films. Benefiting from the pretreatment, pits on AlN surface are eliminated and an atomically smooth surface is achieved with a root-mean-square roughness of only 0.274 nm over a 5 µm ×5 µm scanned area. The full width at half maximum of AlN (002) X-ray rocking curve is reduced to 0.26°. A photodetector based on AlN/ p -Si heterojunction exhibits outstanding photodetection performance with low dark current and high photo-to-dark current ratio of 3.25 × 10 3 in vacuum UV wavelength region.