Light-Emitting Diodes

Micro/nano LED


Because of the paradigm shift of future industries, represented by big data and artificial intelligence, GaN-based LEDs used for low-power/high-output illumination light sources are gradually ultraminiaturized and highly integrated by the technological advances of micro-/nano-LEDs and pixel-wafer level chip-scale package.


InGaN-AlGaN-GaN semiconductors are the best candidates for the fabrication of micro-LED. Theoretically, the nitride semiconductors could make it possible to realize light-emitting devices of visible regions, including infrared and ultraviolet spectra. In particular, GaN covers band-gaps ranging from 0.7 to 6.2 eV, depending on the In or Al contents, and hence is very suitable for the fabrication of visible light-emitting devices.



Trend



According to the trend of future technological advances, the development of IoT, wireless communication, and flexible display areas needs technologies such as ultraminiaturization, high-density integration, and use of flexible substrates. These require the realization of micro-/nano-LED and pixel-wafer level chip-scale package that are of a high level of technological difficulty.


Application



Realization of ultraminiaturized self-emitting light sources requires a functional need. Conventional GaN-LED chips cannot overcome the bending characteristics of inflexible inorganic materials unless their sizes are reduced down to a micron-size level. These have a wide variety of applications in the areas of large-scale flexible display, smart fibers (fibers-combined with LEDs), medical appliances that can be attached to or implanted into body, bio-contact-lens, head-mounted display (HMD), and wireless communication.


High wall plug efficiency



Fabrication of high-efficiency visible LEDs requires the development of core technologies, namely, enhancement of internal quantum efficiency (IQE), current injection efficiency (CIE), and light extraction efficiency (LEE).


IQE is directly related to the quality of GaN epitaxial layers, multi-quantum wells (MQWs), and hetero-junction quantum structures. CIE depends on the design of MQB (multi-quantum barrier), cascade quantum barrier, and the design of injection electrodes. LEE is also critically affected by technologies such as chip platform, transparent conductive electrode materials, distributed Bragg reflector (DBR) and omnidirectional reflector (ODR), and photonic structures.