Experimental and theoretical rationalization of the growth mechanism of silicon quantum dots in non-stoichiometric SiN_x: role of chlorine in plasma enhanced chemical vapour deposition

Abstract

Silicon quantum dots (Si-QDs) embedded in an insulator matrix are important from a technological and application point of view. Thus, being able to synthesize them in situ during the matrix growth process is technologically advantageous. The use of SiHCl as the silicon precursor in the plasma enhanced chemical vapour deposition (PECVD) process allows us to obtain Si-QDs without post-thermal annealing. Foremost in this work, is a theoretical rationalization of the mechanism responsible for Si-QD generation in a film including an analysis of the energy released by the extraction of HCl and the insertion of silylene species into the terminal surface bonds. From the results obtained using density functional theory (DFT), we propose an explanation of the mechanism responsible for the formation of Si-QDs in non-stoichiometric SiN starting from chlorinated precursors in a PECVD system. Micrograph images obtained through transmission electron microscopy confirmed the presence of Si-QDs, even in nitrogen-rich (N-rich) samples. The film stoichiometry was controlled by varying the growth parameters, in particular the NH/SiHCl ratio and hydrogen dilution. Experimental and theoretical results together show that using a PECVD system, along with chlorinated precursors it is possible to obtain Si-QDs at a low substrate temperature without annealing treatment. The optical property studies carried out in the present work highlight the prospects of these thin films for down shifting and as an antireflection coating in silicon solar cells.

A High-Performance SiO2/SiN x 1-D Photonic Crystal UV Filter Used for Solar-Blind Photodetectors

“…The silicon and oxygen precursors were SiH 4 (5%) and N 2 O, respectively. For comparison, we choose N 2 [9], [10] and NH 3 [11], [12] as nitrogen precursor, respectively. Initially, the single SiN x and SiO 2 layers were deposited respectively at the reactor to calibrate the growth rate and optical constants about refractive index (n) and extinction coefficient (k).…”

Silicon Compound Nanomaterials: Exploring Emission Mechanisms and Photobiological Applications

“…The hydrogen from the precursor helps to extract the Cl from the thin‐film surface, thus forming an HCl bond. [ 24 ] These reaction changes could be either exothermic or endothermic in nature. On the other hand, the probability that atomic hydrogen breaks the weaker bonds from the thin film, either on the surface or in bulk, is very high.…”

“…The most probable bonds to be broken during the reaction process are SiH, NH, and SiSi. [ 24 ] In this way, the SiH and SiSi breaking bonds help in the formation of reaction centers for growth enhancement of Si NPs and QDs inside the SiNx matrix, whereas dissociation of the NH bond endorses the matrix growth, favoring insertion of the silylene species (exothermic reactions) which can increase the average size of Si NPs and QDs. According to the theoretical calculations obtained in this report, in all cases, the insertion of silylene species on the SiCl and SiH bonds generated crystalline zones in the nitride matrix producing many SiSi bonds.…”

“…According to the theoretical calculations obtained in this report, in all cases, the insertion of silylene species on the SiCl and SiH bonds generated crystalline zones in the nitride matrix producing many SiSi bonds. [ 24 ] Consequently, the exothermic reactions could induce a local heating process inside the matrix, and as a result, the crystallinity of Si QDs is enhanced in the case of the SiN x rich in Si, as evidenced by Figure a,b and the SAED images shown in Figure 11c when compared with Figure 11d–f for SiN x matrix rich in nitrogen. [ 24 ] In all cases, these samples showed visible PL following the QCE, as observed in Figure 11g for the silicon‐rich and nitrogen‐rich matrix, respectively.…”

“…Several investigations related to the structural, optical, and electrical analysis of Si‐based nanomaterials have been explored and discussed in some of our recently published reports. [ 22–29 ] Now, keeping in mind the optical responses offered by Si‐based compound nanomaterials (QDs, SiO x , SiN x , SiC) and the experience gained from our previous studies, we believe that the PL properties could be a linking point to the biological research. Moreover, in this review, the Web of Science database has been used to compile information about the number of literature reports in the area, in general, for bioimaging and optical diagnostics.…”