Enhancement in ferroelectricity in V-doped ZnO thin film grown using laser ablation
- PDF / 529,138 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 29 Downloads / 142 Views
1199-F03-44
Enhancement in ferroelectricity in V-doped ZnO thin film grown using laser ablation Tara Dhakal, Devajyoti Mukherjee, Robert Hyde, Hariharan Srikanth, Pritish Mukherjee and Sarath Witanachchi, Department of Physics and Center of Integrated Functional Materials, University of South Florida, Tampa, FL 33620 ABSTRACT We report evidence of enhancement in ferroelectricity in thin films of vanadium (V) doped ZnO grown at higher oxygen pressure. This process reduces oxygen deficiency and the material becomes very insulating, which in turn lowers the leakage current through the ferroelectric capacitor. 2 at. % V doped ZnO films, with thickness of approximately 1 µm were grown epitaxially on c-cut sapphire (Al2O3) (0001) at a growth temperature of 600°C. X-ray analysis showed the layers to be epitaxial where the (0002) diffraction peak had a rocking curve FWHM below 1°. The films with higher oxygen pressure were more insulating than the one grown with lower oxygen pressure. The saturation polarization doubled when the growth pressure increased from 300 mT to 500 mT. Time gated ICCD imaging of the ablated plasma during various O2 pressures and how it translated to the film quality are presented. INTRODUCTION Wide band gap semiconductor ZnO has sustained research interest for quite some time because of its multifunctionality like ferromagnetism [1], piezoelectricity [2], optoelectronic [3], gas sensing [4], photocatalysis [5] etc. In this work, we look at the piezoelectricity and spontaneous polarization properties of ZnO and how it can be affected by dopants and growth conditions. It has been found that ZnO has the strongest piezoelectric response among the tetrahedrally bonded semiconductors [6]. This property of ZnO makes it a suitable material for technologocial application that require strong electromechanical coupling such as sensors and actuators [7]. Recently, Yang et al. [8, 9] has reported an electromechanical d33 coefficient of Vdoped ZnO to be as high as 110pC/N. This value is an order higher compared to the d33 coefficient of bulk ZnO [10] which is 9.9 pC/N. Yang et. al. further show that the d33 coefficient has a maximum value for 2.5 at. % of V doping. The another significant property due to V doping is reported to be the switchable spontaneous electric polarization. A butterfly like displacement graph is reported as a signature of spontaneous polarization [8]. Doping divalent cation Zn sites by V ions creates a mixed valency as well as strain in the original ZnO hexagonal structure because of the reduced ionic size of vanadium. It is reported that the V ions which replace the Zn sites are in 5+ valency state [9]. The mixed valency creates charge polarity between Zn-O and V-O bonds. This charge polarity and the rotation of the nonlinear V-O bonds w.r.t. Zn-O bonds under electric field gives enhanced ferroelectricity [8]. In addition to V-doping, we need to create highly insulating films to further improve ferroelectric properties by reducing the leakage current. For this, we need to suppress the int
Data Loading...
