According to foreign media reports, the University of California, Santa Barbara (UCSB) announced that it has demonstrated for the first time InGaN-based red micro LED chips with a size of less than 10 microns, and measured on wafers. The outbound quantum efficiency (EQE) is 0.2%.
Improving external quantum efficiency still has a long way to go
Previously, French semiconductor materials company Soitec, which has the ability to mass-produce InGaN-based red Micro LED chips, released 50-micron InGaN-based red Micro LED devices in 2020. However, Shubhra Pasayat, a spokesperson for the UCSB team, pointed out that Soitec No data on external quantum efficiency has been released.
Pasayat said that Micro LEDs smaller than 10 microns are critical to the viable commercialization of the Micro LED industry. At the same time, in addition to the small size, the external quantum efficiency of the Micro LED chip must be at least 2-5% to meet the requirements of the Micro LED display.
However, the external quantum efficiency of the InGaN-based red Micro LED chip displayed by UCSB this time is only 0.2%. In this regard, Pasayat said frankly that although the current research results of the team are far from reaching the goal, the relevant research work has entered the preliminary stage and substantive progress can be expected in the future.
The next goal of the UCSB team is to improve the external quantum efficiency of the red light Micro LED chip. It is currently planning to improve the quality of the materials and improve the production steps.
InGaN material application prospects can be expected
It is also worth noting that the UCSB team is studying InGaN-based red Micro LEDs instead of AlGaInP-based red Micro LEDs, mainly because the efficiency of the latter usually decreases as the size decreases. Pasayat revealed that, so far, the minimum size of AlGaInP-based red Micro LED chips is 20 microns, and the external quantum efficiency is unknown.
It is understood that the current red LEDs are mostly made of AlGaInP materials, and their efficiency is as high as 60% or more under the normal chip size. However, when the chip size is reduced to the order of micrometers, the efficiency will drastically drop below 1%.
In addition, in the mass transfer process, the disadvantages of AlGaInP materials are also obvious.
Mass transfer requires the material to have good mechanical strength to avoid cracking during chip picking and placement, while the poor mechanical properties of AlGaInP material will add new problems to mass transfer.
In contrast, InGaN films have advantages such as adjustable wide band gaps, and have broad application prospects in the visible light field, and Micro LED full-color display is one of the most potential applications.
It is reported that InGaN material has better mechanical stability and shorter hole diffusion length, and is compatible with InGaN-based green and blue Micro LEDs, so it is a better choice for red Micro LEDs.
It is worth noting that the team of Academician Jiang Fengyi announced a research breakthrough in high-efficiency InGaN-based orange-red LEDs last year. The research results also proved that InGaN materials will have great potential in the production of red-light pixel chips for display applications.
In addition, UCSB and Seoul Viosys have conducted research on the trend of changes in the external quantum efficiency of Micro LEDs smaller than 5 microns in size. Based on the research results, they believe that InGaN-based red micro LEDs are expected to help manufacture smaller-sized full-color Micro LED displays.
At the same time, the two parties hope to promote the use of smaller InGaN-based Micro LEDs in high-end display fields such as smart phones, AR glasses and 4K TVs through factors such as improved brightness and reliability.