Thin nitride LED substrate can improve the green LED light effect

Korea and Egypt researchers using wafer thinning (thinning) technology to improve the efficiency of nitride semiconductor LED. Participating organizations including Korea, Chonnam National University, Beni Sue Vee J University in Egypt and South Korea photonics technology research institute.

thinning effect is to reduce the residual nitride semiconductor structure stress (residual compressive stress), the stress impact effect on the pressure drop of the electric field in the LED framework. Between GaN and sapphire different coefficients of thermal expansion stress devices made of, in the epitaxial growth process after cooling would produce compressive stress.

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field effect will reduce the likelihood of electron hole recombination to generate photon. Component in the high indium (more than 20%) of indium gallium nitride (InGaN) alloy is more serious, and this kind of alloy is the green LED required. The current efficiency of the blue light InGaN LED was 50%, and the efficiency is high indium content of green LED is usually less than 10%.

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LED architecture (Figure 1) the growth of MOCVD on C 2 inch sapphire substrate. The substrate thickness is 430μ m, and integrate into 240&mu using traditional techniques; m x 600μ LED chip of M.

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substrate thinning technology through the use of grinding and polishing to achieve soft. These processes are used to minimize the damage of thinning process. In the thinned, cut into a single chip, n GaN contact layer of the wafer warpage and residual stress measurements show that, when the wafer is thinned to 200μ m and 80μ m, the warpage increased, stress reduction.

20mA injection current electroluminescence spectra show that, along with the current density in the substrate thinning increased. At the same time, 200μ m and 80μ the peak position of M substrate thickness respectively from 520.1nm (2.38eV) to 515.7nm (2.40eV) drift. The researchers explained: “ these findings clearly show that the silicon wafer warpage caused by mechanical stress will change the InGaN/GaN MQW active region of the piezoelectric field, and can be modified to bring value. But, blue light peak wavelength and the energy of the drift due to the band gap of the upgrade, the band gap of the ascension is because the electric field of InGaN/GaN MQW reduced pressure. ”

substrate thinning also enhance the internal quantum efficiency (IQE) and optical output power, but not to reduce current and voltage behavior. 20mA, substrate thickness from 200&mu to 80μ m; m, the light output power from 7.8mW to 11.5mW. This shows again that can reduce the piezoelectric field performance. The case of 20mA, different substrate thickness (200μ m, 170μ m, 140μ m, 110μ m, 80μ m) of forward voltage almost constant in 3.4V.