Conventional gallium nitride (GaN) LED components are usually based on sapphire or silicon carbide (SiC) because the two materials have a good lattice matching with GaN, and the substrate is usually 2" or 4" in size. The industry has been working to develop GaN with more abundant silicon wafers (6" or larger) because silicon substrates can significantly reduce costs and can be fabricated on automated IC production lines. It is reasonable to estimate Traditionally, this substrate can save 80% of the cost. However, the problem with the silicon substrate is that there is a serious mechanical and thermal mismatch with GaN, which causes severe warpage of the wafer constituting the LED element and deterioration of the quality of the crystal material. Silicon-based GaN technology from Cambridge University's derivative company CamGan (acquired by Plessey in 2012) has now solved this mismatch and has been successfully applied to its wafer processing plant in Plymouth, UK. As a result, the industry's first low-cost, entry-level commercial silicon-based GaN LED is now on the market. The primary products are mainly for the indicator light and accent lighting market, with a luminous efficacy of 30-40 lm/W. GaN on Si Growth: Silicon-based GaN growth Mirror layer added: added mirror layer Wafer: Using Wafers Flip bonded wafer: flip-chip bonded wafer Substrate removal: substrate removal Metallisation and surface texturing: spraying metal layers and surface textures The use of silicon substrates to produce LEDs requires some process steps to overcome the silicon material absorption problems inherent in the architecture and to create efficient components. In the wafer processing process (shown in Figure 1), a vertical LED component is designed on a GaN architecture (6"-based silicon wafer grown by MOCVD. Next, a highly reflective contact is deposited and adhered. (The reflectivity is typically 95%) and then some metal layers are made to paste the wafer onto the replacement substrate. This is followed by a wire bond that is used in the casting of the solder layer with a conductive and thermally conductive fusible gold tin layer (re-melting temperature of about 280 ° C) along with other metal layers to serve as a carrier between the solder metal and the component or replacement. After the bonding wire is completed, the parent wafer is removed, and the seed layer for epitaxial growth of the GaN layer is exposed. The wafer is flipped for the next LED element patterning process. The metal coating is patterned on the wafer and placed over the barrier layer to minimize the amount of light-emitting area coverage. Most of the current is delivered by the top metal (usually 2m). Finally, photo-extraction patterning is performed and etched into the GaN layer (exposed to the back of the bonding wire) to remove the parent wafer. The final step is especially critical for remote phosphor applications because it enables illumination pattern control of blue LEDs. Since the reflectance index of GaN semiconductors is very high (the reflection index of 445 nm blue light is about 2.45), only a small amount of light escapes into free space. According to Snell's law, its narrow light escape cone is about 25°. If we assume that the light emitted inside the semiconductor has a uniform spatial distribution and the mirror reflection index is greater than 90%, then only 8% of the total light can escape from the top surface of the semiconductor, and the other is totally internal reflection limited to the inside, and finally Absorption of component materials. To improve light extraction, a simple design involving the coupling of a semiconductor to a large dome lens having a radius 1.5 times larger than the size of the semiconductor light-emitting region is employed. Ideally, the dome lens should be made of a material with a reflection index (n~2.45) similar to GaN, which allows more than 90% of the light to escape to free space. In reality, however, there are no materials that match the GaN reflectance index and are cost-effective and can be made into a dome lens. Therefore, LED manufacturers often switch to easily available epoxy or silicon materials with a reflection index of about 1.5. . However, the addition of a dome lens with a reflection index of 1.5 only resulted in a light extraction rate of 12%. To overcome the weak light extraction performance due to total internal reflection, it is necessary to optimize the optical path of the light to increase its likelihood of appearing within the escape cone. MARSHINE Hydraulic Compressor Feature:
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Figure 1: Vertical LED production flow chart.
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