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