Unexpectedly Simultaneous Increase in Wavelength and Output Power of Yellow LEDs Based on Staggered Quantum Wells by TMIn Flux Modulation

Abstract

Pursuing efficient long-wavelength InGaN LED has been a troublesome issue to be solved, which forms interesting subjects for fundamental research, but finds also motivation in extensive applications. Here, we investigate the effect of TMIn (trimethylindium) flux variation for growing bandgap-engineered staggered quantum wells (QWs) on corresponding LED properties and demonstrate the unexpectedly simultaneous increase in light output power (LOP) and emission wavelength. At 20 mA, LEDs based on staggered QWs grown under low flux show an increase of 28% in LOP and longer wavelength compared to that under high flux. The experimental results reveal that TMIn flux affects crystalline quality and indium composition of epilayers. Under high TMIn flux, high in-plane strain exists between adjacent layers, accompanied by the composition pulling effect, which reduces indium incorporation for the following staggered QW growth and hinders realization of yellow light emission. According to simulation results, low-flux-grown staggered QWs contribute to increased carrier wavefunction overlap as well as enhanced electric field. Notably, the former enables high LOP, while the latter results in emissions towards long wavelength, promising to solve an ever-present concern that LED performance deteriorates with increasing emission wavelength. Therefore, this work shows great significance in thoroughly understanding growth conditions for bandgap-engineered staggered QW structures, which offers a facile solution to achieve efficient long-wavelength optoelectronics devices.

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

“…Interestingly, the simultaneous increase in LOP and emission wavelength could be realized in LEDs based on staggered QWs. [ 73 ] By modulating the low‐indium‐composition layer of staggered QWs, carrier wavefunction, indium incorporation, and electric field in the following high‐indium‐composition layer can be simultaneously modulated. Less indium composition in low‐indium‐composition not only enhances the carrier wavefunction overlap, but also enhances the electric filed and alleviates composition‐pulling effect.…”

Performance Improvement of InGaN-Based Red Light-Emitting Diodes via Ultrathin InN Insertion Layer

“…Another difficult issue is that the IQE of LEDs drastically drops under a high injection current, which is caused by Auger recombination [14,15]. To alleviate the strong QCSE and efficiency droop, energy band engineering strategies are extensively proposed, including the quantum dots [16], the semior non-polar structures of InGaN [17][18][19], the graded electron block layer (EBL) [20,21], the staggered quantum wells (QWs) [22][23][24][25][26], the strain compensation layer on QW [27], and other QWs structures [28][29][30]. However, these strategies are rarely used in InGaN-based red LEDs and the corresponding mechanism needs to be further investigated.…”

A Simulation Study of Carrier Capture Ability of the Last InGaN Quantum Well with Different Indium Content for Yellow-Light-Emitting InGaN/GaN Multiple Quantum Wells

“…In fact, for yellow-light-emitting InGaN/GaN multiple quantum wells (MQWs), the depth of the quantum potential well of InGaN layers is relatively deeper due to the relatively higher In content in InGaN layers compared to the conventional blue InGaN QWs. Therefore, during the electroluminescence (EL) process, combined with the notable difference in mobility between electrons and holes, most electrically injected electrons and holes can be easily accumulated in the last InGaN quantum well (LIQW), which is the closest InGaN QW to the P-type region [ 16 ]. As a result, the luminescence emission is mainly contributed by the carrier radiative recombination in the LIQW.…”