Electronic state of Er in sputtered AlN:Er films determined by magnetic measurements

Abstract

The optoelectronic and piezoelectric properties of AlN:Er thin films have been of great recent interest for potential device applications. In this work, the focus is on the electronic state of Er in AlN:Er thin films prepared by reactive magnetron sputtering on (001) p-type Si substrate. X-ray diffraction shows that Er doping expands the lattice and the AlN:Er film has preferential c-plane orientation. To determine whether Er in AlN:Er is present as Er metal, Er2O3, or Er3+ substituting for Al3+, detailed measurements and analysis of the temperature dependence (2 K–300 K) of the magnetization M at a fixed magnetic field H along with the M vs. H data at 2 K up to H = 90 kOe are presented. The presence of Er2O3 and Er metal is ruled out since their characteristic magnetic transitions are not observed in the AlN:Er sample. Instead, the observed M vs. T and M vs. H variations are consistent with Er present as Er3+ substituting for Al3+ in AlN:Er at a concentration x = 1.08% in agreement with x = 0.94% ± 0.20% determined using x-ray photoelectron spectroscopy (XPS). The larger size of Er3+ vs. Al3+explains the observed lattice expansion of AlN:Er.