Identification of shallow Al donors in Al-doped ZnO nanocrystals: EPR and ENDOR spectroscopy

Abstract

Electron paramagnetic resonance and electron-nuclear double resonance (ENDOR) experiments on ZnO nanoparticles doped with Al reveal the presence of shallow, effective-masslike donors related to substitutional Al atoms. The shallow character of the Al donor is evidenced by the multitude of ENDOR transitions of the $^{67}\text{Z}\text{n}$ nuclear spins and by the hyperfine interaction of 1.45 MHz of the $^{27}\text{A}\text{l}$ nuclear spin, which is much smaller than for atomic aluminum. The electric-field gradients at the Al and Zn atoms are found to be nearly the same, which supports the contention that the Al atom is located at a Zn position.