Controlled axial and radial Te-doping of GaAs nanowires

Tellurium (Te)-doping of Au-catalyzed GaAs nanowires (NWs) grown by metalorganic vapor phase epitaxy (MOVPE) via the vapor-liquid-solid (VLS) mechanism is presented. Electrical measurements were performed inside a scanning electron microscope by contacting a tungsten nanoprobe to the Au end of individual NWs grown on a heavily n-type GaAs substrate. Rectifying current-voltage (I-V) characteristics are observed due to the formation of a junction at the Au nanoparticle (NP)/NW interface. The electron concentration n(e) and contact barrier heights, phi(0b), were determined from the analyses of these characteristics. As expected, phi(0b) increased (from 0.63 +/- 0.03 eV to 0.71 +/- 0.02 eV) with decreasing Te-precursor flow rate, corresponding to a decrease in n(e) from (961) x 10 17 cm(-3) to (1.5 +/- 0.5) x 10(17) cm(-3). Meanwhile, undoped NWs had space-charge-limited characteristics. There was a large influence of the residual gallium (Ga) in the NP, on barrier properties, controlled by the group V precursor flow (on or off) during the cooling of the NW sample at the end of the growth process. With the group V flow off during cooling, a decrease in phi(0b) from 0.79 +/- 0.04 eV to 0.63 +/- 0.03 eV is observed consistent with a higher Ga alloy concentration in the NP, confirmed by energy dispersive spectroscopy measurements. We also demonstrate the fabrication of core/shell, undoped/Te-doped, GaAs NWs with very high Te doping (similar to 10(19) cm(-3)). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4751988]