Realization of high efficiency ultrasound-powered micro-LEDs for optogenetics

We present the fabrication, characterization, and demonstration of high-efficiency ultrasound-powered micro-light emitting diodes (mu LED) for use in optogenetic applications. InGaN based blue-emitting LED material wafers grown on a patterned sapphire substrate (PSS) were used to assist in the out-scattering of the light. The turn-on voltage of the LEDs is around 2.5 volts and the electrical ideality factor is 1.2 confirming high radiative recombination efficiency. A power density of more than 50 mW/mm(2) was obtained from a 130 x 300 mu m(2) LED with a mesa of 100 mu m diameter at 3 mA which is much more than is required to excite channelrhodopsin transfected neural cells. A high external quantum efficiency (EQE) of 33% is obtained at 3 mA measured in an integrating sphere. The peak wavelength of the mu LED was measured at 483 nm at different current densities. The mu LEDs are integrated directly onto a rectifier and Piezoelectric Transducer (PZT) harvester to realise a highly efficient ultrasound-powered light delivery unit capable to generate mWs of optical power. The concept was validated by powering the integrated device with ultrasound.