Electron transport in Mn+ implanted GaAs nanowires

Mn-doped GaAs semiconductors have generated great interest in cur-rent research regarding the evolution from a paramagnetic insulator toa ferromagnetic metal governed by a carrier mediated exchange interac-tion. The interplay between the charge carriers in a semiconductor andthe electron spin of incorporated ferromagnetic metals can be utilizedfor novel spin-sensitive spintronic devices. We have fabricated highlyMn-doped, single-crystalline GaAs nanowires (NWs) by ion implanta-tion at elevated temperatures to facilitate in-situ dynamic annealing.To exploit these nanowires in spintronic applications, a detailed un-derstanding of fundamental charge transport mechanisms is howevernecessary. It is generally expected that new features, dierent fromany bulk counterparts, will emerge in systems with reduced dimen-sionality e.g. quasi-1D NWs. Here we report on a detailed study ofdierent charge transport mechanisms and localization-related eectsin single Mn-doped GaAs NWs in the temperature range from 300K to1.6K, and with magnetic elds ranging from 0T to 8T. In general, theresistance of the nanowires increases strongly from a few M* at 300Kto several G* at 1.6 K. More specically, the temperature dependencedisplays several dierent interesting regimes described by distinctly dif-ferent models. Furthermore, the current-voltage (I-V) characteristicsbecomes strongly non-linear as the temperature decreases and showsapparent power-law behavior at low temperatures. In particular, weinterpret our transport data in the temperature range from 80K to275K in terms of a variable range hopping process inuenced by Mn-induced disorder in the NWs. Below 50K the magnetotransport datareveals a large negative magnetoresistance (MR) under both paralleland perpendicular magnetic elds. We are presently developing modelsto explain this large MR signal, including low-temperature transportmechanisms and possible magnetic interaction between Mn ions.