%0 Journal Article
%T Thermoelectric Characterization of Electronic Properties of GaMnAs Nanowires
%A Phillip M. Wu
%A Waldomiro Paschoal Jr.
%A Sandeep Kumar
%A Christian Borschel
%A Carsten Ronning
%A Carlo M. Canali
%A Lars Samuelson
%A H£¿kan Pettersson
%A Heiner Linke
%J Journal of Nanotechnology
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/480813
%X Nanowires with magnetic doping centers are an exciting candidate for the study of spin physics and proof-of-principle spintronics devices. The required heavy doping can be expected to have a significant impact on the nanowires' electron transport properties. Here, we use thermopower and conductance measurements for transport characterization of Ga0.95Mn0.05As nanowires over a broad temperature range. We determine the carrier type (holes) and concentration and find a sharp increase of the thermopower below temperatures of 120£¿K that can be qualitatively described by a hopping conduction model. However, the unusually large thermopower suggests that additional mechanisms must be considered as well. 1. Introduction Self-assembled semiconducting epitaxial nanowires are promising building blocks for field effect transistors [1], sensors [2], and solar cells [3]. An exciting new direction, which has recently been shown to be possible due to successful incorporation of magnetic Mn dopants into epitaxially grown GaAs nanowires (NWs) [4¨C11], is their use for proof-of-concept spintronics devices [12]. The doping techniques are advancing rapidly, and it has recently been shown that ion beam implantation can produce single crystalline, homogeneously doped GaMnAs NWs [13]. Furthermore, a recent study found that the Curie temperature of GaMnAs nanostrips could be enhanced to 200£¿K with nanostructure engineering [14], suggesting the possibility for nanowire-based devices to operate at higher temperatures compared to thin films or bulk. In addition to the exciting possibilities for application, from the fundamental point of view, ferromagnetic NWs will provide an opportunity to investigate the spin-Seebeck effect in reduced dimensions [15]. A deeper understanding of how spins and phonons couple thermodynamically could in turn lead to fundamentally new applications, such as spin-based cooling and magnetically sensitive thermoelectrics. Here, we investigate the thermoelectric properties of Ga0.95Mn0.05As NWs. Combining thermopower and conductance (or resistance) measurements can provide information on carrier density when conventional characterization techniques via the Hall effect and field effect are not possible [16]. We were able to estimate the hole carrier density from thermopower measurements to be £¿cm£¿3 in our NW. In addition, we find a dramatic rise in the resistance and thermopower of the NW below 120£¿K [17¨C19]. The resistance versus temperature measurements point to the role of Mott variable range hopping (VRH) transport with activation energy 62£¿meV at 100£¿K
%U http://www.hindawi.com/journals/jnt/2012/480813/