Efficient InGaN‐Based Red Light‐Emitting Diodes by Modulating Trench Defects

Abstract

Trench defects in multi‐quantum wells (MQWs) have been considered as flawed structures that severely degraded the internal quantum efficiency (IQE) of light‐emitting diodes (LEDs) in the past. In this research, trench defects are innovatively utilized to enhance the efficiency of red InGaN LEDs. Specifically, dual‐color MQWs structures are applied to modulate trench defects. The upper red MQWs, grown on top of green MQWs with a high density of trench defects, exhibit a significant wavelength redshift of 68 nm and ≈ 6‐fold luminescence enhancement compared to those without intentionally introduced trench defects. Red InGaN LEDs with an IQE of 16.4% are achieved with this epitaxy growth strategy. Such wavelength redshift is attributed to the more indium incorporation due to the strain relaxation effect of trench defects. Moreover, the luminescence enhancement originates from the strong emission of the red MQWs inside trench defects, mainly attributed to strain relaxation and defect shielding by the wide and deep trenches. Achieving red emission by modulating trench defects is simple and reproducible without requiring additional substrate designs, which provides a novel way toward high‐efficiency red InGaN LEDs.

Thermally stable radiative recombination centers within trench structures of red multi-quantum wells

“…In figure 1(c), dot-like luminescence inside the trench structures can be observed, with an average integral intensity about 3.2 times higher than that of the surrounding regions. The detailed analysis of trench morphologies by AFM and CL comparison reveals that luminescence enhancement occurs only in red QWs inside deep trenches [26]. The BSFs of these deep trench structures originate from the underlying green MQWs, which are introduced intentionally by low-temperature growth.…”

“…As shown in figure 1(a), the BSFs and SMBs of these trench defects are embedded in the green MQWs without affecting the luminescence of the upper red MQWs. These intentionally introduced deep trench structures can facilitate stress relaxation in red MQWs, thereby enhancing the In incorporation [26]. Moreover, these deep trenches can lead to carrier localization, weakened polarization effect, and lower defect density of the red MQWs inside trenches.…”

“…Moreover, these deep trenches can lead to carrier localization, weakened polarization effect, and lower defect density of the red MQWs inside trenches. These factors combined contribute to a higher radiative recombination efficiency of red MQWs inside trenches [26].…”

“…In contrast, the emission from the green MQWs nearly disappears. In [26], the p-GaN layers were grown on the similar dual-colour MQW sample at about 935 • C for 1200 s. The red QWs inside trenches can still emit light efficiently after the p-GaN growth. As a reference, green MQWs with high QW/barrier temperatures of 700 • C/820 • C showed a 72% decay in PL intensity after the same annealing process (not shown here).…”

“…Luminescence enhancement and wavelength redshift of QWs can be observed within these trench structures [23][24][25]. In this study, red emission was achieved by modulating trench structures in dual-colour MQW structures (details in [26]). Remarkably, the red MQWs inside deep trenches exhibited superior thermal stability despite being grown at low temperatures.…”