Nanoscale physics

Double injection in nanowire radial p-i-n diodes
Borblik V.L.
Department of Electric and Galvanomagnetic Properties of Semiconductors, V.Lashkaryov Institute of Semiconductor Physics of the NAS of Ukraine. Prospect Nauki, 41, Kyiv-03680, Ukraine. 
E-mail: borblik@isp.kiev.ua
The most of semiconductor nanowire devices contain radial p-n or p-i-n junctions and use transverse transport through them. Due to cylindrical symmetry of such the structures, their electronic properties acquire a number of peculiarities in comparison with analogous planar devices. In particular, distribution of the nonequlibrium carriers injected into base layer of the radial p-n junction diode decays with different rate depending on the injection direction - from the nanowire center to periphery or vice versa [1]. The reason is overlaying of specific concentration falling with radial coordinate related to cylindrical geometry of the structure onto its falling due to recombination. This circumstance results in, respectively, increasing or decreasing the diode saturation current compared with analogous planar diode. And electric field in i-layer of radial p-i-n diode proves to be inhomogeneous primordially, decaying from the nanowire center [2].
The radial p-i-n diodes contain (in the frame of single device) both above mentioned injection directions. Therefore it is of interest to consider their transport properties in whole.
It is shown in the work that cylindrical geometry of the structure gives rise to specific asymmetry of concentration distribution for the carriers injected to the i-layer which superimposes on the asymmetry due to inequality of carriers’ mobilities. This specific asymmetry rises with bringing the i-layer nearer to the nanowire center. Together with that, decrease of the current density in  “long” p-i-n diode and its increase in “short” p-i-n diode take place (at given forward voltage). And variation of radial thickness of the i-layer demonstrates maximums of the current density at its thickness close to the bipolar diffusion length. These maximums are proving to be larger in the diode with the core of p-type than in the diode with the core of n-type.

1.	Borblik V.L. Effect of circular p-n junction curvature on the diode current density // J. Electron. Mater.-2016.-45.-P. 4117-4121.
2.	Borblik V.L. Electrostatics of nanowire radial p–i-n diode // Semicond. Phys. Quantum Electron. & Optoelectron.-2019.-22, N 2.-P. 201-205.