【Domestic News】Co-Doping is Expected to Achieve Ultra-Efficient White Ga₂O₃ LEDs

  Ga₂O₃ LED containing rare earth ions has high color rendering index and avoids the loss related to Stokes shift.

  Today's white LED has achieved great success. But it could not cover its weaknesses. Its common structure is the combination of yellow phosphor and blue light-emitting chip, resulting in some disadvantages, including low color rendering index, Stokes energy conversion loss and low thermal stability. The conversion from phosphor to rare earth ions is supposed to eliminate these shortcomings.

  Recently, a team from Saga University has achieved success in this area. The team is developing Ga₂O₃ LEDs co-doped with tantalum, europium and other elements. Guo Qixin, the spokesman of the team, told the reporter that in their co-doped LED, whose nature of the energy transfer mechanism of the red, green and blue mixed emission, needs further study. However, due to the Stokes shift, there is no energy loss. "The team's latest emission device is based on the previous Ga₂O₃ LEDs with rare earth ions.

  As early as 2021, Guo and his colleagues reported that a white LED consists of a vertical stack with 150 cycles and is composed of Ga₂O₃ thin films doped with tantalum, europium or erbium. Since the production of such multi-layer LED requires a complex deposition process, the team has begun to study the feasibility of controllable color LEDs based on co-doped tantalum, erbium and europium. Their device is hetero co-doped Ga₂O₃ based on p-type GaAs substrate, with a threshold voltage of about 9V, and emits color electroluminescence ".

  In order to prepare the devices, Guo and his colleagues used pulsed laser deposition technology to grow Ta, Er or Eu co-doped Ga₂O₃ films on p-type GaAs (111). The deposition temperature was 500 ℃, the oxygen atmosphere was 0.1 Pa, the growth time was 3 hours, and the distance between the substrate and the target was 40 nm. "Laser deposition is suitable for basic research," he added, “ as well as large-scale production of MOCVD. The LED structure was carefully characterized by X-ray diffraction, and the Raman spectrum analysis results showed that the Ga₂O₃-doped film is polycrystalline. When measuring the device, a layer of ITO film with a thickness of 250 nm was sputtered on the Ga₂O₃ surface, and a Au coating was deposited on the back by electron beam evaporation method. No emission was observed under reverse bias voltage, indicating that the device can work only by injecting electrons and holes. As to the combination of tantalum, erbium and europium ions, Guo said, it is the best dopant for manufacturing white LED, producing emission sharp peaks at 460 nm, 530 nm and 610 nm respectively. This causes the bright and uniform pink light to gradually change color with the driving current.

  According to the team, the white LED can be realized by fine-tuning the doping of tantalum, erbium and europium in the existing rare earth ion combination. One of the advantages of co-doped Ga₂O₃ LED is that its emission wavelength will not change with the ambient temperature. Guo and his colleagues are still studying the efficiency and life span of LEG. At the same time, they will reveal the energy transfer mechanism of co-doped Ga₂O₃ films by the low-temperature photoluminescence.

Reference

Huang et al. Appl. Phys. Express 15 081005 (2022)