GLOBAL-Promoting Research Partnership in Fabrication of Advanced III-nitride Optoelectronics With Ultra Energy Efficiency Using Nanotechnology

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Our research has the potential to meet two major challenges which human beings are facing: energy crisis and climate change. Currently, the energy consumed due to general illumination accounts for 29% of the world's total energy consumption. Although the energy provided by an hour of solar radiation on the Earth is equivalent to the world's total energy consumption per year, solar cells contribute only 0.03% to the figure. Therefore, it is necessary to develop new technologies to achieve ultra energy-efficient solid-state lighting sources and solar cells. The appearance of III-nitride semiconductors provides human beings with such a unique opportunity, as the light emission from III-nitrides covers the complete visible spectrum and also a major part of the solar spectrum. It has been predicted that III-nitride LEDs if used in our homes and offices could save 15% of the electricity generated at power stations, 15% of the fuel used, and 15% reduction in carbon emission.For more than a decade substantial efforts have been devoted to developing high-brightness III-nitride LEDs (HB-LEDs) worldwide. Consequently, major achievements have been made. However, a fatal problem has appeared, and has to be solved urgently. That is the well-known "efficiency droop": the efficiency of HB-LEDs shows the highest value only at a low injection current, and a further increase in injection current leads to a significant reduction in efficiency. This is the "efficiency droop". Under the injection current required for practical applications, the efficiency drops down to >50% of the peak value, meaning that a large amount of energy has been wasted. This also causes a severe reliability issue, as the wasted energy leads to an elevated temperature of the devices and thus severe degradation in device performance. The physical origins of the efficiency droop are very complicated and thus unclear. So far, there is not any efficient solution. In the project, the scientists from 6 world-leading teams at University of Sheffield, Yale University (USA), Nanjing University (China) and Technology University of Braunschweig (Germany) are pooling their unique but complementary expertise, proposing to employ a number of advanced nanotechnologies and epitaxial growth techniques in order to explore the fundamental issue, and then achieve ultra energy-efficient LEDs. For solar cells, it has been predicted that an energy-conversion efficiency of >50% can be achieved with III-nitrides, which is much higher than that of any current solar cell. The solar energy-conversion efficiency of current III-nitride solar cells is extremely low, only ~3% in the best report due to a number of technologic challenges. We will combine our complementary expertise from 6 teams to tackle the challenges by employing a similar nanotechnology to fabricate into nanorod array solar cells on the epiwafers with a thick super-lattice structure on the GaN substrates with ultra-high crystal quality.