Electronic structure and magnetism of Mn-doped GaN

Abstract

Mn doped semiconductors are extremely interesting systems due to their novel magnetic properties suitable for the spintronics applications. It has been shown recently by both theory and experiment that Mn doped GaN systems have a very high Curie temperature compared to that of Mn doped GaAs systems. To understand the electronic and magnetic properties, we have studied Mn doped GaN system in detail by a first principles plane wave method. We show here the effect of varying Mn concentration on the electronic and magnetic properties. For dilute Mn concentration, d states of Mn form an impurity band completely separated from the valence band states of the host GaN. This is in contrast to the Mn doped GaAs system where Mn d states in the gap lie very close to the valence band edge and hybridizes strongly with the delocalized valence band states. To study the effects of electron correlation, LSDA+U calculations have been performed. Calculated exchange interaction in (Mn,Ga)N is short ranged in contrary to that in (Mn,Ga)As where the strength of the ferromagnetic coupling between Mn spins is not decreased substantially for large Mn-Mn separation. Also, the exchange interactions are anisotropic in different crystallographic directions due to the presence or absence of connectivity between Mn atoms through As bonds.

p -type conductivity in cubic (Ga,Mn)N thin films

“…However, an essential ingredient of this model is a p-type carrier concentration of around 10 20 cm -3 , a value significantly higher than the highest hole concentrations so far obtained in GaN. Furthermore, optical measurements have indicated that the Mn acceptor level lies over 1eV above the valence band maximum in Wurtzite (Ga,Mn)N [9,10], which is in agreement with density-of-states calculations [11]. Therefore, in contrast to the case for (Ga,Mn)As, Mn does not appear to be an efficient acceptor in Wurtzite GaN, and may not be expected to interact strongly with delocalised charge carriers in the conduction or valence bands.…”

What is the Valence of Mn inGa1−xMnxN?

“…Figure 1(a) shows partially filled impurity bands lying deep in the band gap similarly to previous DFT analyses [24,[37][38][39][40][41]. Particularly, Fig.…”

“…Early experimental [34][35][36] and density functional theory (DFT) studies [37][38][39][40][41][42] demonstrated a partially filled impurity band formed deeply in the band gap with a significant Mn d character, suggesting a Mn 3+ (d 4 ) configuration different from the Mn 2+ (d 5 ) one in Ga 1−x Mn x As [43]. Later, both x-ray absorption spectroscopy (XAS) studies [44][45][46] and optical absorption analysis [47,48] also concluded a Mn valence state of 3+ (d 4 ).…”

Transition from ferromagnetism to antiferromagnetism in Ga1−xMnxN

“…Other groups argue that no secondary phase is observed in their single-crystal GaMnN samples that show ferromagnetism [9]. There are also discussions about whether the relevant Mn 3d state has d 4 or d 5 + h character, or whether the d levels are localized in the bandgap or inside the valence band [10].Although many of the issues are still under intensive study, recent ab initio band structure and total energy calculations [11,12,13] seem to agree that Mn 3d levels are located in the gap, and that the interaction between substitutional Mn ions is ferromagnetic (FM) at low Mn concentration. Because previous ab initio studies also find that pure MnN has an AFM ground state [14], an interesting question was raised about how the magnetic and electronic properties of Ga 1−x Mn x N evolve as a function of the Mn concentration x.…”

“…Although many of the issues are still under intensive study, recent ab initio band structure and total energy calculations [11,12,13] seem to agree that Mn 3d levels are located in the gap, and that the interaction between substitutional Mn ions is ferromagnetic (FM) at low Mn concentration. Because previous ab initio studies also find that pure MnN has an AFM ground state [14], an interesting question was raised about how the magnetic and electronic properties of Ga 1−x Mn x N evolve as a function of the Mn concentration x.…”