High quality heteroepitaxial AlN films on diamond

Heteroepitaxial AlN films grown on (100)- and (111)-oriented diamond (Cα) substrates by plasma-induced molecular beam epitaxy have been investigated by x-ray diffraction (XRD) and atomic force microscopy (AFM). High quality epitaxial growth of almost strain-free wurtzite AlN is observed for both orientations. For the AlN/Cα(111) heterostructures, the epitaxial orientation relationship (0001)[101-bar0] AlN parallel (111)[011-bar] Cα is obtained. However, a significant fraction of up to 20% of the epitaxial layer is oriented differently with (101-bar1) AlN parallel(111) Cα. In case of AlN on Cα(100), a double-domain structure with either (0001)[101-bar0] AlNI parallel (100)[011] Cα or (0001)[1-bar21-bar0] AlNII parallel (100)[011] Cα is found. The linewidths of the XRD ω and 2θ/ω scans of the symmetric AlN 002 reflection have been determined as 1.4 and 0.17 deg. for AlN/Cα(100), 0.55 deg. and 0.11 deg. for AlN/Cα(111), as well as 0.51 and 0.05 deg. for an AlN/sapphire (0001) reference sample grown under similar conditions. Thus, the crystal quality of AlN on Cα(111) is close to that of AlN on sapphire. The corresponding AlN rms roughness values found by AFM are 1.9 nm on Cα(100), 1.7 nm on Cα(111), and 3.2 nm on sapphire (0001), respectively