Paper TF-WeM3
Structural and Magnetic Properties of Anatase Mn-doped TiO₂ Film Synthesized by Atomic Layer Deposition

Wednesday, October 20, 2010, 8:40 am, Room Ruidoso

Transition metal doped semiconductors exhibiting room temperature ferromagnetism are intensely investigated for spintronics applications. Devices leveraging the spin-dependent effects of these materials would allow for increased data processing speeds, decreased power consumption, and improved integration densities in comparison to standard charge-based electronics. In the past ten years, experimental and computational studies have demonstrated room temperature ferromagnetism (RTFM) for several TiO₂-based dilute magnetic semiconductors (DMSs) namely TiO₂ doped with Mn, Cr, Fe, and Co. Most DMS TiO₂ films are synthesized via sol-gel, pulsed laser deposition (PLD), and plasma-assisted molecular beam epitaxy (PAMBE). Atomic layer deposition (ALD) of DMS TiO₂ has never been demonstrated, although this method has been used to deposit Mn-doped ZnO with DMS properties. ALD circumvents complications with solvent and byproduct removal and with calcination-induced shrinkage that arise during sol-gel synthesis. PLD and PAMBE are ill-suited to the high throughput requirements of commercial manufacturing. In addition, PLD can result in high particulate composition and uneven coverage, while PAMBE films suffer from thickness-dependent morphologies. ALD avoids such problems. The present work involves the synthesis of Mn-doped anatase TiO₂ (0 to 5 at% Mn) thin films on Si(100) via ALD at 200°C and 400°C. Ti(OCH(CH₃)₂)₄ and H₂O are utilized as ALD precursors and Mn(DPM)₃ as a dopant source. The effect of substrate temperature, number of cycles, precursor and oxidant injection times, purge time, and distance between sample and delivery tube on film thickness and uniformity have been investigated. X-ray photoelectron spectroscopy measurements indicate that Mn is successfully doped in the TiO₂ matrix and reveal information about film composition and elemental chemical states. Microstructure, crystallinity, bulk density, and roughness were investigated with scanning electron microscopy, x-ray diffraction, and x-ray reflectivity. SQUID magnetometry was used as a probe of RTFM; the bulk density, microstructure, and magnetic moment of the TiO₂ vary with the concentration of Mn. The results provide insight into the properties of DMS TiO₂ synthesized via ALD and underscore the advantages of the technique - precise thickness, compositional control, and higher process throughput - in comparison to alternative techniques of DMS growth.