Defects and Dopants in Silicon Nanowires Produced by Metal-Assisted Chemical Etching

Abstract

The current status of the investigation of defects in silicon nanowires and at the interface between Si and its oxide in 1D nanostructures is reviewed and discussed. The paper concentrates on nanowires produced by metal assisted chemical etching. The role of defects at the interface between the semiconductor and its oxide and of hydrogen in passivating donor atoms is addressed. © The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. Several architectures for ultra-scaled devices targeting classical and quantum information processing, chemical sensing, and energy harvesting and production rely on silicon and germanium nanowires (SiNWs, GeNWs). [1][2][3][4][5][6][7] Despite the efforts in the preparation and characterization of these nanostructures, some fundamental issues remain relatively unexplored. In particular the investigation of defects in 1D nanostructures at the interface between the semiconductor and its oxide or other semiconductors or oxides in core-shell structures represents an important challenge, as the NW diameter reduces and the surface-to-volume ratio increases. 8,9 NWs represent also an interesting system to investigate more fundamental issues such as, for example, Mott transition, spin relaxation mechanisms and scattering processes. In this paper we will review the current experimental data and understanding of the n-type doping of silicon nanowires produced by Metal-assisted Chemical Etching (MACE). The main results concerning the investigation of defects in SiNWs are related to the observation of defects at the Si/SiO 2 interface and in the SiO 2 10-16 and to donors. 12,13,16,17 The role of hydrogen and defects at the interface between the semiconductor and its oxide in the donor de-activation mechanisms will be discussed. Data on SiNWs with diameters larger than 20 nm will be reported therefore excluding discussion of dielectric mismatch and quantum confinement effects. ExperimentalNanowires fabrication.-SiNWs were prepared according to the procedure described by Zhang et al. 18 Either highly resistive (ρ > 5000 cm) silicon (100) wafers or silicon (100) p-type wafers (ρ = 8-12 cm) with a 10 μm thick epilayer on top, n-type (phosphorus doped) with dopant concentration of N D = 1 × 10 17 cm −3 have been used (with the exception of the sample for ToF-SIMS investigation, which was characterized by an epilayer thickness of 5 μm and a P concentration of N D = 1 × 10 19 cm −3 ). Samples having an area of 2 × 2 cm 2 were cleaned with a piranha solution (H 2 SO 4 /H 2 O 2 3:1 v/v) for 10 min at room temperature to entirely remove organics. Wafers were then rinsed with water, etched with a 4...

Probing two-level systems with electron spin inversion recovery of defects at the Si/SiO2 interface

“…For sample B, the seed metal consisted of Ag nanoparticles (NPs), deposited by electroless deposition, as explained in Ref. [18] where also details of the etching process are reported. At the end of the MACE process, the metal was removed from the Si nanowires.…”

“…Both samples were annealed in vacuum for 15 min at 550 • C to induce depassivation of surface defects from the naturally hydrogen-passivated state formed during the MACE process. Details of the depassivation process have been reported elsewhere [18]. The samples were, then, characterized by continuous-wave and pulsed electron paramagnetic resonance (Bruker Elexsys E580 system, X band).…”

“…The samples were, then, characterized by continuous-wave and pulsed electron paramagnetic resonance (Bruker Elexsys E580 system, X band). After the depassivation treatment, the typical electron paramagnetic resonance signal of DB defects at the interface, the so-called P b defects, was observed to increase [18]. Inversion recovery experiments with the magnetic field H [001] were performed in the temperature range of 4-300 K to obtain information on the relaxation rate.…”

“…We show that S z (t ) approaches thermal equilibrium in a highly nonexponential fashion, leading to a wealth of information on the spatial distribution and energetics of TLSs nearby the DB spin. The signal intensity is measurable thanks to nanostructuring of the interface into nanowires (NWs), instead of a flat surface, greatly increasing the surface-to-volume ratio [18].…”

Probing two-level systems with electron spin inversion recovery of defects at the Si/SiO$_2$ interface

“…The signal intensity is measurable thanks to a nanostructuring of the interface into nanowires, instead of a flat surface, greatly increasing the surface-to-volume ratio. [14,15] It is in fact well known that DBs can act as a probe of TLSs because their spin relaxation rate 1/T 1 is strongly dominated by TLS dynamics, even at higher temperatures [16,17]. However, previous experiments [17] were unable to interpret the long time non-exponential decay.…”