Recent Progress in Long‐Wavelength InGaN Light‐Emitting Diodes from the Perspective of Epitaxial Structure

Abstract

Over the last decades, continuous technological advancements have been made in III‐nitride light‐emitting diodes (LEDs), so that they are considered as a promising replacement of traditional light sources. With the emission wavelength covering the entire visible spectrum, InGaN LEDs find various applications such as solid‐state lightings, full‐color displays, and visible light communication. However, the quantum efficiency of InGaN LEDs suffers from a dramatic decline as the emission wavelength extends from blue to green–red region. This issue restrains the lighting and display applications based on the color‐mixing monolithic lighting source system. In this review, the recent breakthroughs in long‐wavelength InGaN LEDs, together with the challenges and approaches to realize high‐indium‐composition InGaN epilayers, are introduced. These cover the different epitaxial substrates, nucleation layers, and epitaxial structures, especially multiple quantum wells active region. The related studies are also discussed to improve the long‐wavelength LEDs performance from the aspect of crystal quality, growth orientation, carrier‐injection, and 3D nanostructures. Finally, current status and perspectives for future long‐wavelength LEDs development are proposed briefly.

Cathodoluminescence studies of the optical properties of a zincblende InGaN/GaN single quantum well

“…Furthermore, we note that these pale stripes tend to locally lie mostly along the same orientation (similar to arrow-3 in figure 1(a)) along [110]. Additionally, we also observe a lower density of pale stripes along [1][2][3][4][5][6][7][8][9][10] direction. This is consistent with previous study which shows an anisotropy of SF orientation in similar samples [16].…”

“…The elongated features are observed to be aligned both perpendicular and parallel to the miscut direction, i.e. in both the [1][2][3][4][5][6][7][8][9][10] direction and the [110] direction, marked by arrow-1 and arrow-2 in figure 1(a), respectively. Furthermore, pale stripes are observed on the surface, parallel to the [110] miscut direction, marked by arrow 3 in figure 1(a).…”

“…Additionally, to reach green emission, either more indium needs to be incorporated into the InGaN/GaN QWs or the QW thickness needs to be increased, in comparison to blue light emitting QWs. This increase in the InN content in the QWs is typically achieved by growing the heterostructure at a lower temperature, which has been suggested to lead to incorporation of a higher density of point defects and can possibly increase the inhomogeneity of the InN composition in the QWs [9][10][11]. Such point defects may act as non-radiative recombination centres, while any inhomogeneity of the InGaN QWs can lead to poor spectral purity of wz-based InGaN/GaN QWs [12][13][14].…”

Recent advances in micro-pixel light emitting diode technology

“…In particular, the growth of an InGaN QW layer with a high indium content requires lower temperatures, which leads to poor crystal quality. 16,17,158,159 Furthermore, this InGaN layer increases the strain due to lattice mismatch, resulting in defects such as threading dislocations and trench defects.…”

Droop and light extraction of InGaN-based red micro-light-emitting diodes

“…This consequently leads to the problem of how to realize a high light output at longer wavelengths. Indeed, InGaN-based red µLEDs with a longer emission wavelength encounter a low EQE due to structural defects such as dislocations, stacking faults and trench defects [14]. To overcome this, a method for improving the light extraction efficiency (η e ) of µLEDs is attracting attention as a strategy for dealing with degradation of the EQE of µLEDs [15][16][17][18][19].…”