Growth and Characterization of Mn Doped GaN and AlGaN Dilute Magnetic Semiconductors

Abstract

Growth of dilute magnetic semiconductors GaMnN and AlGaMnN showing ferromagnetic behavior above room temperature was achieved. Two approaches were used for Mn doping. GaMnN films were grown by MOCVD using (EtCp2)Mn as the precursor for in-situ Mn doping, while AlGaMnN samples were grown by post growth solid state Mn diffusion into MOCVD grown AlGaN films.

Curie temperatures of the GaMnN films ranged from 270 to above 400K depending on Mn concentration. This dependence of Curie temperature on Mn concentration indicates that the GaMnN films are random solid solutions. Ferromagnetic behavior for these films were observed along c-direction (out of plane orientation) in a Mn concentration range of 0.025-0.25%. The saturation magnetizations ranged between 0.18 and 1.0 emu/cc, fairly high values considering the low levels of Mn doping. SQUID measurements ruled out the possibility of spin-glass and superparamagnetism in these MOCVD grown GaMnN films. Structural characterizations of the GaMnN films were achieved by XRD, SIMS and TEM measurements. XRD and TEM confirmed that the films were single crystal solid solutions without the presence of secondary phases. SIMS revealed that Mn was incorporated homogeneously throughout the GaMnN layer. The samples were highly resistive to be characterized by Hall measurement; however PL measurements showed that the samples were optically active.

For the AlGaMnN films, SQUID and VSM measurements on several samples revealed ferromagnetism above room temperature. SQUID measurements on 30%AlN sample determined a Curie temperature of 320K and confirmed the absence of superparamagnetism. SIMS verified the diffusion of Mn into the AlGaN lattice, and XRD showed no sign of secondary phases. However TEM is necessary to rule out the presence of secondary phases.

This study showed that the growth of III-Nitride films doped with Mn require special growth conditions to achieve ferromagnetism above room temperature, and the grown films do not have to be p-type to exhibit ferromagnetism, but depends on the Fermi position.