Development of high brightness of the chip facing bottlenecks

Current, the further development of semiconductor lighting market requirements luminous efficiency of the blue LED highbay light to be rising, costs are declining. Cree LED chip based on silicon carbide has been achieved 200lm / w light efficiency production, R & D level of luminous efficiency can reach 276lm / w. LED chip costs down and enhance light efficiency race currently encountered several development bottleneck.

The blue chip exist Droop effect. Under the condition of a large current density, external quantum efficiency of the light emitting diode will decrease, tests showed Droop effect is caused by the Auger effect, including a variety of reasons, this effect limits the blue chip used in a large current density, thus hindering the decline in the cost of lumens.

The second is a green energy gap (Green GAP) and the energy gap in red (Red GAP). Wavelength from blue light into green band, the quantum efficiency of the LED will be decreased, such as 530nm green quantum efficiency drops quickly in a dark red spectrum; terms for red, the internal quantum efficiency can reach 100%, but the ideal white light source in the orange-red light emitting wavelength (e.g., 614nm), and its efficiency is decreased rapidly. These effects limit the green and red chip optical efficiency improvements, delaying a future generation of high-quality white. In addition, the efficiency of the green and yellow LEDs also by the impact of the polarization field, and this effect will become stronger with the higher concentration of indium atoms.

The third is the extension of heterogeneous growth problems. Since the epitaxial growth, crystal defects formed a large dislocation density and defect, resulting in the decline in luminous efficiency and lifetime decreased. Blue chip regardless of silicon carbide, sapphire, silicon substrate technology is heteroepitaxial, in the presence of lattice mismatch between the substrate and the epitaxial crystal dislocation, and also because the difference of the thermal expansion coefficient in the cooling process after epitaxial growth The thermal stress is generated, resulting in the epitaxial layer defects, cracks, wafer bending. Substrate directly affect the quality of the crystal quality of the epitaxial layer, thus affecting the efficiency and life. If for using GaN homogeneous substrate by epitaxial growth, using a non-polar, can minimize the defects of the active layer, so that the current density of the LED chips is 5-10 times higher than conventional chips, significantly improving luminous efficiency. Reportedly Seoul Semiconductor using the homogeneous substrate the development of nPola new products, compared with the current LED brightness in the same area five times higher, but the the GaN the homogeneity substrate for the LED is still too expensive.

Overall, in the future development of the blue LED highbay light, flip chip, high-voltage chips, silicon chips are the future trends. The flip chip good heat dissipation can increase the injection current, do not fight the lines can improve the reliability of the product in the application process; hypertension LED chip can more closely match the supply voltage to improve power conversion efficiency, plus custom IC power most suitable for LED bulb; silicon LED chip can be epitaxially grown on a 6-inch or 8-inch silicon substrate, can greatly reduce the cost of LED to accelerate the advent of the era of the semiconductor lighting applications. For other colors, the red LED chip and green LED chip light efficiency there is still much room for improvement, further enhance light efficiency with the red and green LED chips, white is not necessarily the Blu-ray The form of the LED chip and yellow phosphor RGB or other form of the future white package may change a lot.

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