Will nanowire LEDs be the ultimate light engine for AR and VR displays? - Tech Xplore

High solution density, wide tract of presumption (FoV), lightweight and compact formfactor, and debased powerfulness depletion are demanding requirements for augmented world (AR) and virtual world (VR) displays. Compared to liquid crystal displays (LCDs) and integrated light-emitting diode (OLED) displays, microLED is attracting much attraction owed to its precocious highest brightness, fantabulous acheronian state, precocious solution density, tiny formfactor, and agelong lifetime.

On the different hand, arsenic the spot size decreases, the microLED ratio decreases owed to sidewall defects. Therefore, the tradeoff of high-resolution density and outer quantum ratio (EQE) is simply a large situation to applying microLED arsenic an AR/VR airy engine, successful summation to precocious fabrication cost.

Nanowire LEDs amusement large imaginable for achieving high-resolution density and precocious EQE astatine the aforesaid time. Since each pixel is formed by submicron nanowire array, the ratio of the nanowire LED is autarkic of pixel size. In 2018, Aledia reported a nanowire LED whose EQE is autarkic of transportation size erstwhile the transportation size is reduced from 1000 μm to 5 μm.

Among antithetic nanowire structures, InGaN/GaN dot-in-wire hexagonal LED is charismatic due to the fact that its emanation wavelength tin beryllium controlled by the ligament diameter and its electrical show is excellent. The erstwhile diagnostic importantly reduces the fabrication difficulties. However, these nanowires grounds antithetic angular radiation patterns for the red, greenish and bluish colors successful the far-field, starring to a noticeable angular colour shift.

Additionally, directional airy motor is preferred since the accepting cone successful AR/VR imaging strategy is typically wrong ±20°. Therefore, the geometry of the nanowire should beryllium optimized to execute matched radiation patterns for the 3 superior colors, precocious airy extraction ratio (LEE), and constrictive angular luminance organisation simultaneously.

The authors of an nonfiction precocious published successful Opto-Electronic Science optimized the InGaN/GaN nanowire LED geometry by 3D dipole unreality done a commercialized question optics simulation bundle Finite-Difference Time-Domain (FDTD, Ansys inc.). They suggest a multicolor hexagonal azygous InGaN/GaN dot-in-nanowire LED exemplary based connected Ra's experimental results.

They acceptable a 3D ample container show and tiny container show to cipher the emanation powerfulness and dipole power, respectively, which defines the airy extraction ratio (LEE) by their ratio. Additionally, the far-field organisation representation is captured by a 2D powerfulness show placed supra the structure.

As indicated successful Fig. 1(b), owed to the hexagonal symmetry, they simulate 2 groups of dipoles which are defined by an inscribed ellipse and circumscribed circle, respectively. The emanation wavelength of the dipole sources follows the unfiltered measured emanation spectra (solid lines successful Fig. 1(c)). All 3 nanowires without colour filters person broadside lobe emanation since the Indium adatom diffusion is hard to beryllium perfectly controlled. As indicated successful the dashed lines successful Fig. 1(c), this broadside lobe emanation is suppressed dramatically aft applying colour filters.

Figure 2(a–c) depicts the calculated normalized 2D angular organisation for blue, green, and reddish nanowire LEDs, respectively. By sweeping the p-GaN capping tallness and vertical presumption of progressive layers, the authors find the optimal conditions for blue, green, and reddish nanowire LEDs.

By considering the AR imaging strategy accepting cone, the authors specify the effectual LEE to beryllium the LEE wrong ±20°. After optimization, the effectual LEE of blue, green, and reddish nanowire LEDs increases from [9.3%, 18.8%, 30.6%] to [10.0%, 25.6%, 33.0%], respectively. In examination with the size-dependent bluish and greenish InGaN µLED and assuming 100% of the produced airy tin beryllium coupled into the imaging system, their bluish nanowire LED shows a amended show than µLED whose mesa size is smaller than 10 µm arsenic shown successful Fig. 3(a).

In addition, Fig. 3(b) indicates that the effectual LEE of greenish nanowire LEDs is adjacent higher than that of the 80-µm µLED. Compared to AlGaInP reddish µLEDs, their reddish nanowire LED is much businesslike than that with 20-µm spot size (Fig. 3(c)). Remarkably, successful examination with the 10-µm mesa size, the bluish nanowire LED provides a akin brightness, portion greenish and reddish nanowire LEDs tin connection 1.6x and 1.4x higher efficiency, respectively. Therefore, nanowire LEDs amusement a pronounced higher ratio than µLED nether tiny pixel size and high-resolution density.

More information: Yizhou Qian et al, Directional high-efficiency nanowire LEDs with reduced angular colour displacement for AR and VR displays, Opto-Electronic Science (2022). DOI: 10.29026/oes.2022.220021

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