Nanoscale physics

Electrostatics of a nanowire heterostructure radial p-i-n diode
 Borblik V.L.
Department of electrical 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

Semiconductor nanowires are used mostly in the form of multilayer structures in which material and/or doping type change either in radial or axial direction. In particular, nanowires with p-n junctions have found broad application as radiation detectors, solar cells, light emitting device and lasers. It has been shown that the radial core-shell nanowires have certain adventures compared with axial ones [1].
In many cases, p-i–n structures prove to be more effective than simple p-n structures because they extend a region of the built-in electric field. Theoretical analysis [2] has shown that electric field in i-layer of the radial p-i–n diode is inhomogeneous and its maximum value can be both lower and higher in comparison with electric field in equivalent planar p-i–n diode.
However often not homo but hetero p-i–n diodes are used in the applications. Therefore it is of interest to consider electronic properties of the radial heterostructure p-i–n diode. 
In p-i–n structure symmetrical on doped materials (i.e. when p- and n- layers are made of the same semiconductor), entering into p-n junction of the i-layer with larger dielectric constant than that of the doped layers lowers electric field in it, and entering of i-layer with smaller dielectric constant - raises the field. Besides, it is turn out that entering i-layer into p-n junction extends the electric field region not always. At middle doping levels, depletion widths of the p- and n- layers so decrease under entering i-layer that total thickness of the electric field region does not increase practically.
In p-i-n structure asymmetrical on doped materials, two different cases are possible: 1) the core material has narrower gap in comparison with material of the external shell and 2) reverse situation. The second-type structure provides significantly higher built-in electric field in the i-layer than the first-type structure does.
1.	J. D. Christesen, X. Zhang, C. W. Pinion, T. A. Celano, C. J. Flynn, and J. F. Cahoon Design principles for photovoltaic devices based on Si nanowires with axial or radial p-n junctions // Nano Lett. -2012.-12, -P. 6024-6029.
2.	Borblik V.L. Electrostatics of nanowire radial p–i-n diode // Semicond. Phys. Quantum Electron. & Optoelectron.-2019.-22, N 2.-P. 201-205.