Gu et al. Nanoscale Research Letters 2011, 6:199 http://www.nanoscalereslett.com/content/6/1/199 original IQE is relatively low. A Si-on-insulator LED with higher efficiency rendered by Ag NPs has been reported by Pillai et al. [48]. By adopting a simple deposition process, an eightfold efficiency increase at 900 nm stemming from LEE enhancement is achieved. Although commercial all-Si laser diodes have not yet been made, there is great potential and much research is being conducted in this area. Conclusion Among the various techniques to improve the efficiency of LEDs, LSPR-based methods have great promise due to the high degree of enhancement and reasonable cost. The enhancement is generally attributed to the increase in the IQE or LEE of the device. By using traditional nanotechniques such as sputtering/deposition, EBL, and NSL, LEDs with a myriad of metallic NP geometries have been fabricated. By carefully examining their PL or EL properties, the enhancement mechanism has been elucidated, further confirming the immense potential of LSPR LEDs. One of the current tasks is to identify the suitable fabrication parameters and optimize the size and shape of the structure in order to achieve the best enhancing effect experimentally. Analytical expressions have been obtained for the interaction between simple nanostruc- tures like nanoholes and light [83]. More powerful are computer softwares, such as finite difference time domain [FDTD] tools, for it is flexible to simulate any structures with them, from regular to highly disor- dered. As a common practice in the emerging field of metamaterials such as sub-wavelength metallic struc- tures, it is routine to first simulate and examine the efficacy of the structures before actual fabrication and performance assessment [84-88]. Similarly here at opti- cal frequencies, simulated and measured electromag- netic waves near metallic NPs irradiated by light often agree well; for example, simulation results from nanos- caled antennae which can effectively enhance light emission have been reported [38,39]. As the gap between antennas in microwave engineering and those in optical frequencies is being bridged, nanoantenna structures are promising in further enhancing the LEE in a LED, especially OLED, in which the IQE of the device is already high and cannot be significantly increased. For an LED with a mediocre IQE, nanoan- tennae can possibly be used to accomplish both IQE and LEE enhancement. Another challenge lies in the fabrication techniques. That is, even though the struc- tures can be designed, they may not be produced using current technology. With regard to the fabrication challenges, efforts are expected to extend existing methods proven useful for arraying ordered metallic arrays such as nanoimprint and chemical synthesis to Page 10 of 12 LED fabrication. The key is to protect the LED struc- tures during chemical processing. Acknowledgements This work was jointly supported by the National Natural Science Foundation of China under grant no. 50801013 and no. 51071045; Natural Science Foundation of Jiangsu Province, China, under grant no. BK2009291; Specialized Research Fund for the Doctoral Program of Higher Education under grant no. 200802861065; Excellent Young Teachers Program of Southeast University; Hong Kong Research Grants Council (RGC) General Research Fund (GRF) no. CityU 112307; and City University of Hong Kong Strategic Research Grant (SRG) no. 7008009. Author details 1Department of Physics, Southeast University, Nanjing 211189, People’s Republic of China 2Current address: Chien-Shiung Wu College, Southeast University, Nanjing 211189, People’s Republic of China 3Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, People’s Republic of China Authors’ contributions XG reviewed literatures and drafted the manuscript. TQ and PKC participated in the manuscript drafting and provided constructive opinions in this review paper. WZ also helped to draft the manuscript. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 21 September 2010 Accepted: 8 March 2011 Published: 8 March 2011 References 1. Holonyak N, Bevacqua SF: Coherent (Visible) light emission from GaN (As1-xPx) junctions. Appl Phys Lett 1962, 1:82. 2. 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