RESUMO
The fabrication of complex nanoscale electronics with reduced dimensions poses challenges on novel techniques to accurately determine fundamental electronic parameters. In this article, we present a universal contactless method based on Raman scattering for measuring the mobility and hole concentration independently in GaAs:Zn and Mn ion-implanted GaAs:Zn nanowires, potentially of great interest for spintronics applications. Clear coupled longitudinal optical phonon-plasmon modes were recorded and fitted with a dielectric function, based on the Drude model, which includes contributions from both plasmons and phonons. From the fitting, we extract accurate values of the plasma frequency and plasma damping constant from which we directly calculate the hole density and mobility, respectively. The extracted mobilities were also used as input data for analysis of complementary four-probe transport measurements, where the corresponding hole concentrations could be calculated and found to be in good agreement with those extracted directly from the Raman data. We also investigated the influence of annealing of the GaAs:Zn nanowires on the hole concentration and mobility and found strong indications of thermally activated defects related to a formed crystalline As/oxide shell around the nanowires. The method proposed here is extremely powerful for the characterization of nanoelectronics in general, and nanospintronics in particular for which Hall measurements are difficult to pursue due to problems related to contact formation, as well as to inherent magnetic properties of the devices.
RESUMO
Recent progress in the realization of magnetic GaAs nanowires (NWs) doped with Mn has attracted a lot of attention due to their potential application in spintronics. In this work, we present a detailed Raman investigation of the structural properties of Zn doped GaAs (GaAs:Zn) and Mn-implanted GaAs:Zn (Ga0.96Mn0.04As:Zn) NWs. A significant broadening and redshift of the optical TO and LO phonon modes are observed for these NWs compared to as-grown undoped wires, which is attributed to strain induced by the Zn/Mn doping and to the presence of implantation-related defects. Moreover, the LO phonon modes are strongly damped, which is interpreted in terms of a strong LO phonon-plasmon coupling, induced by the free hole concentration. Moreover, we report on two new interesting Raman phonon modes (191 and 252 cm-1) observed in Mn ion-implanted NWs, which we attribute to Eg (TO) and A1g (LO) vibrational modes in a sheet layer of crystalline arsenic present on the surface of the NWs. This conclusion is supported by fitting the observed Raman shifts for the SO phonon modes to a theoretical dispersion function for a GaAs NW capped with a dielectric shell.