Control of hole localization in magnetic semiconductors by axial strain

Abstract

Mn and Fe-doped GaN are widely studied prototype systems for hole-mediated magnetic semiconductors. The nature of the hole states around the Mn and Fe impurities, however, remains under debate. Our self-interaction corrected density-functional calculations show that the charge neutral Mn 0 and positively charged Fe + impurities have symmetry-broken d 5 + h ground states, in which the hole is trapped by one of the surrounding N atoms in a small polaron state. We further show that both systems also have a variety of other d 5 + h configurations, including symmetric, delocalized states, which may be stabilized by axial strain. This finding opens a pathway to promote long-range hole-mediated magnetic interactions by strain engineering and clarifies why highly strained thin-films samples often exhibit anomalous magnetic properties.

Electrical and optical properties of iron in GaN, AlN, and InN

“…The (+/0) levels appear at 0.26 eV above the VBM. Consistent with prior reports [48,49], we find the wave function for the positive charge state localized on the Fe atom and the four nearest-neighbor nitrogen sites. Figure 1 shows that the (0/−) thermodynamic transition level (acceptor level) is located 0.50 eV below the CBM.…”

Strain Engineering to Release Trapped Hole Carriers in p-Type Haeckelite GaN

“…Ideal p-type doping combines high dopability and high carrier mobility, so it is desirable that the extended (delocalized and mobile) states are the thermal ground state compared with the trapped (immobile) states. Considering the fact that small polarons are intimately coupled with the local atomic structure around the impurities, ,, it should be possible to control the multifarious hole states (polaron-X, polaron-Z, and delocalized) of Mg and Be impurities in 4|8-GaN by applying lattice strain. To test this idea, in 4|8-GaN, we apply lattice strain along the z axis.…”

“…Indeed, Mg acceptors exhibit a dual nature , i.e., the hole states have multiple configurations including both trapped (polaronic) and extended (delocalized) states, with the polaronic states lower in energy by ∼30 meV (i.e., hole trapping energy is ∼30 meV). ,− Intriguingly, a strain control of the trapping and detrapping of hole carriers has been demonstrated for a transition metal (TM) doped in w -GaN that switches on and off the magnetic interaction between the TM impurities. , This begs the question of whether a similar strain control exists in 4|8-GaN, which could open a route to achieve sufficient mobile hole carrier concentration for LED devices.…”

“…38,42−47 Intriguingly, a strain control of the trapping and detrapping of hole carriers has been demonstrated for a transition metal (TM) doped in w-GaN that switches on and off the magnetic interaction between the TM impurities. 42,47 This begs the question of whether a similar strain control exists in 4|8-GaN, which could open a route to achieve sufficient mobile hole carrier concentration for LED devices.…”

Out-of-plane magnetic anisotropy in bulk ilmenite $\text{CoTiO}_3$

“…Computational methodology Electronic delocalization within Density Functional Theory may lead to an incorrect description of the magnetic properties. In particular, for systems with localized electrons such as d-electrons of transition metals acting as dopants in semiconductors or taking part of transition metal oxides, correlation effects may lead to qualitatively different results [11][12][13]. The DFT+U method is one approach that aims to correct the tendency of DFT towards itineracy by explicitly treating the Coulomb interaction with a Hubbard-like interaction for a subset of states in the system [9].…”