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

Abstract

In this paper, we report the successful demonstration of bright InGaN-based microLED devices emitting in the red spectral regime grown by metal organic chemical vapor deposition (MOCVD) on c-plane semi-relaxed InGaN substrates on sapphire. Through application of an InGaN/GaN base layer scheme to ameliorate high defect density and maintain appropriate lattice constant throughout the growth, high-In quantum wells (QWs) can be grown with improved crystal quality. Improvement to the design of the growth scheme also yields higher power output resulting in an increase to the external quantum efficiency (EQE). Combined, these two improvements allow for an 80 × 80 μm2 microLED device emitting at 609 nm to achieve 0.83% EQE. Furthermore, the true In content of the QW is measured using atomic probe tomography (APT) to confirm the improved In incorporation during high temperature active region growth. These developments represent advancement toward the realization of bright, highly efficient red III-nitride LEDs to be used in RGB applications under one material system.

Progress of InGaN-Based Red Micro-Light Emitting Diodes

“…GaN TJ offers a better current spreading and less optical loss, which can improve efficiency. These EQE values are one order higher than the previous reports about InGaN red µLEDs and represent the start-of-the-are results for InGaN red µLEDs [17,[19][20][21][22].…”

“…The 10 µm diameter circular 625 nm InGaN red µLEDs show an EQE of 0.14% at 8 A/cm 2 , despite the LEE estimated below 4%. Moreover, White et al from UCSB and Soitec have greatly improved the EQE of 80 × 80 µm 2 609 nm InGaN µLEDs on InGaNOS to 0.83% by reducing the defect density in the InGaN/GaN buffer layer and optimizing the p-type structure [18,19]. Noted that the growth temperature for red QWs on InGaNOS is much higher than the typical red QWs grown on GaN template (close to green InGaN QWs growth temperature).…”

“…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.…”

Demonstration of 621-nm-wavelength InGaN-based single-quantum-well LEDs with an external quantum efficiency of 4.3% at 10.1 A/cm2

“…4(b). 16,18,20,21,23,26,33,[37][38][39][40][41] We also calculated the EQEs and WPEs of the LEDs at various injection currents, as shown in Fig. 5.…”

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

“…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.…”