Nanoscale physics

Electrostatics of the nanowire radial p-i-n diode
Borblik V. L.

V. Lashkaryev Institute of Semiconductor Physics of the NAS of Ukraine. Prospect Nauki 41, Kyiv-03680, Ukraine. 
E-mail: borblik@isp.kiev.ua

In the recent time, a great interest of the investigators is attracted to semiconductor nanowires, especially to the multilayer ones whose layers either are doped in different way or form the heterostructure. On the base of such structures, principally new constructions of the core-shell p-n devices are created which use  transverse (radial) transport of the current carriers (radial solar cells, radial photodiodes, radial light emitting devices).
In the same time, such the structures use often not p-n but p-i-n junctions [1,2]. This makes it possible, in particular, to broaden the region of strong electric field in the junction that is additional advantageous in materials with short minority carrier diffusion lengths. Electrostatics of such the structures was not studied so far. 
The calculations carried out show that, in contrast to planar p-i-n diode, the built-in electric field of the nanowire radial p-i-n diode proves to be inhomogeneous. This field is maximal in the section of the i-layer adjoining to the core. When the i-layer (with given thickness) moves away from the nanowire center, degree of the field inhomogeneity decays, and both edge values of the field in the i-layer reach eventually the common magnitude which takes place in analogous planar p-i-n diode. This magnitude can be both higher and lower than maximal field in the nanowire p-i-n diode (depending on doping conditions). Simultaneously, capacitance of the nanowire p-i-n diode can both increase and decrease in value, going in the same time to weak voltage dependence, inherent to planar p-i-n diode.

1. 	Colombo C., Heiβ M., Grätzel M., Fontcuberta i Morral A. Gallium arsenide p-i-n radial structures for photovoltaic applications // Appl. Phys. Lett. -2009.-94, N 17.-P. 173108.
2. 	Yoo J., Dayeh S. A., Tang W., Picraux S. T. Epitaxial growth of radial Si p-i-n junctions for photovoltaic applications // Appl. Phys. Lett. -2013.-102,  N 9. -P. 093113.