InGaN/GaN nanoLED arrays for bioimaging applications

In recent years, gallium nitride-based light-emitting diodes (GaN LEDs) have been continuously developed and employed in not only solid state lighting but also high-brightness display and optical sensor applications. By integrating them with CMOS control electronics, matrix-addressed and individually controlled blue GaN microLED arrays could be realized with a display luminance of 106 cd/m2 (12 W/cm2), which is a factor of 103 higher than normal commercial displays [1]. Although those optoelectronic devices exhibited promising results and could subsequently be used for illumination sources and manipulation tools in the life sciences, their spatial resolution was still low, which resulted from the LED dimensions with pixel and pitch sizes of 80 × 80 μm2 and 100 μm, respectively. For biologists, however, the imaging at sub-micron resolution is a prerequisite to gain insights of live-cell dynamics and nanostructures at the single-molecule level (e.g., for intracellular fluorescent proteins and activity-dependent plasticity of axon morphology). Therefore, sub-micron or even super-resolution microscopy using compact light sources is urgently needed and would lead to a huge impact on life science research in general. [2]. In this work, InGaN/GaN nanoLED arrays had been designed and fabricated to be used as a nanoillumination source into live-cell imaging inside an on-chip microscope. As the LED pixel dimensions had been scaled down to the sub-micrometer range, the relationship between the nanoscale size and performance of a LED has been investigated, involving extensive optical and electrical simulations. For quick but reliable opto-electrical measurements of nanoLEDs, nanoneedle probing tips inside a scanning electron microscope were utilized (Fig. 1(a)). Hence, I-V and electroluminescence characteristics of small light sources with dimensions of < 1 µm could be extracted (Figs. 1(b), 1(c)). Moreover, the very challenging 3D processing of these high-aspect-ratio top-down nanoLED arrays had been tackled to create nanoLED-based optoelectronic nanodevices. Technological details will also be presented. References: J. Herrnsdorf et al., Active-matrix GaN micro light-emitting diode display with unprecedented brightness. IEEE Transactions on Electron Devices, 62(6), 1918-1925 (2015). F. Balzarotti et al., Nanometer resolution imaging and tracking of fluorescent molecules with minimal photon fluxes. Science, 355(6325), 606-612 (2017)