Investigation of the Structure of 2H-AlN Films on Si(001) Substrates

By conventional transmission electron microscopy (CTEM) investigations on 2H-AlN films grown by plasma-assisted molecular beam epitaxy (MBE) on Si(001) the influence of the offaxis angle of the substrate surface on the film structure was studied. Three types of Si(001) substrates were used: on-axis, ~1°, and ~5° off-axis Si(001) substrates. The AlN layer on an exact oriented Si(001) substrates consists of 3 AlN film domains: two main film domains, AlN1 and AlN2, and a small domain AlN3 at substrate surface defects. Their c-axis orientations are parallel to the caxis of the substrate: [0001]AlN1,2,3||[001]Si. The a-axes of AlN1 and AlN2 rotated by 30° to each other: [11 2 0]AlN1||[01 1 0]AlN2||[1 1 0]Si [3]. The a-axis orientation of AlN3 is [01 1 0]AlN3||[100]Si. In 2H-AlN films grown on off-axis Si(001) substrates (~1° and ~5°) the ratio between the AlN1 and AlN2 film domains changes dramatically as far as a single domain film structure consisting of only AlN1 is reached. The AlN c-axes of all domains on the off-axis substrates are not parallel to the Si c-axis but tilted by the off-axis angle of the Si(001) substrate (~1° respectively ~5°), i.e. [0001]AlN is parallel to the Si(001) substrate surface orientation.