Fabrication and characterization of the substrate-free InGaN-based resonant-cavity light-emitting diodes for plastic optical fiber communications

In this article, the authors report on the realization of substrate-free InGaN-based thin-film resonant-cavity light-emitting diodes (TF-RCLEDs). Experimentally, the sapphire substrate was stripped by using the laser lift-off technique. The λ/4 -thick Ta₂ O₅ /Si O₂ distributed Bragg reflector and the metallic Ag film with mirror reflectivities of 68% and 97% were, respectively, coated onto the top and bottom of the substrate-free LEDs to form a Fabry-Ṕrot cavity. The performances of LEDs are characterized by light output power, external quantum efficiency, emission spectrum, angular-resolved intensity distribution, and dynamic response. As a result, the fabricated TF-RCLEDs exhibit a low operating voltage of 3.34 V at 20 mA, a maximum light output power of 6.3 mW at 140 mA, and an external quantum efficiency of 5.5% at 4 mA. In addition, the TF-RCLEDs show temperature insensitivity as compared to the normal LEDs directly grown on the sapphire substrates. Furthermore, the 50% viewing angle of TF-RCLED is smaller than that of normal LED, i.e., 146° versus 168° at 60 mA. Finally, the eye pattern of the TF-RCLEDs is improved compared to that of the normal LEDs as operated at the data transmission rate of 100 Mbit/s. These results exhibit that the InGaN-based TF-RCLEDs are excellent candidates for the use in short-distance plastic optical fiber communications.