Research on High Power Vertical Structure Gallium Nitride Light-emitting Diode Technology

[Source: Gaogong LED's "LED Good Products" magazine April issue (P60) Text /褚宏深] Vertical structure GaN-based light-emitting diode (GaN-based fluorescent-injection LED), can effectively improve the overall luminous efficiency, and can work at high current This is a function that traditional gallium nitride LEDs cannot achieve.

A conventional gallium-nitrogen light-emitting diode is a substrate in which electrothermally-insulated sapphire is epitaxially grown by gallium nitride. At high currents, current is congested and heat dissipation is not easy, so that large-size gallium-nitrogen light-emitting diodes for high-power operation cannot be fabricated. In this way, the scope of application of the component is limited.

Vertical structure gallium nitride LEDs have different images. The vertical current path avoids the thermal effects caused by current crowding and the photonic-radiativ erecombination of electrons and holes; in addition, the thermoelectric conduction substrate used in the vertical structure gallium-nitrogen light-emitting diode The high heat generated by the high-power operation of the module can obtain good heat dissipation treatment. The damage to the thermal effect component characteristics that is avoided by high-quality optoelectronic components does not occur here.

Therefore, to obtain a high-performance large-size solid-state light-emitting component, a vertical structure gallium-nitrogen light-emitting diode is a necessary choice. (See Figure 1.) A vertical structure high-power gallium-nitrogen light-emitting diode originally made of a sapphire substrate must be removed from the original sapphire substrate and a good thermoelectric conductive material as a new substrate material. In order to provide a large number of charge carrier light radiation composite uniform and convenient path and a good heat transfer medium under high current, as an effective heat dissipation path, thereby generating high optical power radiation.

(Figure 1) Traditional Gallium Nitrogen Light Emitting Diodes and Vertical Structure High Power Gallium Nitrogen Light Emitting Diodes

　　 The sapphire substrate stripping technology is the core technology of high-power gallium-nitrogen light-emitting diodes. At present, the technology of removing sapphire substrates by laser-lift off has been carried out for many years. Due to the high-energy laser induced on-chip defects and the destruction of the intrinsic characteristics of the chip material, such as the generation of leakage current, the reliability of the device is not good. Therefore, in the context of such manufacturing techniques, the production of vertical structure high power gallium nitride light emitting diodes is not widespread.

Sapphire is essentially an electrical insulator in electrical properties and does not have the good thermal conductivity necessary for the illuminating component. The characteristic defects of such an important substrate material essentially limit the development of high-power gallium-nitrogen light-emitting diodes.

This technical bottleneck can be solved by the sapphire stripping and new substrate material replacement technology that ASTRI has proposed. The main technical contents include: the non-laser sapphire stripping technology based on the complete chemical mechanical polishing (CMP) and component structure design developed by ASTRI, combined with innovative epitaxial structure design and undoped gallium. Undoped-GaN layer stripping technology.

In addition, this innovative sapphire stripping and substrate material replacement technology will be further integrated in technology by integrating the chip epitaxial structure design. (See Figure 2)

(Figure 2) Hong Kong ASTRI Vertical Structure High Power Gallium Nitrogen Light Emitting Diode: 2mm x 2mm

A large number of leakage current components cause low yield. It is the production bottleneck faced by high-energy laser stripping and sapphire substrate technology to produce vertical structure high-power gallium-nitrogen light-emitting diodes. The reason is that the high-energy laser induces damage to the intrinsic characteristics of the chip material caused by defects in the chip, and causes bad component conditions such as large leakage current and rapid light failure.

Unfinished: For more information, please refer to the April issue of Gaogong LED's "LED Good Products" magazine.