(Invited) Fabrication and Characterization of B- or P- Doped Silicon Nanoparticles Embedded in SiOxNy Transparent Matrix
Authors: Ferblantier Gérald , Ehrhardt Fabien , Le Gall Yann , Muller Dominique , Mathiot Daniel 
Published: May 2020

Silicon nanocrystals (Si-Ncs)-based devices are some of the most studied nanomaterials and could be of great interest in many fields such as electronics1, optical sensing2, photovoltaics3 and biomedicine4. First of all, it is important to control their size, shape and aggregation which are parameters related to their potential applications. In our case, these Si-Ncs are embedded in an insulating dielectric matrix of SiOxNy, resulting in a composite material with a tunable effective bandgap. Doping Si-Ncs can enlarge their applicability by modifying their electrical properties5, the effective bandgap5, the light absorption range and the nanoparticles photoluminescence.
In this study, we used a magnetron sputtering deposition system to deposit silicon rich silicon oxynitride (SiOxNy) thin films. Then, n- and p-type dopants such as boron, arsenic and phosphorus were introduced in the thin films using ion implantation which was carried out at different doses and accelerating energies5. Thanks to a thermal treatment at high temperature, silicon atoms diffuse and nucleate to form silicon nanostructures with size varying between 1.5 nm and several dozen nanometers. This step is necessary for the phase separation leading to the nanoparticles nucleation.
Atom probe tomography (APT) and energy dispersive X-ray mapping in scanning TEM mode, coupled with spectrum imaging on silicon plasmon, were performed to localize the dopant impurities versus the Si-Ncs. The results have showed that n-type (P and As) dopants were energetically favored to be placed into the Si-Ncs core, whereas p-type dopants are preferentially located at the Si-NCs/SiOxNy interface.
The effect of composition and post-deposition annealing temperature on the Si-Ncs light-emitting properties was investigated by the examination of photoluminescence (PL) evolution. The dopants distribution profiles within the host matrix were determined by Rutherford Backscattering Spectroscopy (RBS). EFTEM combined with X Rays mapping analysis have exhibited that the incorporation of arsenic at a high doping level (dose of 5x 1016 As/cm2) leads to an increase of the Si-Ncs size by a factor around 4, precisely from 4 nm to more than 20 nm (Figure 1). On the other hand, the EFTEM-X Rays analysis was unable to detect boron dopants in the SiOxNy films. At this doping level, it could be possible to observe a localized surface plasmon resonance (LSPR) 7.
For both n- and p-type dopants, the silicon nanoparticles crystalline fraction was found to be much higher than the undoped structures. The dopants facilitate the nucleation and growth of crystalline nanoparticles. This behavior is quite similar to that observed for thin amorphous silicon films. The results have showed that the nanostructures shape have different behaviors depending on the dopants.
Finally Schottky diodes were prepared. The I-V characteristic curves show that the electrical conduction in the -doped structures increases with the dopant doses and we obtained a rectifier behavior. The results have showed that the heavily As-doped silicon structures are limited by the tunnel oxide thickness between the large Si-Ncs. These results are very encouraging when aiming at implementing such nanocomposite materials in photovoltaic solar cells.
References:
1. Rev. 2010, 110, 339-458.
2. Photoenergy 2012, 872576.
3. Photovolt.: Res. Appl. 2001, 9, 12-135.
4. J. Nanomed. 2006, 1, 451.
5. Phys. Lett. 2013, 102, No.013116
6. Appl. Phys. 2013, 114 Issue 3
7. Rev. Lett. 2013, 11, 177402.

Figure 1