Deep UV LEDs can be widely used in anti-virus, sterilization, printing and communication fields. The proposal of the International Minamata Convention promotes the full application of deep UV LEDs. However, commercial deep UV LEDs have a serious external quantum efficiency of less than 10%. Limits the application of deep UV LEDs.
AlN material quality is one of the core factors of deep UV LEDs. AlN thin films are mainly heteroepitaxially grown on c-sapphire, 6H-SiC and Si (111) substrates by metal organic chemical vapor deposition (MOCVD). AlN There is a large lattice mismatch and thermal mismatch between the substrate and the substrate, which causes greater stress and higher dislocation density in the epitaxial layer, which seriously reduces device performance.
At the same time, AlN precursors have higher migration barriers and poor wettability on such substrates, and tend to grow in three-dimensional islands. A certain thickness is required to achieve fusion, which increases the time cost.
Recently, the Lighting Research and Development Center of the Institute of Semiconductors of the Chinese Academy of Sciences has collaborated with the Peking University Nanochemistry Research Center and the Beijing Graphene Research Institute Liu Zhongfan's team to develop a new graphene / sapphire epitaxial substrate and propose a plasma pretreatment to modify graphene. A new strategy to promote the growth of AlN thin films to achieve deep UV LEDs.
DFT calculations show that the pyrrole nitrogen introduced into graphene by plasma pretreatment can effectively promote the nucleation growth of AlN films. High-quality AlN films can be obtained in a short period of time, which has low stress and low dislocation density, and deep UV LED devices show good device performance.
The achievement was published in Advanced Materials under the title of Improved Epitaxy of AlN Film for Deep-Ultraviolet Light-Emitting Diodes Enabled by Graphene (Adv. Mater., DOI: 10.1002 / adma.201807345). The researchers of the Institute of Semiconductors Li Jinmin, Wei Tongbo, Peking University Liu Zhongfan, and researcher Gao Peng are the co-corresponding authors of the paper. Chen Zhaolong and Liu Zhiqiang are the co-first authors of the paper.
At the same time, Wei Tongbo and Liu Zhongfan team proposed a graphene / NPSS nanographic substrate epitaxial AlN growth model. Theoretical calculations and experiments verified the enhanced metal atom migration on the graphene surface. Graphene reduced the merger time of AlN on NPSS by three minutes. Secondly, at the same time, the power of the deep ultraviolet LED has been significantly increased, so that the deep ultraviolet light source is expected to become a breakthrough in the industrialization of graphene.
The related results were selected as Featured articles after the publication of Appl. Phys. Lett. 114, 091107 (2019), and were specifically reported by AIPScilight under the title of New AlN film growth conditions enhance emission of deep ultraviolet LEDs. Semiconductor Magazine Edition (Issue 3, 2019) and Semiconductor Today feature a long story.
In addition, in response to the international technical problems of p-type doping in deep ultraviolet light-emitting devices, Liu Zhiqiang proposed a new mechanism of p-type doping in the defect resonance state. This method is based on energy band regulation to obtain an efficient acceptor ionization rate while maintaining a high The p-type gallium nitride conductivity of 0.16 Ω.cm is achieved, which lays the foundation for the subsequent application of graphene in transparent electrodes of deep ultraviolet devices.
Related results were published in Semicond. Sci. Technol. 33, 114004 (2018), and won the 2018 Young Scientist Best Paper Award of the journal. The results were also positively evaluated by the 2014 Nobel Prize in Physics, Amano.
The above series of research work was supported by the National Key Research and Development Plan, the National Natural Science Foundation of China, and the Beijing Natural Science Foundation.
source | Institute of Semiconductors, Chinese Academy of Sciences