Center for Nanoscale Characterization & Devices, Photonics for Energy Division

As one of the three primary color LED compositing white LED, red LED is broadly used in alarm, information display and traffic lighting system. Moreover, UV-free red light can avoid damage to plant by UV light and promote the plant photosynthesis. It can apply to plant cultivation in the controlled ecological life support system. Since the ZnO/GaN heterojunction LED usually emits UV light that derived from near-band-edge (NBE) radiative recombination of ZnO and/or GaN, it is worthy of tunning electroluminescence (EL) wavelength of ZnO/GaN p-n heterojunction LED from UV to UV-free red light.

Recent years, Professor Yihua Gao’s group in Wuhan National Laboratory for Optoelectronics and School of Physics has being devoted themselves to the optoelectronic devices based on one-dimensional ZnO nanomaterials. By using a one-step simple chemical vapor deposition method, the group fabricated a new red LED based on the cross-connected p-ZnO:Cu nanobushes/n-GaN heterojunction by doping Cu element in ZnO. The EL light of this LED is tuned from UV of ZnO/GaN to UV-free red by the electronic interfacial transition from the conduction band of n-GaN to the deep acceptor levels of p-ZnO:Cu. The EL measurement indicates that this LED emits stable UV-free red light of 677 nm and 745 nm. This research provides a new approach to fabricate red LEDs.

This work has been published in Optics Express (vol. 24, Issue 4, pp. 3940-3949, 2016, DOI:10.1364/OE.24.003940). This work was supported by the National Natural Science Foundation of China (11374110, 11074082,11204093,51371085,11304106,11104097). This work also received the help of Dr. Junbo Han and Yibo Han (Wuhan National High Magnetic Field Center), Dr. Jun Su, Dr. Luying Li and Dr. Nishuang Liu.

Fig. 1(a) Schematic diagram of the p-ZnO:Cu/n-GaN LED device. The circled inset part shows the schematic of the cross-connected nanobush structure. (b) The EL spectra of this device under different forward bias voltages. (c) Photo galleries of room temperature EL from the p-ZnO:Cu/n-GaN LED at the forward bias voltage from 10 V to 20 V. (d) Schematic energy band diagram of p-ZnO:Cu/n-GaN can  explain the red light emission in EL.