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

Abstract

Gd-doped ZnO thin films were prepared using pulsed laser deposition at different oxygen pressures and varied Gd concentrations. The effects of oxygen deficiency-related defects on the Gd incorporation, optical and structural properties, were explored by studying the impact of oxygen pressure during deposition and post-growth thermal annealing in vacuum. Rutherford Backscattering Spectrometry revealed that the Gd concentration increases with increasing oxygen pressure for samples grown with the same Gd-doped ZnO target. Unexpectedly, the c-lattice parameter of the samples tends to decrease with increasing Gd concentration, suggesting that Gd-defect complexes play an important role in the structural properties. Using low-temperature photoluminescence (PL), Raman measurements and density functional theory calculations, we identified oxygen vacancies as the dominant intrinsic point defects. PL spectra show a defect band related to oxygen vacancies for samples grown at oxygen deficiency. V C 2016 AIP Publishing LLC.

Magnetic Properties of Gadolinium-Doped ZnO Films and Nanostructures

“…The a-parameter increased while the c-parameter decreased with incorporation of Gd compared to without incorporation of Gd. DFT calculations confirmed that Gd-oxygen vacancy (V O ) complexes cause c-parameter contraction [25].…”

“…We attributed this red band to O i and V Zn [32,33]. After a sample was annealed under vacuum conditions to create oxygen vacancies, a significant reduction in the red band was observed, while the spectrum of the vacuum-annealed sample became dominated by the green band (Figure 3(b)) [22,25]. …”

“…The lattice parameters were measured using the extended bond method [24] with the (0 0 4) and (1 0 4) planes. The concentration of Gd increases with oxygen pressure (P d ) [25]. The a-parameter increased while the c-parameter decreased with incorporation of Gd compared to without incorporation of Gd.…”

Bright green emission and temperature dependent localized bound exciton transitions from undoped ZnO films

“…Therefore, the near band edge (NBE) free exciton emission is generally considered as an origin of UV emission in the room temperature PL spectra [4]. The well-known defect-based green emission band in ZnO PL spectra is ascribed to singly ionized oxygen vacancies by some and to other defects or impurities by others [5][6][7]. In other words, the exact origin of green emissions is still in dispute, although defects such as oxygen vacancies (V O ), oxygen interstitials (O i ), zinc vacancies (V Zn ), zinc interstitials (Zn i ) and oxide antisites (O Zn ) are suggested as origin of candidates [8].…”

Electronic structure of gadolinium complexes in ZnO in the GW approximation

“…Channeling experiments as well as photoluminescence studies [1,[3][4][5][6][7][8][9][10] indicate, that rare-earth elements in ZnO are preferentially incorporated at cation sites. The incorporation of Gd in the presence of intrinsic defects in ZnO could lead to the formation of stable compounds inside the crystal [11][12][13][14][15][16]. In particular, the formation of such complexes involving gadolinium and oxygen vacancies or zinc interstitials could promote ferromagnetism in ZnO as suggested in Refs.…”