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|a Gallium Arsenide nanowires (GaAs NWs) have been grown on GaAs and Silicon (Si) substrates by gold-assisted and using metal-organic chemical vapor deposition (MOCVD) method. The structural properties and electrical conductivity were studied and was found to be strongly dependent on the pre-annealing temperature, growth temperature, growth period and V/III ratio. Pre-annealing process at 600 oC has produced an eutectic point of Au and GaAs substrate and initiated the growth of the NWs. The NWs were uniform in diameter and composition at a growth temperature of 460 oC, growth period of 30 minutes and V/III ratio of 166. Activation energy for the NWs in the temperature range (420 - 480) oC was found to be 58.86 kJ/mol. Energy dispersive X-ray analysis (EDX) indicated the presence of Au, Ga and As. From the field-emission scanning electron microscopy (FE-SEM), the growth of the NWs were at an elevation angle of 90o, 60o, 65o and 35o with respect to the GaAs substrate for (111)B, (311)B, (110) and (100) orientations respectively. The NWs grew vertically, randomly and horizontally on the Si(100) substrate when there was no pre-annealing process, pre-annealing process at a temperature of 600 oC for 10 minutes and an extended pre-annealing process at 450 oC for 7 minutes respectively. Highresolution transmission electron microscope (HRTEM) micrograph showed the NWs that grew on the GaAs(100) substrate has less structural defects when compared to the GaAs(111)B. The electrical conductivity of the NWs from the measurement of the conductive atomic force microscope (CAFM) showed similar to that of a p-n junction characteristics. The energy gap for the GaAs NW was found to be 1.50 eV.
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