Beyond solid-state lighting: Miniaturization, hybrid integration, and applications of GaN nano- and micro-LEDs

Abstract

Gallium nitride (GaN) light-emitting-diode (LED) technology has been the revolution in modern lighting. In the last decade, a huge global market of efficient, long-lasting, and ubiquitous white light sources has developed around the inception of the Nobel-prize-winning blue GaN LEDs. Today, GaN optoelectronics is developing beyond solid-state lighting, leading to new and innovative devices, e.g., for microdisplays, being the core technology for future augmented reality and visualization, as well as point light sources for optical excitation in communications, imaging, and sensing. This explosion of applications is driven by two main directions: the ability to produce very small GaN LEDs (micro-LEDs and nano-LEDs) with high efficiency and across large areas, in combination with the possibility to merge optoelectronic-grade GaN micro-LEDs with silicon microelectronics in a hybrid approach. GaN LED technology is now even spreading into the realm of display technology, which has been occupied by organic LEDs and liquid crystal displays for decades. In this review, the technological transition toward GaN micro- and nanodevices beyond lighting is discussed including an up-to-date overview on the state of the art.

Nonmechanical parfocal and autofocus features based on wave propagation distribution in lensfree holographic microscopy

“…Instead of employing a laser as the light source, an LED was integrated into the lensfree microscope (Fig. 1a,b) mainly because of its partial coherence characteristic, stable intensity, and harmlessness to living samples or CMOS image sensors 28,58 . However, the spatial coherence of the LED-illumination has to be adjusted to reduce the geometric unsharpness.…”

“…In respect to the base material, gallium nitride (GaN)-based LED has been widely accepted and employed as a promising solid-state light source because of its high efficiency, robust structure, high brightness, fast modulation, and long lifetime. These are achieved not only for large-area high power LEDs used in solid state lighting, but also for LEDs with dimensions of below 10 µm (i.e., microLEDs) as structured micro-illumination sources [28][29][30][31][32] . To support the development of the compact microscope, micro-and nanoscale GaN-based LEDs can be fabricated using either bottom-up or top-down approach, as well as processed to be a highly integrated pinhole microLED array, which is beneficial for increasing spatial coherence and hence the imaging capability 22,[33][34][35][36] .…”

Recent Advances on Thermal Management of Flexible Inorganic Electronics

“…Microscale inorganic light-emitting diodes, as a typical inorganic electronic device, show excellent interactions with biological tissues as excitation sources. For example, µ-ILEDs can be an alternative excitation source to an optoelectronic tweezer via noncontact manipulation methods to investigate behaviors of various biological samples such as cells [26][27][28][29][30][31][32], proteins [33], DNA molecules [34,35] and particles [36,37]. In addition to the above applications, µ-ILEDs can also be adopted in optogenetics to control, affect and readout the neural activities of biological creatures, especially for stimulation in brain [38][39][40][41], retina [42][43][44], and audition [45][46][47][48][49].…”

Directly addressable GaN-based nano-LED arrays: fabrication and electro-optical characterization

“…However, both methods are not suitable for an arrangement of structures in dense arrays, which would result in very complex addressing schemes. On the other hand, reported LED sizes in individually controllable arrays that are targeted for microdisplay technologies, start from 5 μm, as a greater size reduction would not be suitable for integration with ASICs, which are used for active LED driving 8,9 . Here, we report on a strategy to go beyond existing approaches by developing even smaller LEDs with dimensions comparable or smaller than the wavelength of visible light, targeting dimensions of 500 nm and below.…”