Tuning of electrical charging effects for ferromagnetic Mn-doped ZnO nanocrystals embedded into a SiO2 layer fabricated by KrF excimer laser irradiation

Abstract

Growth optimization and structural analysis for ferromagnetic Mn-doped ZnO layers deposited by radio frequency magnetron sputtering J. Appl. Phys. 99, 113515 (2006); 10.1063/1.2200768Mn-doped ZnO and (Mn, Cu)-doped ZnO thin films: Does the Cu doping indeed play a key role in tuning the ferromagnetism?The ZnMnO nanocrystals were formed by the laser irradiation of the sputter-deposited ZnMnO ultrathin layer using a 248 nm KrF excimer laser, and the size and density of the nanocrystals were observed to be controllable by modulations of either the energy density or the frequency of the irradiated pulsed-laser beam. Metal-oxide-semiconductor capacitors fabricated using ZnMnO nanocrystals clearly showed the electrical charging effect, and it was observed that the memory window depends on the size and density of nanocrystals. For measurements of the spontaneous magnetization, ZnMnO nanocrystals showed to have room-temperature ferromagnetism with M r of ϳ1.5 emu/ cm 3 and H c 167 Oe. By using ferromagnetism in ZnMnO nanocrystals, tuning of the memory window was demonstrated. Namely, it was clearly observed that the flat-band voltage shift of ϳ1.25 V can be modulated to be ϳ0.8 V by applying the magnetic field. This is attributed to the modulation of probabilities for tunneling events due to the increased magnetoelectrical repulsion between spin-polarized carriers in ZnMnO dilute magnetic semiconductor nanocrystals and unpolarized carriers in p-Si under the magnetic field. These results suggest that ZnMnO nanocrystals can be used for spin-functional memory devices.

Mn-doped ZnO nanocrystals embedded in Al2O3: structural and electrical properties

“…This C-V behaviour is similar to MIS memories with floating gates based on CdSe NC embedded in SiO 2 [42]. Previous work on ZnO embedded in MIS capacitors performed by other groups [4,43] demonstrated that the flat band shift was <1.5 V. The flat band voltage shift obtained from our samples is larger than the previously reported one, which could be explained by the large concentration of NCs or a better retention system. Also notice that the C-V curves might be influenced by the defects at the NCs/Al 2 O 3 interface and even inside the ZnMnO NCs, which could also contribute to the voltage shift.…”