Design and Fabrication of Near-Ultraviolet Micro-Cavity Light-Emitting Diode Array for Solid-State Lighting

The luminous efficiency of a new light-emitting diode (LED) luminaire has reached commercial levels, but further increases in emission efficiency and light intensity is still needed to maximize energy savings and to reduce manufacturing costs, thus accelerating the adoption of efficient solid-state lighting based on white light LEDs. To fulfill the requirements of next-generation energy-saving luminaire, we seek to design and fabricate a near-UV micro-cavity light emitting diode array (Near-UV MCLED array) for directional task illumination. Experimentally, an asymmetric multiple-quantum-well (MQW) is introduced along with a strain-compensated superlattice barrier (SC-SLB) to alleviate the phenomenon of efficiency droop, thus further improving the fabricated MCLED array’s light output power at high injection current levels. On the other hand, the use of flip-chip packaging not only increases the amount of light emitted from the LEDs but also helps to improve thermal dissipation during LED operation. For general white light LED packages, the LED chips were first mounted in the reflective cup and the phosphor silicone was then freely dispersed on top. While this approach increases the ease of manufacturing, the inherent lack of precise control of the thickness and shape of the phosphor layer results in inconsistent colors along the emission directions. In addition to the reducing phosphor efficiency with temperature, LED chips have more opportunities to absorb backscattered lights, thus significantly degrading the emission properties of white light LEDs. In contrast, removing the phosphor layer from the chip through a remote phosphor technique can increase the light intensity of white light LEDs while stabilizing the emission color. The program schedule is organized as: 1. In the first year: we will take work to accurately control the thickness, doping concentration, and composition of each epitaxial layer during MOCVD growth of Near-UV LEDs. Further reducing material defects by modifying the GaN template layers helps increase the internal quantum efficiency of the LEDs. An asymmetric MQW, in combination with a SC-SLB, can be used to increase hole distribution uniform among the wells and to alleviate the polarization effects within the MQW region. 2. In the second year: we shall focus on the realization of Near-UV MCLEDs with an AlGaN/GaN distributed Bragg reflector (DBR). Although the increase in the reflectivity of the upper mirror can improve the spectral purity and directionality of the MCLEDs, the amount of light bouncing back and forth in the resonant cavity is increased, thus significantly deteriorating the radiative efficiency of the MCLEDs. Therefore, flip-chip packaged MCLED array will be experimentally fabricated to enhance the light output power. Finally, we anticipate that white light LEDs fabricated by remote phosphor technology could have a light intensity and color rendering index respectively greater than 400 lumens (luminous efficiency ＞ 90 lm/W) and 80. Besides, the beam emission angle can be further reduced below 50o as compared to that of their counterparts.

Project ID:PB10108-2800
External Project ID:NSC101-2221-E182-036