Manipulation of Room Temperature Ferromagnetic behavior of GaMnN Epilayers
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1198-E07-13
Manipulation of Room Temperature Ferromagnetic behavior of GaMnN Epilayers N. Nepal1, M. Oliver Luen1, P. Frajtag2, J. M. Zavada1, S. M. Bedair1, and N. A. El-Masry2 1 2
Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695 USA Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695 USA
ABSTRACT We report on metal organic chemical vapor deposition growth of GaMnN/p-GaN/n-GaN multilayer structures and manipulation of room temperature (RT) ferromagnetism (FM) in a GaMnN layer. The GaMnN layer was grown on top of a n-GaN substrate and found to be almost always paramagnetic. However, when grown on a p-type GaN layer, a strong saturation magnetization (Ms) was observed. Ms was almost doubled after annealing demonstrating that the FM observed in GaMnN film is carrier-mediated. To control the hole concentration of the p-GaN layer by depletion, GaMnN/p-GaN/n-GaN multilayer structures of different p-GaN thickness (Xp) were grown on sapphire substrates. We have demonstrated that the FM depends on the Xp and the applied bias to the GaN p-n junction. The FM of these multilayer is independent on the top GaMnN layer thickness (tGaMnN) for tGaMnN >200 nm and decreases for tGaMnN < 200 nm. Thus the room temperature FM of GaMnN i-p-n structure can also be controlled by changing Xp and tGaMnN in the GaMnN i-p-n structures.
INTRODUCTION Spin injection into the semiconductor from a ferromagnetic metal suffers with interfacial scattering and has low injection efficiency due to difference in conductivity between ferromagnetic metal and semiconductor. One of the possible solutions is to use dilute magnetic semiconductor (DMS), which exploits both charge and spin of electrons. Advances have been made on GaMnAs based DMS devices. Yamanouchi et al. have demonstrated magnetization reversal in GaMnAs based devices using current pulses in the absence of magnetic field [1]. Slow switching speed and low ferromagnetic transition temperature were the practical limitation for those devices. Low temperature tunneling anisotropic magnetoresistance in molecular beam epitaxy (MBE) grown GaMnAs/GaAs/GaMnAs stack has been reported [2]. The operating temperature of GaMnAs based devices is low for practical application. However, GaMnN film was found to exhibit a range of Tc above room temperature [3-4] and can be used in the room temperature (RT) spintronic devices. Many theoretical and experimental investigations have been carried out on the ferromagnetism (FM) of GaMnN film [3-6]. The FM in GaMnN film could be due to RudermanKittel-Kasuya-Yosida (RKKY)/Zener indirect exchange interaction by itinerate holes (hole mediated) based on mean field approximation [3]. Doping with the shallow Mg acceptor has enhanced the FM of GaMnN films [7]. The exchange interaction between Mn ions and holes would result in ferromagnetic behavior of the GaMnN film. To increase the hole concentration and hence saturation magnetization of the GaMnN film, various schemes have been used [7-8]. However, G
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