Abstract
LEDs on Si offer excellent potential of low cost manufacturing for solid state lighting and display, taking advantage of the well-developed IC technologies of silicon. In this paper, we report how the performance of LEDs grown on Si can be improved. Multiple quantum well InGaN LED structure was grown on patterned silicon substrates and circular LEDs 160 µm in radius were processed. Fabricated LEDs were then transferred to an electroplated copper substrate with a reflective mirror inserted by a double-flip transfer process, to improve the light extraction efficiency and heat dissipation. The light output power of LEDs on copper increased by ~80% after the transfer. The operating current before the onset of light output power saturation also increased by 25% because of the good thermal conductivity of copper. The light output power of packaged LEDs on copper was 6.5 mW under 20 mA current injection and as high as 14 mW driven at 55 mA.
Highlights
Compared with sapphire substrates that are widely used for GaN-based light-emitting diodes (LEDs) growth, Si substrates allow for much lower manufacturing cost, especially if large-area (6- to 12-inch) substrates are adopted, and advantage of IC-like processing are taken for the low- and midend blue, green and white LED markets
We report how the performance of LEDs grown on Si can be improved
Multiple quantum well InGaN LED structure was grown on patterned silicon substrates and circular LEDs 160 μm in radius were processed
Summary
Compared with sapphire substrates that are widely used for GaN-based LED growth, Si substrates allow for much lower manufacturing cost, especially if large-area (6- to 12-inch) substrates are adopted, and advantage of IC-like processing are taken for the low- and midend blue, green and white LED markets. Patterned Si substrates have been used to facilitate small area growth and relieving the stress in the discontinuous GaN film [4] Another major drawback of using Si as substrate is that the light extraction efficiency of LEDs suffers from the light-absorbing property of Si. Almost half of the light emitted downward from the active region is absorbed by the substrate [5], resulting in low external quantum efficiency. It is even more challenging to grow a crack-free LED and DBR with high reflectivity due to the stringent requirements on the epitaxial growth imposed by the relatively large lattice and thermal mismatch. Such long growth time would be highly uneconomical for commercialization even achievable technologically. Copper substrate can significantly improve the heat dissipation of the LEDs, enabling large-area and high power applications of LEDs
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