Matrix role in Ge nanoclusters embedded in Si3N4 or SiO2

Abstract

Ge nanoclusters (NCs), synthesized by ion implantation and annealing up to 900 °C, result small (∼2 nm) and amorphous in Si3N4, crystalline and much larger in SiO2. The NCs ripening and crystallization kinetics in Si3N4 is retarded by larger interfacial energy and lower diffusivity of Ge in comparison to SiO2. Ge NCs absorb light more efficiently when embedded in Si3N4 than in SiO2. A significant effect of the barrier height on absorption was evidenced, in agreement with effective mass theory predictions. The smaller bandgap of Ge NCs embedded in Si3N4 and their closeness is promising features for light harvesting applications.

Light harvesting with Ge quantum dots embedded in SiO2 or Si3N4

“…This point is further confirmed by previous observation of stoichiometric Si 3 N 4 and SiO 2 matrices implanted with Ge. 18 In that case, the lower diffusivity of Ge in Si 3 N 4 (below 7 Â 10 À17 cm 2 /s at 850 C) compared with SiO 2 (of the order of 10 À13 cm 2 /s at 800 C 28 ) retarded the QD ripening in Si 3 N 4 and led to the formation of a narrow size distribution ($2 nm) of Ge QDs in Si 3 N 4 against a more sparse array of larger QDs (size $ 3 _ 24 nm) in SiO 2 . In this paper, a similar behavior occurs for PECVD SiGeO and SiGeN alloys, indicating a clear role of the embedding matrix in the nucleation and growth of Ge QDs.…”

“…19 However, contrasting results appear in the literature for the growth kinetics of QDs in SiO 2 20 On the contrary, stoichiometric Si 3 N 4 films implanted with Ge showed retarded QD ripening and crystallization kinetics with respect to Ge QDs in SiO 2 implanted with the same Ge dose. 18 A significant role of the embedding matrix was also found for the optical bandgap of these systems, with Ge QDs in Si 3 N 4 absorbing light more efficiently than in SiO 2 . 18 This effect, together with the lower tunneling barrier height offered by Si 3 N 4 , could potentially open a route toward the fabrication of efficient photodetectors and solar cells.…”

“…18 A significant role of the embedding matrix was also found for the optical bandgap of these systems, with Ge QDs in Si 3 N 4 absorbing light more efficiently than in SiO 2 . 18 This effect, together with the lower tunneling barrier height offered by Si 3 N 4 , could potentially open a route toward the fabrication of efficient photodetectors and solar cells.…”

“…Other effects have been demonstrated to have a strong role in the light absorption/emission process such as: mid-gap states and defects at the interface with the matrix, [12][13][14] crystallinity (amorphous (a-) or crystalline (c-)) of QDs, 15 the shape of the QDs and their size distribution, 16,17 as well as the nature of the surrounding matrix. 18 However, one of the main problems with quantum dots embedded in dielectrics is the poor extraction of photo-generated carriers. Compared with silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ) matrix can be a promising new host matrix for QDs.…”

The role of the interface in germanium quantum dots: when not only size matters for quantum confinement effects

“…Several studies demonstrated how the optical properties of Si nanostructures can be varied by solely managing the nanostructure shape, 15 the QD crystalline structure, 16,17 or the potential barriers surrounding the QD. [18][19][20] Even though a multilayerednanostructure approach and an appropriate surface passivation could allow an efficient control of QCE via size-tuning only, 13 the optical properties of confined systems can be † SC contributed to sample processing, characterization, data analysis and interpretation, and drafted the manuscript. AMM performed STEM and EELS analysis, together with data interpretation.…”