Single chip white light emitting diode without fluorescent powder

The light emitting diode plays an important role in the solid state lighting project, will gradually replace the traditional lighting in the next 5-10 years, become a new source of energy saving and environmental protection. With the traditional light source (incandescent lamp, fluorescent lamp, halogen lamp, light emitting diode) has many advantages, such as long life, small volume, low power consumption, low pollution, high conversion efficiency, good applicability and safety etc.. With the development of the technology of GaN based V III- compound and the realization of the blue LED, people have been able to get the three color led. Usually, for white light emitting diodes are: 1) blue light emitting diode + yellow phosphor; 2) multi chip combination, the red, green, blue three die together; 3) photonic cycle to achieve white light; 4) the same substrates of different wavelength quantum well. The way. But the above way to obtain white light complex technology, high production costs, there are many difficulties to be overcome, so people have been committed to achieving these problems can avoid single chip white light emitting device, feasibility and predicts that the device from the theory. However, although the GaN based blue and green light-emitting diode technology is increasingly mature and commercialization, the realization of single chip white light emitting scientists dream. In 2006, the Chen Hong research group of the Institute of Physics (InGaN/GaN) used the stress modulation layer of InGaN to realize the stress modulation and control of the multi quantum well. The method does not need the phosphor and does not need to increase the complex control circuit. Under conventional injection current (20mA - 60mA), the color rendering index of white light is almost unchanged. Figure 1 shows the change in the color of the light under different injection currents. Figure 2 shows the cross section of the InGaN/GaN active region.

Figure 1 different injection current single chip white light emitting diode light-emitting photos: (a) 1 mA, (b), mA (c) 20 mA (d), mA ()

Figure 2 light emitting diode InGaN/GaN active area TEM

The photoluminescence spectra show that the LED emission of yellow light at low current. As the current increases more than 20mA, the blue light intensity increases gradually, and the exit light gradually changes from yellow to white. The cross section of transmission electron microscopy shows that a large number of In rich quantum dots are formed in the InGaN quantum well. When the injection current is low, the carrier is In rich QDs capture emit yellow light, with increased current, quantum dot quantum well region outside began to capture carriers, after radiation emitted blue, blue and yellow light mix to produce white light. The results of this study were published (Applied Physics Letters 91, 161912 (2007)), attracted international attention in the industry magazine compound semiconductor high degree of attention, were reported in the December 10, 2007 "Research Review" column.

The work was supported by the Ministry of science and technology and the National Natural Science Foundation of China

Source: Institute of physics, Chinese Academy of Sciences