Structural and photoluminescence properties of Gd implanted ZnO single crystals

Abstract

We present the structural and photoluminescence properties of 30 keV gadolinium implanted and subsequently annealed zinc oxide (ZnO) single crystals. Rutherford backscattering and channeling results reveal a low surface region defect density which was reduced further upon annealing. For low implantation fluence, around 85% of the Gd atoms are estimated to be in sites aligned with the ZnO lattice, while for higher fluences the Gd is largely disordered and likely forms precipitates. The Raman spectra of the implanted samples show defect-induced modes, which match the one-phonon density of states for the most heavily implanted samples. Annealing eliminates these features implying the removal of Gd-associated lattice disorder. Low temperature photoluminescence spectra revealed a red-shift in the defect emission, from green to orange/yellow, indicating the suppression of a deep level, which is thought to be due to oxygen vacancies. It is suggested that the orange/yellow emission is unmasked when the green emission is quenched by the presence of the implanted Gd atoms.

Magnetic Properties of Gadolinium-Doped ZnO Films and Nanostructures

“…Ferromagnetism was observed in Gd-doped ZnO films and nanostructures prepared by different methods [15][16][17][18][19][20], which can be further improved by annealing [17,18]. ZnO single crystals implanted with Gd atoms exhibited saturation moments of up to 1.8μ B /Gd [15].…”

Defect-band mediated ferromagnetism in Gd-doped ZnO thin films

“…18 The RBS measurements indicated Gd substitution onto Zn tetrahedral sites. 19 Near edge X-ray absorption fine structure (NEXAFS) spectra at the O K-edge and Gd M 5,4 -edges (Figs. 1(c) and 1(d)) also indicated substitution of Gd in ZnO.…”

Identifying the influence of the intrinsic defects in Gd-doped ZnO thin-films

“…In addition, Gddoped/implanted ZnO exhibited room temperature (RT) ferromagnetic behavior that has been attributed to defect/impurity bands mediated by Gd dopants. [7][8][9][10][11][12] Another interesting phenomenon that has been observed in Gd-doped ZnO is a Kondo-like effect, occurring due to a coupling between carriers and localized spin. 13 More specifically, the electrostatic tuning of Kondo effect in Gd-doped ZnO was demonstrated for electrical-double layer transistor applications.…”

“…11 For ZnO materials, the trivalent RE 3þ ions are found to preferentially occupy substitutional or slightly displaced Zn sites. 11,12,14 However, thus far, few detailed investigations of the effect of growth conditions on the optical and structural properties of RE in situ doped ZnO have been carried out.…”