GaMnN dilute magnetic semiconductor samples, prepared by metalorganic chemical vapor deposition, are shown to exhibit ferromagnetism or even paramagnetism depending upon the type and concentration of extrinsic impurity present in the film. In addition, GaMnN deposited using growth parameters normally yielding a nonferromagnetic film becomes strongly ferromagnetic with the addition of magnesium, an acceptor dopant. Based upon these observations, it seems that ferromagnetism in this material system depends on the relative position of the Mn energy band and the Fermi level within the GaMnN band gap. Only when the Fermi level closely coincides with the Mn-energy level is ferromagnetism achieved. By actively engineering the Fermi energy to be within or near the Mn energy band, room temperature ferromagnetism is realized.

We report on the electrical field control of ferromagnetism ͑FM͒ at room temperature in III-N dilute magnetic semiconductor ͑DMS͒ films. A GaMnN layer was grown on top of an n-GaN substrate and found to be almost always paramagnetic. However, when grown on a p-type GaN layer, a strong saturation magnetization ͑M s ͒ was observed. This FM in GaMnN can be controlled by depletion of the holes in the GaMnN/p-GaN/n-GaN multilayer structures. We have demonstrated the dependence of the FM on the thickness of the p-GaN in this heterostructure and on the applied bias to the GaN p-n junction. The M s was measured by an alternating gradient magnetometer ͑AGM͒ and a strong correlation between the hole concentration near the GaMnN/p-GaN interface and the magnetic properties of the DMS was observed. At room temperature an anomalous Hall effect was measured for zero bias and an ordinary Hall effect for reverse bias in a fully depleted p-GaN layer. This is in close agreement with the AGM measurement results.

Dilute magnetic semiconductor films (GaMnN) are highly resistive, making transport measurements difficult to achieve. However, when GaMnN films are sandwiched between p-type doped (AlGaN∕GaN) strained-layer superlattices, holes from the superlattice interact with the Mn3+∕2+ ions and transport measurements were realized. The authors have found also that the ferromagnetic properties of GaMnN critically depend on the level of p-type doping in the superlattice. They report anomalous Hall effect measurements in this (AlGaN∕GaN):Mg∕(GaMnN) multilayered structure. The current results also demonstrate the role of carriers, especially holes, in mediating the ferromagnetic properties of GaMnN dilute magnetic semiconductor films.

We report on the growth and magnetic properties of GaMnN films and p-i-n junctions grown by metalorganic chemical vapor deposition. The magnetic properties of MOCVD grown GaMnN were found to depend upon the type and concentration of the co-dopant. Si or Mg co-doping of GaMnN films led to either ferromagnetic or paramagnetic behavior depending on the concentration. The magnetic properties within the GaMnN material system appear to correlate with the position of the Fermi level. Ferromagnetism was observed only when the Fermi energy level was within or very close to the Mn energy band. The presence of the Fermi energy level within the Mn energy band allows the presence of carriers that mediate ferromagnetism. These results further confirm that the ferromagnetic properties result from a solid solution of Mn in the GaN. Mn-doped GaN p-i-n junctions which were grown to study the effect of the magnetic properties on the I/V characteristics. These devices consist of GaN:Si/GaMnN/GaN:Mg layers grown by metal-organic chemical vapor deposition. The carrier concentrations for the n and p-type layers are ~ 5x10 18 /cm 3 and 1x10 18/cm 3 respectively, where the GaMnN i layer is approximately 0.2-0.45 µm thick with up to 0.5% Mn.