Light emission from silicon containing tin nanocrystals

Nanocrystals of diamond-structured tin (alpha-Sn) are very interesting due to their potential use as light emitters and their chemical compatibility with silicon. Here we present our studies on tin nanocrystals embedded in... [ view full abstract ]

Nanocrystals of diamond-structured tin (alpha-Sn) are very interesting
due to their potential use as light emitters and their chemical
compatibility with silicon. Here we present our studies on tin
nanocrystals embedded in silicon. Initially, a layer of tin-rich
silicon was grown by molecular beam epitaxy on a silicon substrate and
covered by a capping layer of silicon. A subsequent heat treatment at
various temperatures, ranging from 650 to 900 degrees, formed the
nanocrystals embedded in silicon by segregation of the tin.

Time-resolved photoluminescence spectroscopy revealed that the samples
emit light in a broad spectrum around 0.8 eV and that the strength of
light emission is particularly strong for one of the samples heat
treated at 725 degrees. In order to investigate the reasons for this
observation, a number of structural characterization techniques were
employed. First, scanning transmission electron microscopy showed that
the nanocrystal diameters were distributed around a mean diameter of
approximately 3 nm - rather independent of the temperature of the heat
treatment. Next, Rutherford backscattering spectrometry showed, after
comparing random and channeling directions, that the sample heat
treated at 725 degrees had its tin atoms placed most coherent with the
surrounding silicon lattice. This suggested that the nanocrystals
consist of tin in the alpha phase in the sample emitting most light;
however, it could not be determined with certainty that no silicon was
included in the nanocrystals. For this reason, the samples have also
been studied by atom probe tomography, which preliminarily has shown
that the nanocrystals are indeed made from pure tin.

We conclude that the sample showing the strongest light emission is
the sample with the highest crystalline quality of alpha-tin
nanocrystals. It is too early to claim that the tin nanocrystals are
the direct source of light emission, but they seem to play a positive
role. For more information, see Roesgaard, et al., AIP Advances 5,
077114 (2015)].