OSRAM: LED technology through high current efficiency is not easy to drop UX:3"

Germany OSRAM Opto Semiconductors (OSRAM Opto Semiconductors GmbH) developed a new type of LED structure UX:3". The company said that the structure can not only greatly enhance the external quantum efficiency of the blue LED and other class LED GaN, but also can significantly inhibit the LED in large current through the decline in luminous efficiency of the recognized subject. The reduction in luminous efficiency can be suppressed by reducing the non radioactive recombination, which is not accompanied by luminescence. The day before, the reporter and the inhibitory effect of how to use UX:3 and other issues, interviewed OSRAM Opto Semiconductors Application Engineer Maekawa Keisuke and deputy manager of marketing company Glenn-Yves Plaine.

Reporter: UX:3 embedded in the LED chip n contact electrode, through the hole and N type GaN semiconductor layer for electrical connection. Why does this kind of electrode configuration or structure reduce Auger recombination?

OSRAM: the higher the current density of Auger recombination in the LED active layer is, the more significant. The structure of UX:3 has the effect of reducing the current density, which reduces the auger recombination.

Previously, the blue LED chip using the "ThinGaN" technology is set on the chip surface type n contact electrode. Specifically, is used for electrical pads connected from the outside is arranged at one end of the end of the four chip, and the connecting line of the electrode pads (grid) around the surface of the chip, which causes a current to flow through the whole chip. In fact, the current is not uniform across the chip surface, the chip surface, the closer the pad and the grid, the greater the flow of current, so there is a high current density of local area (Figure 1 left). This is because the farther away from the pad, the greater the impact of the grid wiring resistance. With the increase in the current of the chip, this trend will continue to increase, so that the luminous efficiency of the decline is obvious. The reason is that there is a significant Auger recombination in the region with high current density.

UX:3 LED chip inside the chip to the surface of the expansion of the N type contact layer. From the N type contact layer, the N type GaN type semiconducting layer on the surface of the chip is electrically connected through a plurality of through holes (when the chip size is 1mm square). As a result, the voltage can be uniformly applied to the N type semiconductor layer (GaN) on the surface of the chip (Figure 1). Due to the elimination of the current density of the higher portion of the cloth, it is possible to substantially reduce the Auger recombination significant region.

Because the n contact layer is arranged inside the chip, the light emitting from the active layer to the outside of the chip can not be blocked again. This will get 75 to 80% of the high light extraction efficiency.

Figure 1:LED section structure of the chip and the brightness distribution on the surface of LED chip. The left side of the original ThinGaN technology using the LED chip, the right side of the LED chip using UX:3 technology. UX:3 technology using LED chip, its brightness is more uniform.

Figure 2: UX:3 technology using white LED "OSLUX". Camera flash.

Reporter: in addition to changing the configuration and shape of the n contact layer, whether or not to take other measures?

OSRAM: also thickened as the active part of the light-emitting part. The occurrence probability of Auger recombination is proportional to the carrier density of the 3 order, so that the decrease of carrier density can reduce the occurrence of auger recombination. By increasing the active layer, the carrier density is decreased. The active layer is not simple thickening, but the doping amount, etc..

Reporter: how much can improve the luminous characteristics?

OSRAM: the use of UX:3 blue LED chip, the output power of the chip in the case of 1mm square 350mA current input is about 10% higher than ThinGaN. The more input current, the greater the gap between UX:3 and ThinGaN. Using this blue LED chip white LED, the luminous efficiency can reach 136lm/W.

The forward voltage (VF) is only 100mV. It can be said that this is one of the main reasons for luminous efficiency can be improved.

Reporter: how much will change the manufacturing process? Through the hole, the yield will drop significantly?

OSRAM: due to the increase in the process of setting the hole, so the manufacturing process will increase. However, each manufacturing process is not a special process, just use the previous manufacturing process can be optimized. However, the depth of the hole is hundreds of nm, the depth and width are relatively small, so it will not bring much impact on the yield.

Reporter: please talk about the future of the application plan.

OSRAM: UX:3 will be the evolution of the ThinGaN version, from the high current into the high-end blue LED, white LED and green LED began to use. First of all, the use of mobile phone camera flash products, and in 2010 for the general purpose of lighting products (Figure 2). 1mm square is currently intended to use UX:3 on a large chip, but after the technology is mature, there may be on the standard size of the chip using UX:3.