InGaN-based resonant-cavity light-emitting diodes fabricated with a Ta ₂O₅SiO₂ distributed bragg reflector and metal reflector for visible light communications

The potential of visible light communications based upon phosphor-converted white resonant-cavity light-emitting diodes (RCLEDs) is investigated experimentally. To fabricate a blue InGaN RCLED, a λ4-thick Ta ₂O₅SiO₂ distributed Bragg reflector, along with a metallic Ag layer, were respectively coated onto the top and bottom of normal LEDs to form an optical cavity. As evaluated from the emission spectrum of blue RCLEDs, the discrepancy of the expected cavity length from the measurements suggests that cavity oscillation may mostly occur in the GaN-based epistructures. In addition to the presence of the optical cavity effect, the incorporation of a bottom reflector is useful to increase the light extraction efficiency of the RCLEDs. As a result, these RCLEDs exhibit improved operational characteristics over normal LEDs in terms of light output power, external quantum efficiency, spectral purity, and directionality. With an increase in injection current, the enhancement of the spontaneous emission rate is responsible for the improved quality of eye patterns in blue RCLEDs operating at a transmission rate of 100 Mbit/s and 175 mA. After encapsulating the blue RCLEDs with a phosphor layer, we found that white RCLEDs have the capacity for free-space optical communication with a data rate of 12 Mbit/s.