Micro-transfer printing (μTP) has been widely used to integrate photonic components, such as lasers, modulators, photodetectors, micro-LEDs, on Si photonic platforms. There is a push toward the μTP of optical components in photonics packaging as it enables wafer-scale integration with high alignment accuracy. We demonstrate for the first time the μTP of thick optical components, such as micro-lenses, in the range of 250 to 1000 μm thickness. We explore the reliability of bonding such components using an ultraviolet (UV) curable epoxy and compare them with the current state of the art. The results show that the average shear strength of lenses bonded with InterVia is 19 MPa which is higher than currently used optical epoxies. Also, μTP process has no effect on the surface roughness and microstructure of lenses. Using our approach, we demonstrate how thick silicon and fused silica lenses can be integrated into photonic integrated circuits (PICs) using a tether-free process that is highly scalable and robust.
In this work, the effect of introducing a photonic crystal network of silicon nitride (SiN) micro-domes on the backside of silver coated gallium nitride (GaN) based light emitting diodes (LEDs) was studied. First, sapphire side of the top emitting LEDs, which is the bottom surface of the LEDs, is coated with silver (Ag). Light emitted towards the sapphire substrate is reflected upwards to the top surface and the amount of light extracted from the LED is expected to increase. In an alternative approach, SiN micro-domes forming a two dimensional photonic crystal, 2 μm in diameter and 80 nm in height in average, are deposited on the light emitting surface of the device with a period of 2 μm. Coating the backside with Ag has increased the efficiency of a top emitting LED by 11%. By introducing the SiN photonic crystal onto the Ag backside coated sample, total internal reflection is reduced via scattering and the amount of light emitted has been increased by 30% at 5·104 mA/cm2. Integration of SiN micro-domes with Ag coating has significantly impacted light extraction which has been shown to increase the efficiency of GaN based LEDs. Fabrication process and the results are discussed in detail.
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