Researchers from the Low Energy Electronic Systems (LEES) Inter­disciplinary Research Group (IRG) at Singapore-MIT Alliance for Research and Technology (SMART), MIT's research enterprise in Singapore, together with Massa­chusetts Institute of Technology (MIT) and National University of Singapore (NUS) have found a method to quantify the distri­bution of compositional fluctuations in the indium gallium nitride (InGaN) quantum wells (QWs) at different indium concen­trations.

InGaN light emitting diodes have revolutionised the field of solid-state lighting due to their high effi­ciencies and durability, and low costs. The colour of the LED emission can be changed by varying the indium concen­tration in the InGaN compound, giving InGaN LEDs the potential to cover the entire visible spectrum. InGaN LEDs with relatively low indium amounts compared to gallium, such as the blue, green, and cyan LEDs, have enjoyed significant commercial success for communi­cation, industry and auto­motive appli­cations. However, LEDs with higher indium concen­trations, such as the red and amber LEDs, suffer from a drop in efficiency with the increasing amount of indium.

Currently, red and amber LEDs are made using the aluminium indium gallium phosphide (AlInGaP) material instead of InGaN due to InGaN's poor performance in the red and amber spectrum caused by the effi­ciency drop. Understanding and overcoming the effi­ciency drop is the first step towards developing InGaN LEDs covering the whole visible spectrum that would significantly reduce production costs. Now, the team employed a multi­faceted method to understand the origin of compo­sitional fluc­tuations and their potential effect on the effi­ciency of InGaN LEDs. The accurate deter­mination of compo­sitional fluc­tuations is critical to under­standing their role in reducing efficiency in InGaN LEDs with higher indium compo­sitions.

“The [origin of the] effi­ciency drop experienced in higher indium concen­tration InGaN LEDs is still unknown to this date,” says Silvija Gradecak from the Department of Materials Science and Engineering at NUS. “It is important to understand this effi­ciency drop to create solutions that will be able to overcome it. In order to do so, we have designed a method that is able to detect and study the compo­sitional fluctuations in the InGaN QWs to determine its role in the efficiency drop.” The researchers developed a multifaceted method to detect indium composi­tional fluctuations in the InGaN QWs using synergistic inves­tigation that combines complementary computational methods, advanced atomic-scale charac­terization and autonomous algorithms for image processing. Tara Mishra, SMART PhD Fellow, said, “This method developed and used in our research is of general applicability and can be adapted to other materials science inves­tigations where composi­tional fluc­tuations need to be inves­tigated.”

“The method that we developed can be widely applied and provide signi­ficant value and impact on other materials science studies, where atomistic composi­tional fluc­tuations play an important role in material performance,” said Piere­manuele Canepa, principal inves­tigator at SMART LEES. “The under­standing of the atomic distri­bution of InGaN at varying indium concen­trations is key to developing next-generation full-colour displays using the InGaN LED platform.” The research found that the indium atoms are randomly distributed in a relatively low indium content InGaN. On the other hand, partial phase separation is observed in higher indium content InGaN, where random composi­tional fluc­tuations are concurrent with pockets of indium-rich regions.

The findings advanced the understanding of the atomic microstructure of the InGaN and its potential effect on the performance of LEDs, paving the way for future research to determine the role of compositional fluctuations in the new generation of InGaN LEDs and design strategies to prevent the degradation of these devices. (Source: SMART)

Reference: T. P. Mishra et al.: Unlocking the origin of compositional fluctuations in InGaN light emitting diodes, Phys. Rev. Mat. 5, 024605 (2021); DOI: 10.1103/PhysRevMaterials.5.024605

Link: Singapore – MIT Alliance for Research and Technology, Singapore, Singapore