Nanoscale ferromagnetism in nonmagnetic doped semiconductors

While ferromagnetism at relatively high temperatures is seen in diluted magnetic semiconductors such as Ga_1−xMn_xAs, doped semiconductors without magnetic ions have not shown evidence for ferromagnetism. Using a generalized disordered Hubbard model designed to characterize hydrogenic centers in semiconductors, we find that such systems may also exhibit a ferromagnetic ground state, at least on the nanoscale. This is found most clearly in a regime inaccessible to bulk systems, but attainable in quantum dots as well as heterostructures. We present numerical results demonstrating the occurrence of high spin ground states in both lattice and positionally disordered systems. We examine how the magnetic phases are affected by characteristics of real doped semiconductors, such as positional disorder and electron-hole asymmetry.