Oct. 10, 2019, Nano Energy (IF:15.548) published a latest research paper titled “Monolithic integration of deep ultraviolet LED with a multiplicative photoelectric converter”. This work is a joint research accomplished by Prof. Changqing Chen, Prof. Yihua Gao and Prof. Jiangnan Dai from Huazhong University of Science and Technology, Prof. Zi-Hui Zhang from Hebei University of Technology and Prof. Haiding Sun from University of Science and Technology of China. It reported the first monolithic integration of deep ultraviolet LED with a multiplicative photoelectric converter to achieve a record high wall plug efficiency of 21.6%, which provided a novel approach to achieve highly-efficient DUV LEDs.
With respect to DUV LEDs, in lieu of the toxic mercury UV sources, they are promising for various prospects in medical phototherapy, sterilization and biomedical instrumentation system. However, their further applications are limited because of the low wall plug efficiency (WPE) in a single-digit percentage range. Particularly, the low carrier injection is an fundamental obstacle to achieve high WPE due to large Mg activation energy, low hole mobility and injection efficiency. Conventionally, electron blocking layer (EBL) has been implemented to enhance the hole injection and simultaneously suppress the electron overflow, meanwhile, tunnel junction was proposed to replace the p-AlGaN region and demonstrated effective carrier injection while eliminating the absorbing p-AlGaN and p-GaN layers. However, further improvement of hole injection efficiency will not be possible if the carrier recycling process is not involved until now.
Changqing Chen and Jiangnan Dai’ group established in Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology in 2008. Since the establishment of the group, the main research interest is focused on material and device developments of III-nitride based semiconductor LED. Systematically researches have been carried out on MOCVD epitaxy (Opt. Express. 26, 680-686, 2018; Appl. Phys. Lett. 114, 042101, 2019), chip design (ACS Photonics 5, 3534-3540, 2018; IEEE T. Electron. Dev. 66, 2997-3002, 2019), and device process (ACS Appl. Mater. Interfaces 9, 8238-8824, 2018; ACS Appl. Mater. Interfaces 11, 19623−19630, 2019) which lay a solid foundation of the research to achieve an efficient WPE for DUV LEDs.
Monolithic integration of two devices or functional configurations allows us to take advantage of the interaction between them and improve the performance of the device concerned. Substantially, the system-level innovation by enabling an integrated design environment and device ecosystem to realize ‘systems on a chip’ is accelerated in recent years. Changqing Chen and Jiangnan Dai’ group demonstrate a DUV LED integrated with a multiplicative photoelectric converter (MPC) that is composed of p-GaN/intrinsic GaN/n-GaN (p-i-n GaN) structure to induce the electric-optic conversion, thus considerably improve the hole injection efficiency, as shown in Fig. 1. This p-i-n GaN structure acts as hole-multiplier via firstly DUV light absorption and then electron-hole pair generation. The newly generated electron-hole pairs are firstly separated by the electric field in the p-i-n GaN structure so that multiple holes are driven into multiple quantum wells (MQWs), and finally contribute to the radiative recombination.
