ZnO nanotips, grown on c-$Al_2O_3$ and quartz, were implanted variously with 200 keV Fe or Mn ions to a dose level of $5{\times}10^{16}cm^{-2}$. The magnetic properties of these samples were measured using a superconducting quantum interference device (SQUID) magnetometer. Fe-implanted ZnO nanotips grown on c-$Al_2O_3$ showed a coercive field width of 209 Oe and a remanent field of 12% of the saturation magnetization ($2.3{\times}10^{-5}emu$) at 300K for a sample annealed at $700^{\circ}C$ for 20 minutes. The field-cooled and the zero-field-cooled magnetization measurements also showed evidence of ferromagnetism in this sample with an estimated Curie temperature of around 350 K. The Mn-implanted ZnO nanotips grown on c-$Al_2O_3$ showed superparamagnetism resulting from the dominance of a spin-glass phase. The ZnO nanotips grown on quartz and implanted with Fe or Mn showed signs of ferromagnetism, but neither was consistent.

Magnetic characterization studies of Ni-implanted Al0.35Ga0.65N have been made for various magnetic fields and sample temperatures by using a superconducting quantum interference device (SQUID). Ni ions were implanted at 200 keV to a dose of 3 x 1016 cm(-2) at room temperature. The material was found to show clear signs of ferromagnetism after annealing between 675 and 775 degrees C for 5 min. The ferromagnetic property persisted above room temperature, and a coercive field width of 118 Oe and a remanent field of 16 % of the saturation magnetization of 2.6 x 10(-5) emu were obtained at 300 K after annealing at an optimum annealing temperature of around 750 degrees C. This ferromagnetic property was also confirmed with field-cooled and zero-field-cooled magnetization measurements, and the Curie temperature was estimated to be around 350 K. Cathodoluminescence and X-ray diffraction (XRD) measurements showed that the significant implantation-related damage was recovered after annealing at 750 degrees C, indicating a good Ni incorporation in the Al0.35Ga0.65N. Furthermore, the XRD measurements also showed no indication of secondary phase formation or Ni clusters, which implies that we had observed a dilute ferromagnetic semiconductor behavior.

Fe ions of dose 5x10(16) cm(-2) were implanted at 200 keV into a-plane ZnO epitaxial films. The epitaxial quality of the postannealed samples was verified by x-ray diffraction omega-rocking curves and phi scans, whereas x-ray absorption spectroscopy identified the presence of both Fe2+ and Fe3+ ions, as well as changes in their relative concentration during postannealing. Superconducting quantum interference device measurements show that the as-implanted and postannealed films are ferromagnetic at room temperature. The saturation magnetization reduces during annealing possibly due to the decrease in the number of oxygen vacancies. (c) 2006 American Institute of Physics.

A nominally undoped MBE-grown Al0.35Ga0.65N thin film was implanted with Cr, Mn, and Ni with an energy of 200keV to a dose of 5×1016cm−2 for Cr and Mn and to a dose of 3×1016cm−2 for Ni. The magnetic properties of these samples were measured using a superconducting quantum interference device (SQUID) magnetometer. The Cr-implanted Al0.35Ga0.65N annealed at 750°C has a coercive field (HC) of 178Oe at 300K, and field-cooled (FC) and zero-field-cooled (ZFC) magnetization measurements show evidence of ferromagnetism in this sample with an estimated Curie temperature of around 350K. The Mn-implanted sample has an HC of 180Oe at 300K after annealing at 750°C for 5min, which indicates a dominant ferromagnetic phase. The Ni-implanted Al0.35Ga0.65N produces clear ferromagnetic hysteresis at temperatures up to 350K. FC–ZFC magnetization separation suggests the true presence of ferromagnetism in this material.

We report our progress on the design and fabrication of electrostatically-actuated microelectromechanical (MEM) tunable wavelength filters and vertical cavity surface-emitting lasers (VCSELs). We investigate both an all-semiconductor monolithic approach and a hybrid approach based on the combination of conventional polysilicon microelectromechanical systems (MEMS) and III-V semiconductor thin-film distributed Bragg reflector (DBR) and VCSEL structures. In the tunable hybrid structures the III-V semiconductor layers are flip-bonded onto specially designed polysilicon foundry MEMS structures and separated from their lattice-matched parent substrates by a novel post-bonding lift-off process.

A schematic diagram of a lift-off VCSEL structure designed to emit at 980 nm is shown. All devices herein are grown by molecular beam epitaxy on [001]-oriented GaAs substrates. The VCSELs have a standard triple InGaAs/AlGaAs quantum well active region within a 1 λ-thick microcavity. The distributed Bragg reflectors (DBRs) are composed of GaAs and Al0.9Ga0.1As quarter-wave layers.