True‐Red InGaN Light‐Emitting Diodes for Display Applications

Abstract

Red InGaN has attracted much attention recently for microLED display applications. However, the consequences of spectral broadening are often overlooked and many of the published spectra do not meet display gamut requirements. We focus on maximizing the red InGaN radiance with a spectrum capable of meeting the DCI‐P3 standard (dominant wavelength of ∽615 nm). The maximum radiance for LEDs meeting said requirement is obtained at 20 A/cm2 and corresponds to 4% WPE in large‐area encapsulated devices. The WPE can be increased to 12.5% using epitaxy of lower In concentration driven at 2 A/cm2. We also report data for microLEDs fabricated from similar red InGaN epitaxy. No size dependence of the IQE or spectra are observed down to the smallest sizes studied (∽2 microns). We have further leveraged our expertise with red InGaN and nitride tunnel junctions to demonstrate polychromatic microLEDs with independent control of red, green, and blue emission within single pixels of 9x12 micron dimensions. These devices are grown in a single growth run on the same sapphire substrate wafer using methods proven in high‐volume epitaxy manufacturing.This article is protected by copyright. All rights reserved.

Recent advances in micro-pixel light emitting diode technology

“…The EQE is divided into three groups: AlGaInP LEDs (sky blue symbol), 68,80,86,151,153,180 InGaN LEDs emitting wavelengths over 625 nm (red symbol), 51,67,77,160,161,165,166,171,[181][182][183][184][185][186][187][188][189] and InGaN LEDs emitting wavelengths less 625 nm (green symbol). 66,163,168,169,188,[190][191][192][193][194][195][196][197][198][199] The EQE of the AlGaInP LEDs tends to decrease with a smaller size. This is typically attributed to the significant carrier loss at the sidewall due to a relatively long diffusion length.…”

“…Nonetheless, the low EQE of InGaN red LEDs can be overcome through optimized growth conditions and device processing, including sidewall passivation and reflectors to improve light extraction efficiency. 171,185,199 However, in terms of efficiency, it remains an open question as to whether AlGaInP-or InGaNbased red lLEDs are suitable for the typical resolution regime for lLED displays (e.g., 1000-10 000 PPI).…”