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 similar to 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 similar to 3.28 to 4.45 eV with Mg content 0 <= x <= 0.51 and from similar to 5.55 to 6.7 eV for Mg content 0.55 <= x <= 1 with a sudden jump of similar to 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.

Automated summary

MgxZn1-xO thin films with wide range bandgap tunability from approximately 3.28 to 6.7 eV were grown on (0001) Sapphire substrates using RF magnetron co-sputtering method. The bandgap of MgxZn1-xO increased gradually from around 3.28 to 4.45 eV with Mg content 0 <= x <= 0.51 and from around 5.55 to 6.7 eV for Mg content 0.55 <= x <= 1, with a sudden jump of about 1.1 eV at x > 0.51. The structure of the MgxZn1-xO films exhibited hexagonal wurtzite phase for Mg content x <= 0.51 and cubic rock salt phase for Mg content >= 0.55, without any mixed phase. X-ray absorption near edge structure (XANES) measurements showed distinct changes in the spectra for wurtzite phase with Mg content x = 0.09, indicating a phase transformation, while no significant change was observed for the cubic phase with Mg content x = 0.73. EXAFS measurements revealed the presence of sixfold Zn coordination in the wurtzite phase of high Mg content MgxZn1-xO films, along with distortion in the bond lengths of Zn-O and Zn-Zn/Mg pairs.