Scanning Tunneling Microscopy Study of Cr-doped GaN Surface Grown by RF Plasma Molecular Beam Epitaxy
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0892-FF04-03.1
Scanning Tunneling Microscopy Study of Cr-doped GaN Surface Grown by RF Plasma Molecular Beam Epitaxy Muhammad B. Haider, Rong Yang, Hamad Al-Brithen, Costel Constantin, Arthur R. Smith*, Gabriel Caruntu1, and Charles J. O’Connor1. Condensed Matter and Surface Science Program, Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA 1 Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148, USA
Abstract: Cr doped GaN was grown by rf N-plasma molecular beam epitaxy on sapphire (0001) at a sample temperature of 700 oC. Cr/Ga flux ratio was set to a value from 5% to 20%. Subsequently, scanning tunneling microscopy was performed on these surfaces. Cr incorporates on the GaN surface at 700 oC at a Cr concentration of 5% and less. By increasing the Cr/Ga flux ratio to 20% in CrGaN, linear nano structures were formed on the surface, which were not observed on the bare GaN surface. The RHEED and STM studies reveal that Cr atoms form 3×3 reconstruction when 0.1 ML of Cr was deposited at room temperature on 1×1 adlayer of Ga on GaN (000-1). Cr substitutes Ga on the surface when deposited at 700 oC on the MBE grown GaN (000-1) surface for all the experiments, which we have performed, provided the Cr concentration is low (~5%). PACS: 75.50.Pp, 81.15.Hi, 61.10.Nz, 61.14.Hg
Introduction For last two decades, spintronics has become a field of wide interest, where not only the charge but also spin degree of freedom of the charge carriers will be manipulated. Successful spin injection into existing semiconductor-based devices at room temperature is still being investigated. Many scientists have predicted that some Nitride Dilute Magnetic Semiconductors (NDMS) can be used as spin injectors at room temperature. According to Sato et al., based on their first-principles calculations in mean field approximation, CrGaN has a stable ferromagnetic state at Cr concentration above 2%, provided Cr substitutes Ga in GaN lattice [1]. Cr incorporation and Cr substitution at Ga lattice site is not an easy task to investigate using bulk techniques. Scanning Tunneling Microscopy (STM) is an important tool to investigate the Cr incorporation and position in the GaN lattice at atomistic scale. Recently a few results have been reported about the growth and bulk properties of CrGaN. Lee et al. have used ion implantation of Cr on Mg doped MOCVD grown GaN on sapphire substrate [2]. Park et al. performed the growth of Cr doped GaN single crystal by sodium flux method [3]. There are a few reports about the growth and above room temperature ferromagnetism in CrGaN samples, which were grown on sapphire (0001) by electron-cyclotron plasma-assisted molecular beam Epitaxy (MBE) [4,5,6]. We have recently performed a systematic growth study and have observed the effect of Ga/N flux ratios on the structural and magnetic properties of CrGaN and have found the growth *
Corresponding author: [email protected]
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conditions, which resulted in above room temperature ferromagnetism [7].
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