1. Field of the Invention
The present invention generally relates to a light emitting diode (LED), and more particularly to a method of forming laterally distributed red, green and blue (RGB) LEDs on a chip.
2. Description of the Prior Art
Light emitting diodes (LEDs), particularly white LEDs, have been increasingly used as backlighting for liquid crystal displays (LCDs) of mobile phones and notebook computers. Moreover, red, green and blue (RGB) LEDs are usually color mixed to obtain better lighting characteristics.
However, the performance and illuminance efficiency of mixing state-of-the-art RGB LEDs are low and the cost of packaging to combine RGB LEDs is high. For example, with respect to a conventional technique, discrete LED components are assembled on a package as shown in FIG. 1A. In an improved Chip-on-Board (COB) technique, as shown in FIG. 1B, the RGB LED chips are directly mounted on the package, rather than a more traditional assembling of the discrete LED components. Therefore, the height of the COB package (FIG. 1B) is smaller than the height of the discretely assembled package. Further, the minimum interval between adjacent LEDs using the COB technique may accordingly be decreased to reach about 2 mm, while the minimum interval between adjacent LEDs using discrete assembling techniques may be as large as 5 mm. Nevertheless, the 2 mm interval using the COB technique is still too large to arrive at high performance and illuminance efficiency without additionally, and thus costly, using a reflector and a light guide plate (LGP).
A conventional structure and method of fabricating vertically stacked LEDs on a chip is disclosed, for example, in “Multi-color Light Emitting Diode Using Polarization-induced tunnel Junctions,” Phys. Stat. Sol. (c) 4, No. 7, 2830-2833 (2007), by Michael J. Grundmann et al. In that publication, vertically stacked LEDs are provided with electroluminescence properties that often change disadvantageously with injection current.
Another prior art structure and method of fabricating laterally distributed LEDs on a chip is disclosed, for example, in “Phosphor-free White Light-emitting Diode with Laterally Distributed Multiple Quantum Wells,” Applied Physics Letters 92, 091110 (2008), by Il-Kyu Park et al. In the disclosed process, the etching of the multiple quantum wells will incur surface damage, which results in low illuminance efficiency.
For the reason that conventional LEDs could not be effectively combined to obtain better lighting characteristics, a need has arisen to propose a novel scheme for fabricating LEDs with stable output efficiency, simple packaging, high color mixing efficiency and reduced chip area.