2 00 3 Laser ablation of Co : ZnO films deposited from Zn and Co metal targets on ( 0001 ) Al 2 O 3 substrates

Laser ablation of Co:ZnO films deposited from Zn and Co metal targets on (0001) Al 2 O 3 substrates. Abstract We report on the synthesis of high-quality Co-doped ZnO thin films using the pulsed laser deposition technique on (0001)-Al 2 O 3 substrates performed in an oxidizing atmosphere, using Zn and Co metallic targets. We firstly optimized the growth of ZnO in order to obtain the less strained film. Highly crystallized Co:ZnO thin films are obtained by an alternative deposition from Zn and Co metal targets. This procedure allows an homogenous repartition of the Co in the ZnO wurzite structure which is confirmed by the linear dependance of the out-of-plane lattice parameter as a function of the Co dopant. In the case of 5% Co doped, the film exhibits ferromagnetism with a Curie temperature close to the room temperature. 1 Diluted Magnetic Semiconductors (DMS) of III-V or II-VI types have been obtained by doping semiconductors with magnetic impurities (Mn for example) 1,2. These materials are very interesting due to their potential applications for spintronics 3. However, the low Curie temperature (T C) has limited their interest 4. Based on the theoretical works of Dietl et al. 5 , several groups 6 have studied the growth of Co-doped ZnO films 7–10 which is a good candidate having a high T C 5. Using pulsed laser depositions (PLD), Ueda et al. reported ferromagnetism (FM) above room temperature 7 , while Jin et al. found no indication of FM by utilizing laser molecular beam epitaxy 8. This controversy between research teams may result from the growth method used and/or from the growth conditions (oxygen pressure, deposition temperature, etc...). In the particular case of the PLD technique, it may also arise from the targets preparation and this parameter has never been considered up to now. One of the reason is that the control of the dopant incorporation would be quite difficult to obtain using a pre-doped ceramic oxide target 11. This is a crucial point since the properties of the DMS are very sensitive to the percentage of dopant 12. The homogenity of dopant incorporation as well as the precise control of the growth might be responsible for the changes in the physical properties of the films obtained by the different groups. Therefore, the objective of this investigation is two fold : first to develop an accurate method to grow the Co:ZnO films with …