True-Red InGaN Light-Emitting Diodes for Display Applications

Red InGaN has attracted much attention recently for micro-light-emitting diode (microLED) display applications. However, the consequences of spectral broadening are often overlooked and many of the published spectra do not meet display gamut requirements. Herein, maximizing the red InGaN radiance with a spectrum capable of meeting the digital cinema initiatives-protocol 3 standard (dominant wavelength of approximate to 615 nm) is focused on. The maximum radiance for LEDs meeting said requirement is obtained at 20 A cm-2 and corresponds to 4% wall-plug efficiency (WPE) in large-area encapsulated devices. The WPE can be increased to 12.5% using epitaxy of lower In concentration driven at 2 A cm-2. Also, data for microLEDs fabricated from similar red InGaN epitaxy are reported. No size dependence of the internal quantum efficiency or spectra is observed down to the smallest sizes studied (approximate to 2 mu m). Herein, expertise with red InGaN and nitride tunnel junctions is further leveraged to demonstrate polychromatic microLEDs with independent control of red, green, and blue emission within single pixels of 9 x 12 mu m dimensions. These devices are grown in a single growth run on the same sapphire substrate wafer using methods proven in high-volume epitaxy manufacturing. Red InGaN technology can potentially realize microdisplays fabricated by monolithic integration instead of mass die transfer. Herein, the display gamut requirements and physical properties of InGaN that make it challenging to meet them are discussed. The state-of-the-art performance for standalone red InGaN light-emitting diodes (LEDs) and a demonstration of color-tunable microLED pixels fabricated from a single epitaxial wafer are presented.image (c) 2024 WILEY-VCH GmbH