Correlations Between Optical Transmission and Magnetic Properties of Doped and Undoped GaMnN
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Correlations Between Optical Transmission and Magnetic Properties of Doped and Undoped GaMnN Amr M. Mahros1, M. O. Luen1, A. Emara1, E. A. Berkman2, F. E. Arkun2, X. Zhang1, J. Muth1, N. A. El-Masry2, and S. M. Bedair1 1 Electrical and Computer Engineering Department, NC State University, Raleigh, NC, 27695 2 Materials Science and Engineering Department, NC State University, Raleigh, NC, 27695 ABSTRACT Ferromagnetism (FM) in GaMnN was found to be related to the position of the Fermi level relative to the Mn deep-level band. The location of the Fermi level can be altered by doping GaMnN with Si (n-type) and Mg (p-type) dopants, resulting in a ferromagnetic to paramagnetic transformation. We have found that this manipulation of the Fermi level also can affect the optical properties of GaMnN, GaMnN: Mg and GaMnN: Si. The major optical absorption bands were found either to be enhanced or diminished depending on the level and nature of the doping elements. Therefore, a correlation between optical properties and saturation magnetization of GaMnN can be established. INTRODUCTION Ferromagnetic GaMnN crystals exhibiting a range of Curie temperatures up to and above room temperature have been synthesized by several different growth techniques [1, 2]. Optical absorption studies on GaMnN films indicate that Mn forms a deep acceptor band with an optical transition at 1.5 eV and broad absorption band that commences at 2.0 eV [3]. Photoluminescence spectra of the same samples show infrared emission at 1.27 eV which further supports the position of the Mn band identified by optical absorption measurements. Others observed that introducing Mn into GaN led to the appearance of a very strong absorption band starting at 1.9 eV and attributed this band to a transition from Mn acceptor states to the conduction band [4]. The absence of the absorption band with a threshold of ~1.5 eV was attributed to the Fermi level being above the Mn band. Additional reports on the optical absorption measurements of the n- type GaMnN and GaMnN:Mg observed an absorption band with a threshold of 2.0 eV tailing to the band edge of GaN. They also observed an additional absorption peak in the infrared region with two sharp peaks at ~ 1.41 eV and 1.48 eV in the case of GaMnN: Mg [5]. these peaks were attributed to an internal transition of the Mn atom followed by thermal ionization to the GaN valance band. EXPERIMENTAL Growth of GaMnN samples was performed on (0001) sapphire substrates by metal organic chemical vapor deposition (MOCVD). Details of the growth reactor and growth conditions are reported elsewhere [1, 2]. Optical transmission measurements were performed using a Varian Cary 5E UV-VIS-IR dual beam spectrometer with a spectral
range between 175 nm and 3.3 µm. All measurements were performed at room temperature. Emission from a tungsten halogen light source was used in-line with a spectrophotometer to scan selectively the wavelengths between 200 nm and 900 nm. Ultraviolet and visible light was detected by a Hamamatsu photomultiplier tub
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