Epitaxy of Zn2TiO4 (1 1 1) thin films on GaN (0 0 1)

High-permittivity spinel Zn2TiO4 thin films were grown on GaN (0 0 1) by rf-sputtering. Grazing-angle, powder, and pole-figure X-ray diffractometries (XRD) were performed to identify the crystallinity and the preferred orientation of the Zn2TiO4 films. Lattice image at the Zn2TiO4 (1 1 1)/GaN (0 0 1) interface was obtained by high-resolution transmission-electron microscopy (HR-TEM). An oxygen atmosphere in sputtering and post heat-treatment using rapid thermal annealing effectively enhanced the epitaxy. The epitaxial relationship was determined from the XRD and HR-TEM results: ( 1   1   1 ) Zn 2 TiO 4 | | ( 0   0   1 ) GaN , ( 2   0   2 ¯ ) Zn 2 TiO 4 | | ( 1   1   0 ) GaN , and [ 2   1 ¯   1 ¯ ] Zn 2 TiO 4 | | [ 0   1 ¯   1   0 ] GaN . Finally, the relative permittivity, interfacial trap density and the flat-band voltage of the Zn2TiO4 based capacitor were ∼18.9, 8.38 × 1011 eV−1 cm−2, and 1.1 V, respectively, indicating the potential applications of the Zn2TiO4 thin film to the GaN-based metal-oxide-semiconductor capacitor.