AVS 52nd International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI+EM-WeA

Paper MI+EM-WeA3
Structural Properties, Lattice Dynamics, and Optical Properties of GaMnN

Wednesday, November 2, 2005, 2:40 pm, Room 204

Session: Magnetic Semiconductors
Presenter: N. Dietz, Georgia State University
Authors: W.E. Fenwick, Georgia Institute of Technology
M.H. Kane, Georgia Institute of Technology
M. Strassburg, Georgia Institute of Technology
A. Asghar, Georgia Institute of Technology
S. Gupta, Georgia Institute of Technology
H. Kang, Georgia Institute of Technology
Z. Hu, Georgia State University
S. Graham, Georgia Institute of Technology
U. Perera, Georgia State University
N. Dietz, Georgia State University
I.T. Ferguson, Georgia Institute of Technology
Correspondent: Click to Email
Dilute magnetic semiconductors (DMS) show promise as spintronic materials because of their electrical and magnetic properties. E.g., GaMnN exhibit ferromagnetism (FM) above room temperature (RT). Application of such materials for RT spintronic devices requires an understanding of the origin of this magnetism, which is still under debate in the literature. Knowledge of the structural properties is essential to determine the origin of the RT FM in GaMnN. Therefore this work provides structural and optical studies of GaMnN to reveal the crystalline quality, lattice dynamics, and some fundamental properties such as the optical constant. Increasing Mn concentration significantly affects long-range lattice ordering. The observation of a local vibrational Raman mode at 669 cm@super -1@ combined with the slight excess of metal components in the growth process and the incorporation of Mn acceptor states favors the formation of nitrogen vacancies. Such vacancies form shallow donor complexes and thus contribute to self-compensation, which may hamper carrier mediation. Raman spectroscopy also revealed a disorder-induced mode at 300 cm@super -1@. The intensity of both modes was found to be weaker by more than one order of magnitude compared to GaMnN grown by MBE or prepared by ion-implantation. This is a consequence of the improved MOCVD growth conditions. Crystalline integrity and the absence of major second phase contributions were confirmed by high resolution X-ray diffraction studies. Atomic force microscopy showed that optimized annealing conditions suppressed the formation of Mn-rich precipitates on the surface. Further investigations on the lattice dynamics and the determination of the optical constants were enabled by infrared reflectance spectroscopy. The GaN E1(TO) phonon frequency linearly increases with Mn composition, which is expressed by (558 + 2.7x) cm@super -1@. Meanwhile the peak values of the infrared dielectric functions of the GaMnN decrease with increasing Mn concentration.