Determination of the electronic state of Er in sputtered AlN:Er films by magnetic measurements

The optoelectronic [1] and piezoelectric [2] properties of AlN:Er thin films for device applications have been of great recent interest. The magnitude of optical activity depends on local crystalline environments of Er [3]. Here we focus on the electronic state of Er in AlN:Er (1.6 at.\%) films prepared by reactive magnetron sputtering on Si substrate. X-ray diffraction of the films shows that Er doping expands the lattice and XPS studies confirm the presence of Er. To determine if Er is present as Er metal, Er$_{2}$O$_{3}$ or Er$^{3+}$ substituting for Al$^{3+}$, magnetization was measured vs. temperature (2 K to 300 K) in H = 1kOe and data is found to fit the Curie law with a magnetic moment ${\mu}$ = 4.85 ${\mu}$$_{B}$ per Er, in good agreement with expected value for Er$^{3+}$ substituting for Al$^{3+}$ in AlN [4]. The presence of Er$_{2}$O$_{3}$ and Er metal is ruled out since magnetic transitions expected for Er$_{2}$O$_{3}$ (Er metal) at 3.4 K ({$\sim$}30 K) are not observed, thus establishing that Er substitutes for Al as Er$^{3+}$ in the AlN:Er films.\\[4pt] [1] A.R. Zanatta et al, J. Appl. Phys., 98, 093514 (2005);\\[0pt] [2] V. Narang et al, MRS Symp. Proc. 1519 (2013);\\[0pt] [3] R.G. Wilson et al, Appl. Phys. Lett., 66, 992 (1994);\\[0pt] [4] S. Yang, et al, J. Appl. Phys., 105, 023714 (2009)