Axial p–n-junctions in nanowires

Abstract

The charge distribution and potential profile of p-n-junctions in thin semiconductor nanowires (NWs) were analyzed. The characteristics of screening in one-dimensional systems result in a specific profile with large electric field at the boundary between the n- and p- regions, and long tails with a logarithmic drop in the potential and charge density. As a result of these tails, the junction properties depend sensitively on the geometry of external contacts and its capacity has an anomalously large value and frequency dispersion. In the presence of an external voltage, electrons and holes in the NWs can not be described by constant quasi-Fermi levels, due to small values of the average electric field, mobility, and lifetime of carriers. Thus, instead of the classical Sah-Noice-Shockley theory, the junction current-voltage characteristic was described by an alternative theory suitable for fast generation-recombination and slow diffusion-drift processes. For the non-uniform electric field in the junction, this theory predicts the forward branch of the characteristic to have a non-ideality factor η several times larger than the values 1 < η < 2 from classical theory. Such values of η have been experimentally observed by a number of researchers, as well as in the present work.

Interplay of Surface Recombination and Diode Geometry for the Performance of Axial p–i–n Nanowire Solar Cells

“…In addition to the evaluation of dopant and electrostatic profiles, the photovoltaic (PV) performance of NW axial p–i–n junctions has been evaluated theoretically − as well as in devices composed of single NWs and large-area NW arrays. In devices, it has been shown that a reduction in surface recombination results in significantly improved performance, boosting both photocurrent and photovoltage. ,,,,, Though recombination may place an upper bound on device performance, it is not the sole determinant.…”