Enhanced Performance Of Photonic-crystal GaN Light-emitting Diodes With Graphene Transparent Conducting Electrodes

With the great advantage of low energy consumption, environmentally friendly materials, light emitting diode(LED) is a semiconductor component of converting the electrical energy into the light energy. They have been widely used in various applications, such as full-color displays, general lighting, etc. It is considered as the fourth-generation light source of having the most potential to replace the traditional high-energy light sources. The GaN LED takes an important role in the LED devices and the material of GaN has become the mainstream of manufacturing LED device now. So far, indium tin oxide(ITO) has been widely used as transparent electrode in GaN LED. However, it is unstable in chemical solutions. In addition, it has a low transparency for ultraviolet range. What’s more, the price of the ITO has been increased for the scarce of indium. So, looking for the material to replace ITO as the transparent current spreading layer becomes necessary. Graphene(GR) has been used in photoelectric and optoelectronic devices for its excellent optical and electrical properties, but there are few reports about the use of graphene as the transparent conducting electrode in photonic crystal(PC) LED. This article is about the enhanced performance of PC GaN LED with graphene transparent electrodes. The main research contents of this paper are listed as follows,(1) In order to achieve the current spreading effect, the graphene is put on the PC structure as the transparent conducting electrode. The two-dimensional(2D) triangle-lattice air-hole PC GaN LED with double-layer graphene transparent electrodes(DGTE) have been designed and produced. Through the implementation, there were nine kinds of devices made, including the DGTE-PC LED, etc.(2) According to the relevant documents and constantly experiments, the key process of making the PC structure and the transfer of graphene was studied. The feasibility of each single process was verified. The steps and the parameters of the process were determined.(3) The current spreading effect of the double-layer graphene on the surface of the PC structure of the LED has been researched. Specially, we found that the part of the graphene suspending over the air hole of the PC structure was of much higher conductivity, which reduced the average sheet resistance of the graphene transparent conducting electrode and improved the current spreading of the PC LED. Therefore, the work voltage of the DGTE-PC LED was obviously decreased and the output power was greatly enhanced.(4) The COMSOL software was used to simulate the current density distribution of the samples. The results show that the etching of PC structure results in the degradation of the current spreading and that the graphene transparent conducting electrode can offer the uniform current spreading in the DGTE-PC LED.(5) After the completion of manufacturing of the devices, the device has been tested and analyzed, including the test and analysis of the transmission spectra of the current spreading layer, the device current spreading effect, the I-V characteristics of the devices and so on. The photoelectric and optoelectronic performance of the device was mainly researched.