1 State Key Laboratory of Mechanical Transmission, Chongqing Key Laboratory of Soft Condensed Matter Physics and Smart Materials, College of Physics, Chongqing University, Chongqing 400044, China;
2 College of Software, Chongqing College of Electronic Engineering, Chongqing 401331, China;
3 College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 400047, China;
4 Chongqing Engineering Research Center of Graphene Film Manufacturing, Chongqing 401331, China;
5 College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, China
In order to reduce the Schottky barrier height and sheet resistance between graphene (Gr) and the p-GaN layers in GaN-based light-emitting diodes (LEDs), conductive transparent thin films with large work function are required to be inserted between Gr and p-GaN layers. In the present work, three kinds of transparent conductive oxide (TCO) zinc oxide (ZnO) films, Al-, Ga-, and In-doped ZnO (AZO, GZO, and IZO), are introduced as a bridge layer between Gr and p-GaN, respectively. The influence of different combinations of Gr/ZnO hybrid transparent conducting layers (TCLs) on the optical and thermal characteristics of the GaN-LED was investigated by the finite element method through COMSOL software. It is found that both the TCL transmittance and the surface temperature of the LED chip reduce with the increase in Gr and ZnO thickness. In order to get the transmittance of the Gr/ZnO hybrid TCL higher than 80%, the appropriate combination of Gr/ZnO compound electrode should be a single layer of Gr with ZnO no thicker than 400 nm (1L Gr/400-nm ZnO), 2L Gr/300-nm ZnO, 3L Gr/200-nm ZnO, or 4L Gr/100-nm ZnO. The LEDs with hybrid TCLs consisting of 1L Gr/300-nm AZO, 2L Gr/300-nm GZO, and 2L Gr/300-nm IZO have good performance, among which the one with 1L Gr/300-nm GZO has the best thermal property. Typically, the temperature of LEDs with 1L Gr/300-nm GZO hybrid TCLs will drop by about 7 K compared with that of the LEDs with a TCL without ZnO film.
Project supported by the National High Technology Research and Development Program of China (Grant No. 2015AA034801), the Foundation of the State Key Laboratory of Mechanical Transmission of Chongqing University, China (Grant Nos. SKLMT-ZZKT-2017M15 and SKLM-ZZKT-2015Z16), the National Natural Science Foundation of China (Grant Nos. 11544010, 11374359, 11304405, and 1155305), the Natural Science Foundation of Chongqing, China (Grant Nos. cstc2015jcyjA50035 and cstc2015jcyjA1660), the Fundamental Research Funds for the Central Universities, China (Grant Nos. 2018CDJDWL0011, 106112017CDJQJ328839, 106112016CDJZR288805, and 106112015CDJXY300002), and the Sharing Fund of Large-Scale Equipment of Chongqing University, China (Grant Nos. 201612150094, 201712150005, 201712150006, and 201712150010).
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