Towards MEMS-tuneable nanowire lasers?
The researchers bridged CdS nanowires several micrometre long (and from 100 to 700nm in diameter) across SiO2 pads on separate SOI substrates and observed their electroluminescence under optical excitation (at 355nm) while varying the pads’ spacing distance using a micromechanical stage.
state. The NW is suspended in between two
oxidized Si pads (in blue). The enlarged excitation
laser spot homogeneously illuminating the NW is
visualized in purple.
In their experiments, the researchers distinguished two different strain-related effects. First, the CdS nanowire elongation caused by a uniaxial stress gave rise to a redshift of the individual resonator modes. Secondly, the bandgap reduction in strained parts of the NW lead to a broadening and a redshift of the gain spectrum and thus the lasing mode envelope.
Although only offering a proof of principle, the researchers hint that such dynamical strain-tuning in semiconductor nanowires could be extended to electrically driven devices such as LEDs, possibly by combining NW LEDs with a MEMS structure for dynamic strain control (and spectra tuning).
They anticipate that such a combination could yield micro spectroscopic devices tuneable over a ±10nm range (corresponding to strain values of up to ±3 or 4%).
University of Jena – www.uni-jena.de
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