Physicists from National Tsing-Hua University in Hsinchu,Taiwan have created light-emitting diodes (LEDs) at nanoscale dimensions that release light across the visible spectrum. Although the small full-color LEDs are not produced for commercial purposes, they can be used in sub-wavelength photolithography and high-resolution microscopy.
The nano-LEDs have a special design that comprises 40-nm-thick nanodisks placed between two nanorod layers forming a nanodisk-in-nanorod arrangement. The nanodisks are fabricated from a semiconducting compound indium gallium nitride (InGaN), which is used in solar cells and LEDs and the nanorods are fabricated from gallium nitride (GaN).
A single nanodisk-nanorod LED viewed with a field-emission scanning electron microscope
The researchers mentioned that full-color LEDs can be obtained by eliminating large lattice strains, which hamper emissions of long wavelength. The InGaN/GaN nanorod system solves this problem by virtue of strain relaxation in the nanostructure design.
The researchers estimate that these full-color LEDs can be utilized to image surfaces at high resolutions and can be used to reconstruct object’s ultra-small sub-wavelength features. These high-resolution imaging methods can be implemented only by rising above the diffraction limit which is possible in techniques using evanescent waves and near-field optics.
Nano-LEDs come useful in scanning near-field optical microscopy (SNOM) where a compact and versatile light source is required that can function well on these probes that retrieve and generate evanescent waves. A nano-LED has been designed with a full-color range for the first time.
The researchers verified the use of nanodisk-in-nanorod LEDs for subwavelength photolithography. During their study, researchers focused a light source to generate a pattern on a light-sensitive substance. They expect to get better spatial control for subwavelength photolithography by using nano-LEDs on probe tips of SNOM.