Local zincblende coordination in heteroepitaxial wurtzite Zn1−xMgxO:Mn thin films with 0.01 ≤ x ≤ 0.04 identified by electron paramagnetic resonance

Abstract

Zn_1−xMg_xO:Mn thin films with atomic Mg content x below about 0.3 are well known to crystallize in the hexagonal wurtzite structure. Here we demonstrate that beginning with a chemical Mg content of already x = 0.01 in heteroepitaxial Zn_1−xMg_xO:Mn thin films, a local cubic zincblende coordination of the Mn ion can be identified using electron paramagnetic resonance of Mn²⁺ ions. The appearance of a cubic Mn²⁺ spectrum in the wurtzite (Zn,Mg)O films is attributed to an enhanced formation of stacking faults providing zincblende structure locally. The Mn²⁺ ions are incorporated at zinc lattice sites into the Zn_1−xMg_xO films and their zero field spitting allows to monitor even small structural changes in the MnO₄ tetrahedrons. Alloying with the smaller Mg²⁺ ions leads to a shrinking of the Mn–O bond length in dependence on the axial distortion of the parent ZnO₄. Our findings generally show that Mn²⁺ ions in low concentration represent a highly sensitive paramagnetic probe in group II–VI thin films.