Sm-doped ZnO grown by pulsed-laser deposition
Yu-Tso Liao1*, Ping-Hong Kao1, Jyun-Han Chen1, Stephen Nair1, Zong-Yuan Lin1, Hsiang-Lin Liu1, Ming-Yau Chern2, Fang-Yuh Lo1
1Department of Physics, National Taiwan Normal University, Taipei, Taiwan
2Department of Physics, National Taiwan University, Taipei, Taiwan
* Presenter:Yu-Tso Liao, email:g0981229367@gmail.com
Samarium-doped zinc oxide (Sm:ZnO) thin films are grown by pulsed-laser deposition (PLD) on c-oriented sapphire substrates with Sm concentration ranging from 0 to 10 atomic percent. The oxygen partial pressure is 3x10-1 mbar and the substrate temperature is 525°C during deposition. The structural, optical, and magnetic properties are reported.
X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman-scattering are applied to study the structural properties, and with increasing Sm content, the c-lattice constant decreased while the crystal quality and grain size decreased. The surface morphology is examined by atomic force microscope (AFM), which shows homogeneous grains and that surface roughness is not related to doping percentage. The optical properties are investigated by optical transmission and photoluminescence (PL) spectroscopies. Transimission spectroscopy shows that Sm:ZnO thin films keep the direct band gap characteristics of ZnO, and the band gap increases slightly with Sm content. PL spectra of Sm:ZnO show strong defect emissions together with near-band-edge emission lines. The magnetic properties are investigated by SQUID and magneto-optical Faraday effect (MOFE) measurements. SQUID measurements show that Sm:ZnO of 1 at.% doping has ferromagnetic characteristics at low temperature, while other films show only paramagnetic characteristics. The ordering temperature of Sm:ZnO of 1 at.% is lower than 150 K. The Faraday rotation angle changes sign for Sm-doped ZnO compared to ZnO, and the Verdet constant at around band gap increases with Sm content.
Keywords: Diluted magnetic semiconductors, Samarium, Zinc Oxide, Pulsed-laser deposition, Thin film