Credit: © 2007 ACS

There is great potential for narrow-gap semiconductor nanocrystals in optoelectronic applications. Typically, such nanocrystals have a bandgap that can be tuned between 0.5 and 1.5 eV, which covers the near-infrared spectral region. However, synthesizing nanocrystals with a bandgap energy below this range has proven to be a challenge.

Now, Maksym Kovalenko and colleagues1 at the Johannes Kepler University in Linz, Austria and the Lawrence Berkeley Laboratory in the US have made SnTe nanocrystals with tunable bandgaps that lie in the mid-infrared, reaching as narrow a gap as 0.38 eV. Using a solution-phase synthesis, they are able to tune the nanoparticle size, which determines the band gap, by varying the growth temperature and concentration of the reagents. With the same process, it is also possible to fabricate the narrow band-gap semiconductors SnS and SnSe in nanocrystalline form.

SnTe nanocrystals are expected to be excellent materials for mid-infrared applications and may be optimal for use in solar cells. Moreover, the surface of the nanocrystals can be modified in order to increase their conductivity, which will improve their potential for these applications even further.