33, 0.33). Calculating the EL spectrum under the bias of 40 V, the EL intensity ratio (380:560:610 nm) was about 36:1:4, and point E represented emission of the LED. Hence,

in order to fabricate WLEDs, the EL intensity of InGaN should be enhanced. In other words, the internal quantum efficiency of the InGaN layers should be improved. Improving the crystalline PND-1186 purchase quality and increasing the carrier concentration of the p-InGaN and n-InGaN layers are the efficient ways to achieve higher internal quantum efficiency. Figure 4 CIE x and y chromaticity diagram. Furthermore, the EL spectrum under a reverse bias of 40 V is presented in Figure 5. It is much different from that under the forward biases. The EL spectra show a blue emission accompanied by a broad peak centered at 600 nm under forward biases, whereas two emissions (380 and 560 nm) appeared under reverse bias. click here Obviously, they are attributed MLN2238 concentration to ZnO and InGaN:Si, respectively. The EL mechanism

under reverse bias probably is the impact excitation [18]. Figure 5 EL spectrum of the ZnO/InGaN/GaN heterojunction LED under the reverse bias. Conclusions In conclusion, we have fabricated heterostructured ZnO/InGaN/GaN LEDs. The EL spectra under forward biases show a blue emission accompanied by a broad peak centered at 600 nm. The peak at 600 nm was deemed to be the combination of the emissions from Si-doped InGaN at 560 nm and Mg-doped InGaN at 610 nm. Counted with the CIE chromaticity diagram, white light can be observed in theory through the adjustment of the emission intensity ratio. Furthermore, a UV emission and an emission peak centered at 560 nm were observed very under reverse bias. This work provides a simple way using the emission from ZnO, Mg-doped InGaN, Si-doped InGaN, and p-GaN to obtain white light in theory. With the appropriate emission intensity ratio, ZnO/InGaN/GaN heterostructured LEDs have potential application in WLEDs. Acknowledgments This work is supported by the National Natural Science Foundation

of China (NSFC) under grant numbers 10904116, 11074192, 11175135, and J0830310, and by the foundation from CETC number 46 Research Institute. The authors would like to thank HH Huang and BR Li for their technical support. References 1. Woo JY, Kim KN, Jeong S, Han C-S: Thermal behavior of a quantum dot nanocomposite as a color converting material and its application to white LED. Nanotechnology 2010, 21:495704.CrossRef 2. Jang HS, Jeon DY: Yellow-emitting Sr3SiO5:Ce3+, Li+ phosphor for white-light-emitting diodes and yellow-light-emitting diodes. Appl Phys Lett 2007, 90:041906.CrossRef 3. Jang HS, Im WB, Lee DC, Jeon DY, Kim SS: Enhancement of red spectral emission intensity of Y3Al5O12:Ce3+ phosphor via Pr co-doping and Tb substitution for the application to white LEDs. J Lumin 2007, 126:371.CrossRef 4. Chung W, Park K, Yu HJ, Kim J, Chun B-H, Kim SH: White emission using mixtures of CdSe quantum dots and PMMA as a phosphor. Opt Mater 2010, 32:515.