Realization of III-Nitride c-Plane microLEDs Emitting from 470 to 645 nm on Semi-Relaxed Substrates Enabled by V-Defect-Free Base Layers

Abstract

We examine full InGaN-based microLEDs on c-plane semi-relaxed InGaN substrates grown by metal organic chemical vapor deposition (MOCVD) that operate across a wide range of emission wavelengths covering nearly the entire visible spectrum. By employing a periodic InGaN base layer structure with high temperature (HT) GaN interlayers on these semi-relaxed substrates, we demonstrate robust μLED devices. A broad range of emission wavelengths ranging from cyan to deep red are realized, leveraging the indium incorporation benefit of the relaxed InGaN substrate with an enlarged lattice parameter. Since a broad range of emission wavelengths can be realized, this base layer scheme allows the tailoring of the emission wavelength to a particular application, including the possibility for nitride LEDs to emit over the entire visible light spectrum. The range of emission possibilities from blue to red makes the relaxed substrate and periodic base layer scheme an attractive platform to unify the visible emission spectra under one singular material system using III-Nitride MOCVD.

InGaN-Based microLED Devices Approaching 1% EQE with Red 609 nm Electroluminescence on Semi-Relaxed Substrates

“…This base layer was also designed to match the lattice constant of the substrate, maintaining the relaxed strain state present initially. With a base layer free from V-defects and with good morphology, the advantages of the relaxed InGaN substrate and increased lattice constant can be used in the realization of µLED devices [18]. Importantly, the reduction of the compositional pulling effect resulting from the reduction in strain during growth can then be applied to QW growth, allowing for higher temperatures to be used while still achieving high In content in a red-emitting device.…”

Low Forward Voltage III-Nitride Red Micro-Light-Emitting Diodes on a Strain Relaxed Template with an InGaN Decomposition Layer

“…Figure 3a shows the current density-voltage characteristics of the µLEDs. All the devices yielded a low forward voltage, showing voltage values between 2.00 V and 2.05 V at 20 A/cm 2 , which is the lowest voltage characteristic compared to other InGaN red emitters in the literature [9,15,19,[28][29][30]. The low voltage could be attributed to the better hole The InGaN red devices yielded exceptional electrical and optical performances, including low forward voltage and relatively high light output power (LOP) characteristics.…”

“…Nevertheless, the FWHM was very broad for display applications, and decreased from 90 nm at 5 A/cm 2 to 66 nm at 35 A/cm 2 and increased gradually to 70 nm at 100 A/cm 2 . For InGaN-based LEDs, the FWHM generally increased with wavelength emission due to indium fluctuation in the active region [9]. The reduction in electroluminescent FWHM from 5 to 35 A/cm 2 could be due to emission from delocalized band states, while the increase in FWHM at higher current densities could be attributed to bandgap normalization due to an increase in junction temperature or excited states [24,25].…”

“…Among the three required colors, III-nitride red µLEDs remain a critical challenge due to the increased strain in the active region attributed to the 10% lattice mismatch between InN and GaN [7]. Therefore, several novel methods have been demonstrated to reveal the possibility of III-nitride red LEDs by employing strain engineering in the active region, such as semi-relaxed InGaN substrates and porous GaN pseudo-substrates [8][9][10][11][12][13]. However, most of the proposed techniques require patterning and regrowth, which can be problematic for scalability and manufacturing perspectives.…”

Progress of InGaN-Based Red Micro-Light Emitting Diodes

“…More recently, we reported InGaN red µLEDs with an EQE over 3% using similar active region design [5][6][7]. Other novel growth strategies have been proposed to achieve InGaN red µLEDs, such as InGaNOS pseudo-substrate [16][17][18][19], nano-porous GaN [20], strain relaxed InGaN buffer layer using in-situ InGaN decomposition layer [21,22]. These technologies aim to relax the strain of InGaN buffer layer and increase the indium intake efficiency in the red InGaN QWs.…”