We present a new method of making a textured V-pit surface for improving the light extraction efficiency in GaNbased light-emitting diodes and compare it with the usual low-temperature method for p-GaN V-pits. Three types of GaNbased light-emitting diodes (LEDs) with surface V-pits in different densities and regions were grown by metal-organic chemical vapor deposition. We achieved the highest output power and lowest forward voltage values with the p-InGaN V-pit LED. The V-pits enhanced the light output power values by 1.45 times the values of the conventional LED owing to an enhancement of the light scattering probability and an effective reduction of Mg-acceptor activation energy. Moreover, this new technique effectively solved the higher forward voltage problem of the usual V-pit LED.
An interesting structure of GaN-based lightemitting diodes (LEDs) with different indium-tin-oxide (ITO) films deposited on naturally textured V-shaped pits (V-pits) is fabricated and studied. The sputtered ITO assists the textured surface to get a better contact and thus reduces the forward voltage. Moreover, the ITO films prepared by different methods can serve as graded-refractive-index antireflective coatings, which can enhance the performance of the V-pits LED further. The results show that the V-pits LED with two layers ITO films have a stronger light output power than the reference LED by 52.1% at 20 mA, and the forward voltage is only a little higher than the standard LED.
Tris (8-hydroxyquinolino) aluminum (Alq3) films and their chemical failure process are investigated using x-ray photoelectron spectroscopy. We make sure that the O 1s spectrum of the pristine Alq3 only has one component which is in contrast to the current controversy on this issue. Our experiments further indicate that the chemical failure process of Alq3 holds the critical role to understand this problem. The chemical failure process also shows the organic carbon contamination and the replacement reaction between Alq3 and water, ultimately resulted in the failure of the device. These fundamental results provide a basis understanding for future development of Alq3-based light emitting devices.
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