Ultrafast Carrier Relaxation Dynamics in Quantum Confined Non-Isotropic Silicon Nanostructures Synthesized by an Inductively Coupled Plasma Process

Materials

Simona Boninelli¹  Marta Agati²  Paola Castrucci³  Stefania Pagliara⁴  Sonia Freddi⁴  Stefano Ponzoni⁴  Vincent Le Borgne⁵  MyAli El Khakani⁵  Richard Dolbec⁶ 

[1] CNR IMM-MATIS, Via S. Sofia 64, 95123 Catania, Italy;Dipartimento di Fisica e Astronomia, Università degli Studi di Catania, Via S. Sofia 64, 95123 Catania, Italy;Dipartimento di Fisica, Università degli Studi di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy;I-Lamp and Dipartimento di Matematica e Fisica, Università Cattolica del Sacro Cuore, via dei Musei 41, 25121 Brescia, Italy;Institut National de la Recherche Scientifique, Centre-Énergie, Matériaux et Télécommunications, 1650 Blvd. Lionel-Boulet, Varennes, QC J3X-1S2, Canada;Tekna Plasma Systems Inc., 2935 Industrial Blvd., Sherbrooke, QC J1L 2T9, Canada;

关键词: Si nanostructure;    pump-probe;    quantum-confinement;   

DOI  :  10.3390/ma13194267

来源: DOAJ

【 摘 要 】

To exploit the optoelectronic properties of silicon nanostructures (SiNS) in real devices, it is fundamental to study the ultrafast processes involving the photogenerated charges separation, migration and lifetime after the optical excitation. Ultrafast time-resolved optical measurements provide such information. In the present paper, we report on the relaxation dynamics of photogenerated charge-carriers in ultrafine SiNS synthesized by means of inductively-coupled-plasma process. The carriers’ transient regime was characterized in high fluence regime by using a tunable pump photon energy and a broadband probe pulse with a photon energy ranging from 1.2 eV to 2.8 eV while varying the energy of the pump photons and their polarization. The SiNS consist of Si nanospheres and nanowires (NW) with a crystalline core embedded in a SiO_x outer-shell. The NW inner core presents different typologies: long silicon nanowires (SiNW) characterized by a continuous core (with diameters between 2 nm and 15 nm and up to a few microns long), NW with disconnected fragments of SiNW (each fragment with a length down to a few nanometers), NW with a “chaplet-like” core and NW with core consisting of disconnected spherical Si nanocrystals. Most of these SiNS are asymmetric in shape. Our results reveal a photoabsorption (PA) channel for pump and probe parallel polarizations with a maximum around 2.6 eV, which can be associated to non-isotropic ultra-small SiNS and ascribed either to (i) electron absorption driven by the probe from some intermediate mid-gap states toward some empty state above the bottom of the conduction band or (ii) the Drude-like free-carrier presence induced by the direct-gap transition in the their band structure. Moreover, we pointed up the existence of a broadband and long-living photobleaching (PB) in the 1.2–2.0 eV energy range with a maximum intensity around 1.35 eV which could be associated to some oxygen related defect states present at the Si/SiO_x interface. On the other hand, this wide spectral energy PB can be also due to both silicon oxide band-tail recombination and small Si nanostructure excitonic transition.

【 授权许可】

Unknown