Synthesis and Characterization of GaGdN – Cammy Abernathy
Date: Mon. November 5th, 2007, 12:30 pm-1:30 pmLocation: Rockefeller 221
The past decade has seen a rise in interest in the area of dilute magnetic semiconductors (DMSs). In part, this has been directed by a push towards harnessing the spin of electrons for device usage in the field of spintronics. This field has potential for increased speed, power efficiency and storage density in devices. Although transition metal dopants have been extensively studied in GaN-based DMS materials, rare earth dopants are coming under increasing scrutiny. GaGdN, with a reported colossal magnetic moment, Curie temperature above room temperature, and much lower dopant concentration level than transition metal doped GaN has sparked increased interest in rare earth dopants. In this talk we will review the behavior and stability of GaGdN films deposited by gas-source molecular beam epitaxy. This material is found to be ferromagnetic above room temperature, with magnetization that does not appear to be due to interfacial effects. The amount of Gd incorporated into the films is extremely low and results in highly resistive films. Co-doping with Si shows larger overall magnetic signal and results in a conductive, n-type material, suggesting that Fermi level position influences the magnetic coupling. The films remain ferromagnetic after annealing , though the saturation magnetization drops with increasing annealing temperature. GaGdN and GaCrN films have been exposed to high energy (10 and 40 MeV) proton irradiation using a fluence of 5 x 109 cm–2 to examine the effect on magnetization. Photoluminescence and magnetic measurements showed significant decreases with irradiation. The largest response came from GaGdN, which experienced a 50-60% loss in band edge luminescence and 11-83% loss in magnetic saturation. After annealing the irradiated samples at 500°C under nitrogen plasma, the irradiated films experienced a complete magnetic recovery. This behavior may shed further light on the cause of ferromagnetism in these films. Finally, superlattice structures containing alternating layers of GaGdN and AlN were fabricated and show that the DMS films retained hysteresis when incorporated into 10 nm structures, but did not exhibit magnetic behavior in 2.5 nm layers. This suggests that this material may be suitable for spin-based devices requiring thin layers for low power operation.