Bandgap tunability and local structure of MgxZn1–xO (0 ≤ x ≤ 1) thin films grown by RF magnetron co-sputtering

MgxZn1–xO (0 ≤ x ≤ 1) thin films with wide range bandgap tunability from ~ 3.28 to 6.7 eV were grown on (0001) Sapphire substrates by RF magnetron co-sputtering method. Bandgap of MgxZn1–xO increased monotonously from ~ 3.28 to 4.45 eV with Mg content 0 ≤ x ≤ 0.51 and from ~ 5.55 to 6.7 eV for Mg content 0.55 ≤ x ≤ 1 with a sudden jump of ~ 1.1 eV at x > 0.51. X-ray diffraction measurements revealed the epitaxial nature of MgxZn1–xO thin films in hexagonal wurtzite phase with Mg content x ≤ 0.51 and cubic rock salt phase with Mg content ≥ 0.55 without occurrence of mixed phase. Polarization-dependent XANES measurements showed distinct variations in horizontal and vertical XANES spectra in wurtzite phase of MgxZn1–xO (x = 0.09), while no significant change was observed for the cubic phase of MgxZn1–xO (x = 0.73) confirming phase transformation. However, the local structure around Zn atoms as studied by extended X-ray absorption fine structure (EXAFS) measurements at the Zn K-edge revealed considerable fraction of sixfold Zn coordination in higher Mg content wurtzite phase MgxZn1–xO thin films along with distortion in the bond lengths of Zn–O and Zn–Zn/Mg pairs.