Novel Thin-Film Resonant-Cavity Light-Emitting Diode Array with Graphene-Based Transparent Conductive Layer and Its Applications in Visible Light Communications (Ii)

In the past year, we have completed the epitaxial growth of InGaN light-emitting diodes (InGaN LEDs) with asymmetric barrier layer (ABL). As a result of the stronger carrier localization, these LEDs exhibit improved performance over conventional LEDs at low current injection levels. In addition, better uniformity of carrier distribution in ABL-containing multiple quantum wells is responsible for the improved roll-off behavior in the light intensity–current characteristics of proposed LEDs operating at high current levels. Otherwise, a 150 Mbit/s visible light communication system based upon an on-off keying modulation scheme and capable of transmitting real-time TV signals over a moderate distance (~1 m) in free space is realized through white InGaN LEDs grown with ABL. In addition to being used as white-light sources, another interesting application based upon resonant-cavity light-emitting diodes (RCLEDs) is to establish an indoor optical wireless link, in which the modulated light signal is directly generated from the LEDs. Compared with conventional LEDs, these RCLEDs with highly directional emission and enhanced modulation bandwidth are considerably suitable for the use in line of sight visible light communications to alleviate the effect of multipath induced intersymbol interference. To improve the performance of visible light communications, an angle-diversity receiver consists of an optical lens and a PIN photodiode array will be used to collect the optical signals. As for the optical transmitters, thin-film RCLED array fabricated by the chemical electrodeposition and laser lift-off technology is considered to be satisfied for that. With the use of the digital predistortion technique, advanced modulation schemes (e.g., quadrature amplitude modulation) or OFDM-based systems, the proposed optical links will have the potential to enable data to be transmitted at a rate exceeding 500 Mbit/s. To meet the demands for the future of consumer electronics, novel transparent conductive materials – graphene will be introduced to RCLED arrays to facilitate uniform current injection to each pixel and to suppress the current crowding effect at high currents. In the experiment, the Au doping process will be performed to reduce the sheet resistance (＜ 50 Ω/square) of graphene-based films (transmittance ＞ 80%) grown by chemical vapor deposition. This can further help improve the output performance of the thin-film RCLED arrays.

Project ID:PB10507-2951
External Project ID:MOST105-2221-E182-026