Growth and Characterization of Room Temperature Ferromagnetic Mn:GaN and Mn:InGaN for Spintronic Applications

Abstract

Dilute magnetic semiconductors Mn:GaN and Mn:InGaN showing ferromagnetic behavior at room temperature and above were achieved. Light emitting diode devices doped with Mn via diffusion produced operational devices with ferromagnetic properties at room temperature.

Mn:GaN films were grown by: Mn diffusion into metal organic chemical vapor deposition (MOCVD) grown GaN; ion implantation of Mn into MOCVD grown GaN substrates; and MOCVD growth of Mn:GaN using (Et,Cp)₂ Mn as a Mn precursor. Curie temperatures of these Mn:GaN films ranged from 228 to 520 K, as determined by temperature dependent super conducting quantum interference device (SQUID) and extraordinary Hall effect (EHE) measurements. Ferromagnetic properties were observed over a Mn concentration range of 0.09 — 3.5 % depending on the growth technique used. The Mn:GaN coercivity ranged from 100-1500 Oe, where the saturation magnetization varied from 2 to 45 emu/cm³. The easy axes for these films were determined to be along the c direction (i.e. out of plane). The electrical properties of the Mn:GaN films indicated that the films were highly resistive or n-type. Temperature dependent SQUID and EHE measurements verified the absence of superparamagnetism in the films, confirming the absence of small phase separated particles within the films. XRD and TEM determined that no secondary phases were present in any of the films studied, confirming that the ferromagnetic properties result from a solid solution of Mn in the GaN lattice.

Mn:InGaN films were grown by Mn diffusion into InGaN films and by MOCVD using (Et,Cp)&#8322;Mn as a Mn precursor. All Mn:InGaN films were grown on an undoped GaN template. We report on the room temperature ferromagnetic properties of Mn-doped In[subscript x]Ga[subscript 1-x]N with x < 0.15. The Curie temperatures for these Mn:InGaN films ranged from 300 to 700 K, which was confirmed by temperature dependent SQUID measurements. The ferromagnetic properties were observed in a Mn concentration range of 0.12 &#8212; 8 % depending on how the films were grown. The coercivity of Mn:InGaN films were found to range from 100 - 800 Oe, where the saturation magnetization varied from 1 to 28 emu/cm&#178;. The easy axis of magnetization depends on the stress state of the InxGa1-xN film. The easy axis rotates from in-plane to out of plane by changing the film thickness, thus going from strained to fully relaxed films. For intermediate film thickness a transition region of partially relaxed film was identified with isotropic magnetic behavior. The electrical properties of the Mn:InGaN films indicated that the films were n-type or highly resistive. Temperature dependent SQUID measurements verified the absence of superparamagnetism in the films, confirming the absence of small phase separated particles within the films. XRD and TEM determined that no secondary phases were present in any of the films studied, confirming that the ferromagnetic properties result from a solid solution of Mn in the InGaN lattice.