Nanoscale imaging of dopant incorporation in n-type and p-type GaN nanowires by scanning spreading resistance microscopy

The realization of practical semiconductor nanowire optoelectronic devices requires controlling their electrical transport properties, which are affected by their large surface/volume ratio value and potentially inhomogeneous electrical dopant distribution. In this article, the local carrier density in Si-doped and Mg-doped GaN nanowires grown catalyst-free by molecular beam epitaxy was quantitatively measured using scanning spreading resistance microscopy. A conductive shell surrounding a more resistive core was observed in Mg-doped, p-type GaN nanowires, balancing the formation of a depleted layer associated with sidewall surface states. The formation of this conductive layer is assigned to the peripheral accumulation of Mg dopants up to values in the 1020 /cm3 range, as determined by quantitative energy dispersive x ray spectroscopy measurements. By contrast, Si-doped n-type GaN nanowires exhibit a resistive shell, consistent with the formation of a depleted layer, and a conductive core exhibiting a decreasing resistivity for increasing Si doping level.