We present the method for growing GaAs nanowires by MBE without using gold as a catalyst. With careful choice of the growth parameters nanowires with length of several microns and diameters in the range of 20 nm up to 120 nm are obtained. By changing the growth conditions it is also possible to obtain radial and axial heterostructures. In view of using nanowires for photovoltaic applications, we will present the latest developments on the doping mechanisms of GaAs nanowires by MBE. Finally, we show how the fabrication of p-i-n junctions can be used for solar cell applications. © 2012 IEEE.