Growth, electronic and magnetic properties of doped ZnO epitaxial and nanocrystalline films

• Published in: Applied physics. A, Materials science & processing Vol. 88; no. 1; pp. 1 - 5
• Main Authors: Chambers, S.A., Schwartz, D.A., Liu, W.K., Kittilstved, K.R., Gamelin, D.R.
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer Nature B.V 01.07.2007
• Subjects: Absorption spectra; Applied physics; Chemical synthesis; Cobalt; Conduction bands; Epitaxial growth; Ferromagnetism; High temperature; Magnetic properties; Magnetism; Materials science; Metalorganic chemical vapor deposition; Nanoparticles; Organic chemicals; Organic chemistry; Oxygen plasma; Room temperature; Spin coating; Wurtzite; Zinc oxide
• DOI: 10.1007/s00339-007-3948-2
• ISSN: 0947-8396

We have used oxygen plasma assisted metal organic chemical vapor deposition along with wet chemical synthesis and spin coating to prepare CoxZn1-xO and MnxZn1-xO epitaxial and nanoparticle films. Co(II) and Mn(II) substitute for Zn(II) in the wurtzite lattice in materials synthesized by both methods. Room-temperature ferromagnetism in epitaxial Co:ZnO films can be reversibly activated by diffusing in Zn, which occupies interstitial sites and makes the material n-type. O-capped Co:ZnO nanoparticles, which are paramagnetic as grown, become ferromagnetic upon being spin coated in air at elevated temperature. Likewise, spin-coated N-capped Mn:ZnO nanoparticle films also exhibit room-temperature ferromagnetism. However, the inverse systems, N-capped Co:ZnO and O-capped Mn:ZnO, are entirely paramagnetic when spin coated into films in the same way. Analysis of optical absorption spectra reveals that the resonances Co(I)↔Co(II)+e-CB and Mn(III)↔Mn(II)+h+VB are energetically favorable, consistent with strong hybridization of Co (Mn) with the conduction (valence) band of ZnO. In contrast, the resonances Mn(I)↔Mn(II)+e-CB and Co(III)↔Co(II)+h+VB are not energetically favorable. These results strongly suggest that the observed ferromagnetism in Co:ZnO (Mn:ZnO) is mediated by electrons (holes).