nanomaterials Article Fermi-Level Tuning of G-Doped Layers Avto Tavkhelidze 1, *, Amiran Bibilashvili 2 , Larissa Jangidze 1,2 and Nima E. Gorji 3   Citation: Tavkhelidze, A.; Bibilashvili, A.; Jangidze, L.; Gorji, N.E. Fermi-Level Tuning of G-Doped Layers. Nanomaterials 2021, 11, 505. https://doi.org/10.3390/nano 11020505 Academic Editor: Filippo Giannazzo Received: 25 January 2021 Accepted: 15 February 2021 Published: 17 February 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Center of Nanotechnology for Renewable Energy, Ilia State University, Cholokashvili Ave. 3-5, Tbilisi, GA 0162, USA; larisajangidze@gmail.com 2 Institute of Micro and Nano Electronics, Chavchavadze Ave. 13, Tbilisi, GA 0179, USA; amiran.bibilashvili@tsu.ge 3 School of Physical Sciences, Dublin City University, Dublin 9, Ireland; nima.gorji@dcu.ie * Correspondence: avtotav@gmail.com Abstract: Recently, geometry-induced quantum effects were observed in periodic nanostructures. Nanograting (NG) geometry significantly affects the electronic, magnetic, and optical properties of semiconductor layers. Silicon NG layers exhibit geometry-induced doping. In this study, G-doped junctions were fabricated and characterized and the Fermi-level tuning of the G-doped layers by changing the NG depth was investigated. Samples with various indent depths were fabricated using laser interference lithography and a consecutive series of reactive ion etching. Four adjacent areas with NG depths of 10, 20, 30, and 40 nm were prepared on the same chip. A Kelvin probe was used to map the work function and determine the Fermi level of the samples. The G-doping-induced Fermi-level increase was recorded for eight sample sets cut separately from p-, n-, p + -, and n + -type silicon substrates. The maximum increase in the Fermi level was observed at a10 nm depth, and this decreased with increasing indent depth in the p- and n-type substrates. Particularly, this reduction was more pronounced in the p-type substrates. However, the Fermi-level increase in the n + - and p + -type substrates was negligible. The obtained results are explained using the G-doping theory and G-doped layer formation mechanism introduced in previous works. Keywords: nanostructuring; semiconductor; doping 1. Introduction The latest developments in nanotechnology have allowed the fabrication of low- dimensional periodic nanostructures [1–3], including nanogratings (NGs). Imposed peri- odic nanostructures such as NG layers are known to significantly affect the electronic [4,5], thermoelectric [6,7], optical [8,9], electron emission [10,11], and magnetic [12,13] properties of semiconductors when the NG depth becomes comparable to the de Broglie wavelength. This can be attributed to the special boundary conditions enforced by the NG on the wave function. This is because they forbid some quantum states [14], thus reducing their density. Figure 1 shows an NG layer fabricated on a semiconductor wafer surface. Figure 1. Nanograting layer on a substrate surface and the induced G-doped layer. In the proximity of the NG within a layer of thickness d, the density of the quantum states (DOS) reduces. The boundary conditions enforced by the NG layer influence only the wave functions of electrons that are in close proximity to the surface. In contrast, electrons Nanomaterials 2021, 11, 505. https://doi.org/10.3390/nano11020505 https://www.mdpi.com/journal/nanomaterials