Effect of Mn Doping in ZnO Thin Films Deposited by Pulsed Laser Deposition
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Effect of Mn Doping in ZnO Thin Films Deposited by Pulsed Laser Deposition P. Bhattacharya, Rasmi R. Das, J. Nieves, Yu. I. Yuzyuk and Ram S. Katiyar Department of Physics, University of Puerto Rico, San Juan, PR 00931-3343 ABSTRACT Mn doped ZnO thin films were grown using pulsed laser deposition technique on (001) Al2 O3 substrates. The x-ray diffraction data confirmed highly c-axis oriented and hexagonal structure of ZnO and Mn doped ZnO thin films. However, an unidentified secondary peak was observed at very close to ZnO (002) peak. Micro Raman spectra of ceramics as well as thin films showed disorder induced Raman bands besides standard wurtzite ZnO modes. The intensity of several LO modes of ZnO was increased with the increase of Mn concentration. Optical absorption data showed an additional absorption band towards lower than bandgap energy (3 eV) with the increase in Mn content. The incorporation of Mn in ZnO thin films reduced the value of resistivities and mobilities with an increase in carrier concentrations. INTRODUCTION Recently, semiconductor devices based on the control and manipulations of electron spins have drawn considerable attention. Long spin relaxation time, large spin transport distances in semiconductors and various device structures have already been demonstrated [1,2]. Dilute magnetic semiconductors (DMS) are extensively investigated for their potential in combining ferromagnetic and semiconductor properties in a single material [3-4]. The most extensively studied DMS is p-type Ga1-x Mnx As for spintronic related device applications. However, the realization of realistic device operated at room temperature will require a substantial increase in the ferromagnetic transition temperature Tc of Ga1-x Mnx As that is in the range of 110-150 K [4]. Although the origin of magnetization is still debatable, it is believed that the presence of Mn 3d transition ions in this material leads to an exchange interaction between sp band electrons or holes and the d electron spins localized at the magnetic ions, resulting in versatile magnetic field induced functionalities. There is a constant surge to modify ZnO and related wide bandgap semiconductors for application in short-wavelength semiconductor diode lasers [5-6]. It has been experimentally demonstrated that the 3d transition metal atoms are soluble up to several mole fraction (~0.35) in ZnO host, which made it a promising candidate for fabrication of DMS with a high Curie temperature. Mn-doped ZnO can be ferromagnetic with a very high Curie temperature (>300K) as predicted by Dietl et al, if doped in to a p-type [7]. However, Norton et al. [8] reported ferromagnetism was obtained into n-type Sn doped ZnO single crystals by Mn implantation. The Curie temperature of Mn doped crystals was found to be 250 K. The thermal equilibrium solid solubility of Mn is 10 mol% [9] and the electron mass (me) is as large as 0.3 me, which can increase the injected spin carriers in the ZnO thin films doped with Mn. Sato et al [10] demonstrated by the band calcula
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