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

To facilitate increased substitution of energy-saving LEDs for conventional lighting sources requires further improvement in light intensity/internal quantum efficiency and alleviating the phenomenon of efficiency droop at high current density. In comparison with conventional InGaN LEDs with the coplanar p- and n-contacts for current injection, thin-film InGaN RCLEDs fabricated with a metal substrate are useful for LED luminaires due to their attractive features in terms of enhanced light intensity, better heat dissipation and directionality. In addition, the issues associated with backlight absorption and reduced phosphor efficiency with temperature can be addressed by using remote phosphor technology to fabricate white LEDs. Instead of using indium tin oxide (ITO), the new two-dimensional nanomaterals－graphene films (transmittance ＞ 90%) will be introduced into thin-film RCLED array to act as the transparent conductive layer. This helps to achieve the uniformity of current distribution on each emitter/pixel of the LED matrices so that the presence of nonunifrom light emission from the top surface of the LEDs operated at high levels of current injection can be avoided. Taking optical transmittance and structural strength into account, the Au doping process is preferentially used to reduce the sheet resistance (＜ 50 Ω/􀂅) of the as-grown graphene films. In addition, we shall focus on the development of highly reliable and defect-free transfer process for CVD grown graphene. In addition to being used as white-light sources, another interesting application based upon thin-film InGaN RCLEDs is free-space optical communications. 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 improve the performance of visible light communication systems, an angle-diversity receiver consists of an optical lens and a PIN array will be realized to collect optical signals. In addition, the signal to noise ratio of the receiver can be further improved as a clock and data recovery (CDR) circuit was introduced. With the use of advanced modulation schemes (e.g., quadrature amplitude modulation), we anticipate that visible light communications can transmit at a data rate higher than 300 Mbit/s.

Project ID:PB10408-5731
External Project ID:MOST104-2221-E182-055