Within optogenetics there is a need for compact light sources that are capable of delivering light with excellent spatial, temporal, and spectral resolution to deep brain structures. Here, we demonstrate a custom GaN-based LED probe for such applications and the electrical, optical, and thermal properties are analyzed. The output power density and emission spectrum were found to be suitable for stimulating channelrhodopsin-2, one of the most common light-sensitive proteins currently used in optogenetics. The LED device produced high light intensities, far in excess of those required to stimulate the light-sensitive proteins within the neurons. Thermal performance was also investigated, illustrating that a broad range of operating regimes in pulsed mode are accessible while keeping a minimum increase in temperature for the brain (0.5°C). This type of custom device represents a significant step forward for the optogenetics community, allowing multiple bright excitation sites along the length of a minimally invasive neural probe.

The fabrication of gallium-nitride (GaN)-based light-emitting diode (LED) arrays by a direct writing technique, itself using micron-sized LEDs (micro-LEDs), is reported. CMOSdriven ultraviolet GaN-based micro-LED arrays are used to pattern photoresist layers with feature sizes as small as 500 nm. Checkerboard-type square LED array devices are then fabricated using such photoresist patterns based on either single pixel or multipixel direct writing, and implemented as part of a completely mask-less process flow. These exemplar arrays are composed of either 450-nm-emitting 199 × 199 µm 2 pixels on a 200-µm pitch or 520-nm-emitting 21 × 18 µm 2 pixels on a 23-µm pitch. Fill factors of 99% and 71.5% are achieved with optical output power densities per pixel of 5 and 20 W/cm 2 at 90-and 6-mA dc-injected currents, respectively.Index Terms-Gallium nitride, micro light-emitting diodes (micro-LEDs), nanolithography, semiconductor device manufacture.

We report on an approach to ultraviolet (UV) photolithography and direct writing where both the exposure pattern and dose are determined by a complementary metal oxide semiconductor (CMOS) controlled micro-pixellated light emitting diode array. The 370 nm UV light from a demonstrator 8 x 8 gallium nitride micro-pixel LED is projected onto photoresist covered substrates using two back-to-back microscope objectives, allowing controlled demagnification. In the present setup, the system is capable of delivering up to 8.8 W/cm2 per imaged pixel in circular spots of diameter approximately 8 microm. We show example structures written in positive as well as in negative photoresist.

Silver nanoparticle ink has been inkjet-printed onto inorganic GaN-based microstructured light emitting diodes to form narrow conductive tracks with a width down to ~30μm and a resistivity value approximating to that of a conventional sputtered metal (Ti/Au) track. These silver tracks serve as "active" electrodes with comparable performance to the deposited metal tracks, demonstrating a new, simple and cost-effective route for the electrode fabrication of GaN based LED devices.

We report on a new fabrication approach to create individually-addressable InGaN-based nanoscale-LEDs. It is based on the creation by LEEBI of a spatially confined sub-micron-size charge injection path within the p-GaN of an LED structure