From Large‐Size to Micro‐LEDs: Scaling Trends Revealed by Modeling

Abstract

General trends in scaling dimensions of a circular‐shaped flip‐chip light‐emitting diode (LED) are studied by coupled electrical‐thermal‐optical simulations. Advanced chip design is considered, providing high efficiency of light extraction through the top surface of the LED die. The simulation model accounts for such important effects, as current crowding near metallic electrodes, thermal and non‐thermal efficiency droop caused by Auger recombination, and surface recombination at the edges of the LED active region. Interplay and competition of the mechanisms is demonstrated in a wide range of operating current densities and chip dimensions varied from tens to hundreds of micrometers. It is shown that surface recombination, which is especially important in small‐size LEDs, is the major mechanism controlling evolution of the LED characteristics under the chip size variation. The impact of surface recombination on LED characteristics is predicted to weaken at high current densities typical for operation of micro‐LEDs due to shortening of carrier life time in the active region. Advantages of micro‐LEDs are discussed on the basis of the simulations.

Effect of Die Shape and Size on Performance of III-Nitride Micro-LEDs: A Modeling Study

“…Within the approach, the active region is simulated via (i) a relationship between the local density of current j crossing the active region, and p-n junction bias U, which is the electric potential drop between the lower and upper boundaries of the region, (ii) a dependence of the local internal quantum efficiency η i (IQE) on the current density j, and (iii) a current density dependence of sheet carrier concentration n 2D injected into the active region assumed to be nearly the same for electrons and holes. In order to obtain the LED structure characteristics j(U), η i (j), and n 2D (j), direct simulations can be applied [10], provided that temperature-dependent recombination coefficients are known with sufficient accuracy. Below, we will show how the above dependences can be extracted from characterization data of large-size LEDs, where the impact of surface recombination on LED characteristics is considered as negligible.…”

“…To optimize a µ-LED design, modeling and simulation of its operation is a powerful approach. Since µ-LEDs operate frequently at extremely high current densities, electrical, thermal, and optical phenomena become strongly coupled with each other, generally requiring joint 3D simulations [10]. A specific problem of such simulations is accurate accounting for temperature-dependent recombination coefficients related to non-radiative Shockley-Read-Hall (SRH), radiative, and Auger recombination, which is necessary for adequate prediction of thermal droop of the emission efficiency.…”

III‐Nitride Micro‐LEDs for Efficient Emissive Displays

“…If one uses traditional layered epitaxial structure and device fabrication processes, then the p-n junction will be exposed on the edge of the LED as shown in the inset of Figure 9 (grey sides), and surface recombination becomes a problem especially as the device becomes smaller. [191] Figure 9a shows the LED power conversion efficiency versus current density for the green LED with a square-shaped chip. A v s = 6 × 10 3 cm s −1 is assumed [146,192,193] which is found on m-plane bare surfaces and is the worst case.…”

P‐127: The Substrate Thickness Dependence on Micro LED Chip Arrays

“…The uniform color distribution over wide viewing angles can be a good trait for high quality display, and meanwhile, the uneven intensities among these colors can deteriorate the composite color at different angles and thus not favourable at all. However, previous studies and researches are mostly focused on the photoelectric and temperature characteristics of micro LEDs [7][8] [9]. Traditionally, the LED related simulation can also be focused on the extraction ratio of the emitted photons from the devices, and the patterned or AR coated surfaces can be really useful [10][11] [12].…”