A key requirement for the realization of nanowire (NW) devices is the ability to control axial and radial growth. Despite the extensive literature on this subject there have been relatively few reports of the role of precursor chemistry in the growth on NWs by metalorganic vapor phase epitaxy (MOVPE). Recently we have shown that the choice of Ga precursor can have dramatic effects on the morphology of GaAs NW grown by the vapor-liquid-solid (VLS) mechanism. The vast majority of previous MOVPE works on this topic have employed methyl-alkyl precursors such as trimethylgallium (TMGa). In core shell structures, control over axial vs. radial growth is usually achieved by varying the growth temperature. At low temperatures, lateral growth is inhibited, resulting in enhanced axial growth, while at high temperatures, lateral growth competes with VLS growth, enabling the formation of shell structures. A similar effect can be achieved by changing precursor chemistry by using less stable precursors whose vapor-solid (VS) growth rate is not kinetically inhibited. In this work we show that the use of triethylgallium greatly enhances lateral growth, permitting the formation of core shell heterostructures without changing the growth temperature. TEGa decomposes at lower temperatures than TMGa, resulting in gas diffusion limited growth for planar films at temperature ~80°C lower than TMGa. The formation of NWs by the VLS mechanism requires the kinetic hindrance of vapor solid growth on the substrate surface and nanowire sidewalls. NWs grown with TMGa generally exhibit low tapering/sidewall growth because VS growth is suppressed except at the highest temperatures. The use of TEGa results in increased competition for Ga vapor flux, resulting in the formation of much higher levels of tapering in NWs grown with TEGa alone, due to the much increased lateral growth. This suggests a strategy for growth of core shell homoepitaxial or heteroepitaxial structures by simply changing group III precursors. We have employed this technique to form InAs/GaAs heterostructures using trimethylindium (TMIn) and either TMGa or TEGa. The precursor sequence TMIn followed by TMG results in axial heterostructures with relatively abrupt interfaces as determined by EDS. In contrast under identical growth conditions, the sequence TMIn followed by TEGa results in InAs-core/GaAs-shell structures with little GaAs axial growth. We have also investigated the effects of carbon doping with CBr<sub>4</sub> dopant. Carbon is an excellent p-type dopant for planar growth of GaAs and other III-Vs. We show that the combination of TEGa and CBr<sub>4</sub> is ideal for the formation of p-type GaAs NW shells. In addition the use of diethytellurium is reported as an n-dopant for GaAs NW cores. This combination of precursors enables us to form n-core p-shell structures, which are the building blocks for potential device applications such as NW photovoltaics.