Characteristics of Stacked GaInN-Based Red, Green, and Blue Full-Color Monolithic μLED Arrays Connected via Tunnel Junctions

The use of μLEDs in self-luminous displays is crucial for the development of high-efficiency displays for virtual space services. For this purpose, a stacked monolithic GaInN-based micro light-eimtting diodes (μLED) device that emits red, green, and blue (RGB) light is obtained. The RGB layers are connected via tunnel junction (TJ) layers. The pixel density is 330 ppi (35 × 15 μm² of μLED mesa area corresponding to the emission). The cross-sectional transmission electron microscopy analysis indicates that there is not a significant increase in threading dislocations even after stacking the three RGB active layers and two TJ layers. In addition, the X-ray diffraction reciprocal lattice space mapping shows that all the layers grow almost coherently with respect to the GaN substrate. A detailed evaluation of the resulting device shows that the BT.2020 color gamut coverage reaches a maximum of 71%, and the luminance is sufficiently high for head-mounted display applications. Redshifting of the emission wavelength of the red μLEDs by increasing the InN mole fraction in the GaInN active layer would likely lead to improvement of the color gamut coverage in future studies.