Optical Properties of Dilute Magnetic Wide-Band-Gap Semiconductor Multilayers and Nanostructures
In this project we investigate magnetism-related optical properties in novel wide band gap semiconductor multilayers and nanostructures. Our research is aimed at better understanding of the dimensionality influence onto magnetism-induced optical properties, where domain wall surface energy, magnetic field configuration energy, and magnetization orientation anisotropy energy may compete differently in quasi-3D and nanostructure configurations. We intend determination of spin polarization, hysteresis behavior, optical transport parameters (longitudinal and transverse mobility, effective mass, and density) of free charge carriers in wide band gap magnetic ion doped diluted magnetic semiconductors as a function of geometry, dimension and composition. Nanostructured thin films and multilayers are prepared by pulsed laser ablation, using substrate prepatterning, self-organization and ion beam etching techniques (see figure).
We perform Magnetooptic Terahertz-to-Farinfrared generalized ellipsometry for optical transport measurements, magnetooptic Raman scattering for spin polarization measurement, and if applicable, magnetooptic Kerr-effect hysteresis measurements. Materials preparation, structural, electrical, and optical characterization are conducted within the NCMN and in collaboration with the University Leipzig, Germany (H. Schmidt, M. Lorenz, Prof. M. Grundmann). The first year will begin with investigations of quasi three-dimensional magnetic properties in wide band gap magnetic ion doped materials grown as thin films. The host materials will be oxide and nitride semiconductors ZnO, GaN, AlN, and InN, with Cr, Mn, Co, or V doping. The first year concerns magnetism-induced optical properties in single layers and heterostructures with thin and ultrathin layer thickness.
SEM images of MgZnO nanowires (PLD) on sapphire:
(a) ZnO nanowire array on Au nucleation pads,
(b) needle-like ZnO nanostructures obtained at reduced laser pulse energy,
(c) aligned hexagonal ZnO nanocrystallites grown at reduced Ar pressure,
(d) microcrystals obtained by successive deposition from ZnO and ZnO:Zn targets,
(e) hexagonal ZnO microdots with top wires on CeO2 buffer layer,
(f) MgZn nanowire array. (Redrawn from Lorenz, Grundmann et al., Appl. Phys. Lett. 86, 143113 (2005)