Single InGaN nanodisk light emitting diodes as full-color subwavelength light sources
Click to view
(a) Field-emission scanning electron microscopy (FE-SEM) image of a single InGaN/GaN nanodisk-nanorod LED. (b) Room-temperature characteristics of the nanorod LED shown in (a). Inset shows the schematic diagram of the measured nanorod structure. (c) Optical microscopy images ( objective lens) of the diffraction-limited light emissions from single InGaN/GaN nanodisk-nanorod LEDs under forward bias (injection current: 500 nA), showing violet, blue, cyan, green, and yellow emissions, respectively. The corresponding EL spectra (normalized) show that the emissions from single InGaN nanodisks are monochromatic with narrow spectral widths. (d) EL spectra of a single InGaN/GaN nanodisk-nanorod LED emitting at 475 nm with injection currents from 100 nA to 500 nA [the same diode measured in (b)]. Inset shows the EL intensity exhibits a monotonic increase with increasing current for up to 500 nA, corresponding to a current density of .
Click to view
(a) Polarized EL spectra of a single InGaN/GaN nanodisk-nanorod LED [the same structure shown in Fig. 1(b)] at 500 nA injection current. These spectra were recorded with the emission polarization oriented parallel (black curve) and perpendicular (red curve) to the nanorod axis (the -axis of the wurtzite crystal structure). The measured polarization ratio is as large as −0.85. The insets show the corresponding optical microscopy images under a objective lens. (b) The measured polar plot of the integrated EL intensity as a function of the emission polarization angle.
Click to view
Negative-tone photoresist layers were spin coated on top of the InGaN/GaN nanodisk-nanorod LED structures and exposed by single InGaN nanodisks. The lithographic feature size depends on the EL wavelength, intensity, and exposure time. (a) Large-area FE-SEM image of one example of LED-exposed resist pattern (dark region, after development) with a diameter of about . Dashed lines show the electrodes, while the solid lines show the positions of the nanorod and the metallic contact wires. (b) High-magnification FE-SEM image of a photoresist structure patterned by using a single nanorod LED. The diameter of exposed and developed photoresist pattern is around 850 nm. (c) Plots of integrated EL intensities as functions of injection current for two different nanorod LEDs emitting at 485 nm. The patterning feature size critically depends on the EL intensity under the conditions of fixed wavelength and constant exposure time. By controlling the injection current and monitoring the calibrated EL intensity, we can obtain the desired sizes of the photoresist patterns. In the insets, the achieved subwavelength pattern is around 200 nm in diameter, while the other one is around 700 nm (just above the subwavelength size window). For the case that the EL intensity is below the threshold value, no photoresist patterns can be formed.
Article metrics loading...
Full text loading...