Recently, Taiwan National Cheng Kung University and Kunshan University of Science and Technology cooperated to insert a silicon dioxide/aluminum multilayer structure under the p-electrode of a nitride LED , and the optical power of the device was significantly improved. Here, silicon dioxide can improve the current spreading of the active region and reduce the current accumulation effect, and aluminum as a radiation mirror can reduce the absorption of light by the p-electrode and increase the extraction of the side light of the sapphire substrate. They compared three LEDs (common type as reference, silicon dioxide barrier LED, and silicon dioxide barrier + aluminum mirror LED). At 20 mA operating current, the use of silicon dioxide current barrier is more traditional. The power of the structural device increased by 15.7%, while the use of a silicon dioxide barrier + aluminum mirror increased the power by 25.8%. Most of the current nitride LEDs are epitaxially grown on an insulating sapphire substrate, so both the p-electrode and the n-electrode are on the same side of the sapphire, so that the metal electrode, especially the p-electrode near the active region, absorbs light. Reduced efficient extraction of LED light. If the absorption of light is reduced by reducing the thickness of the electrode, it will cause uneven current distribution, resulting in local high current density, generating a droop effect and reducing the efficiency of the LED. Therefore, the current expansion problem has become a key to the current efficiency of LED devices. The newly proposed reflective barrier structure of the National Cheng Kung University uses a silicon dioxide barrier + aluminum mirror, in which the reflectivity of the aluminum mirror to 430-480 nm blue light reaches 91%. This new structure not only improves current spreading, increases light extraction, but also reduces reverse leakage. The reverse leakage current at 5V is reduced from 33.2 nA in the conventional structure to 29.3 nA, which is the surface defect of silicon dioxide. Caused by the passivation effect. A small disadvantage of the new structure of the reflective barrier is that it reduces the contact area of ​​the p-GaN and ITO current spreading layers, which causes a slight increase in the operating voltage of the LED, which increases from 3.6V to 3.7V at 20mA. Four Burner Gas Cooker,Stainless Steel Gas Stove,Ce Table Outside Gas Cooker,4 Burner Glasstop Gas Cooker xunda science&technology group co.ltd , https://www.gasstove.be
Figure 1: Light output power / current contrast voltage (LIV) (black is the reference line, red is the normal blockage, green is the LED performance after blocking and reflection)
Figure 2: Diagram of the epitaxial structure of a nitride semiconductor
Figure 3: The bottom of the charge-coupled device with three LEDs at the bottom is the corresponding structure diagram