Structural and optical properties of Zn_1-xMg_xO thin films synthesized with metal organic chemical vapor deposition

We present the structural and optical properties of Zn_1-xMg _xO thin films studied using x-ray diffraction (XRD), extended x-ray absorption fine structure (EXAFS), and photoluminescence (PL) measurements. The Zn_1-xMg_xO films on sapphire [0001] substrates were fabricated with metal organic chemical vapor deposition (MOCVD). The XRD measurements showed that the Zn_1-xMg_xO films (x ≤ 0.05) had a wurtzite structure without any MgO phase and were epitaxially grown along the c-axis of the Al₂O₃ substrate. The lattice constant of the Zn_0.95Mg_0.05O film shrank by 0.023 Å, compared with that of ZnO crystals. From the EXAFS measurements on the Zn _1-xMg_xO films at Zn K-edge, we found a substantial amount of distortion in the bond length of Zn-Zn pairs with a small amount of Mg substitution on the Zn site. The PL measurements showed a gradual increment of the main exciton transitions from 3.36 eV (x = 0.0) to 3.57 eV (x = 0.05) at 10 K. We also observed a strong deep-level emission near 2.3 eV from the specimen with x = 0.05.