Epitaxial Growth and Properties of Magnetically Doped ZnO Prepared by Pulsed Laser Deposition of Nanoparticle Targets
EMSL Project ID
19394
Abstract
Semiconductor spintronics has the potential to create entirely new paradigms for analog and digital electronics which may have a significant impact on energy consumption and efficiency. However, in order for the field to mature technologically, new classes of materials must be discovered, understood, and utilized in device architectures. One such class of materials is ferromagnetic semiconductors which exhibit carrier spin polarization at and above room temperature. We propose to investigate a promising oxide semiconductor, ZnO, doped with pairs of dopants designed to provide both unpaired ion spins and free carriers to couple these spins. Epitaxial films of ZnO doped with: (i) Co plus interstitial Zn (Znint), and, (ii) Mn plus substitutional N will be grown by pulsed laser deposition in the EMSL using nanoparticle targets synthesized by direct chemical methods at UW, as well as by metal organic chemical vapor deposition. In these two materials systems, the first dopant is the source of unpaired spins and the second dopant provides free carriers to magnetically couple the unpaired spins. Using compositionally homogeneous nanoparticles as laser ablation targets will maximize the homogeneity of the epitaxial films. This choice of dopant pairs is based on our recent demonstration of room-temperature ferromagnetism (RTFM) in (Co,Znint):ZnO and (Mn,N):ZnO, but not in the inverse systems - (Co,N):ZnO and (Mn, Znint):ZnO. We have correlated the observation of RTFM with the resonances Co(II) _ Co(I) + e-CB and Mn(II) _ Mn(III) + h+VB, where e-CB and h+VB originate from donors associated with Znint and N acceptors, respectively. The resonance of Co with e-CB is evidence for strong hybridization of Co with the conduction band whereas the resonance of Mn with h+VB reveals hybridization of Mn with the valence band. Hybridization between magnetic and electronic dopants is a theoretical requirement for thermally robust ferromagnetism and carrier spin polarization in a doped semiconductor. After growth, the materials will be characterized by XPS, VSM, XRD, TEM, RBS/channeling, and AFM in the EMSL, as well as XANES and EXAFS at the Advanced Photon Source (APS) at Argonne National Laboratory. The detailed material properties will be compared to electronic transport and magnetic properties. The latter will include x-ray magnetic circular dichroism (XMCD) at the APS in order to determine exchange splitting in unoccupied states, along with optical MCD at UW. Property determination at this level of depth will allow structure-function relationships to be determined with an unprecedented level of detail.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2006-07-21
End Date
2009-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Chambers SA, TC Droubay, CM Wang, KM Rosso, SM Heald, SA Schwartz, KR Kittilstved, and DR Gamelin. 2006. "Ferromagnetism in Oxide Semiconductors ." Materials Today 9(11):28-35.
Johnson CA, A Cohn, TC Kaspar, SA Chambers, GM Salley, and DR Gamelin. 2011. "Visible-light photoconductivity of Zn1-xCoxO and its dependence on Co2+ concentration." Physical Review. B, Condensed Matter 84(12):Article No. 125203. doi:10.1103/PhysRevB.84.125203
Johnson CA, KR Kittilstved, TC Kaspar, T Droubay, SA Chambers, GM Salley, and DR Gamelin. 2010. "Mid-Gap Electronic States in Zn1 xMnxO." Physical Review. B, Condensed Matter 82(11):Art. No. 115202.
Li Y, TC Kaspar, T Droubay, AG Joly, P Nachimuthu, Z Zhu, V Shutthanandan, and SA Chambers. 2008. "A Study of H and D doped ZnO epitaxial films grown by pulsed laser deposition." Journal of Applied Physics 104(5):,
Li Y, TC Kaspar, T Droubay, Z Zhu, V Shutthanandan, P Nachimuthu, and SA Chambers. 2008. "Electronic properties of H and D doped ZnO epitaxial films." Applied Physics Letters 92(15):Art. No. 152105.