Nonradiative recombination — critical in choosing quantum well number for InGaN/GaN light-emitting diodes

Qiu³

et al. 2021

Front. Phys.

On the same micro-LED display panel, LED pixels are always operated with high and low biased voltages simultaneously to show different brightness and colors. Thus, it is vitally important to understand the effect of the heat transmission between LEDs under high and low biased voltages. In this work, we design two different LED groups: Group A is two LEDs bonded together for heat transmission and Group B is two LEDs separated from each other. Then, the two LEDs are operated at one fixed and one tuned biased voltage respectively in each group in a vacuum chamber and the efficiency of the two groups is studied both experimentally and numerically. Here, our experimental results demonstrate that Group A exhibits a maximum improvement of 15.36% in optical output power compared with Group B. The underlying reason is that the wall-plug efficiency of the LED with a voltage lower than photon voltage (V < ℏω/q) is surprisingly enhanced by elevated temperature owing to the heat transmission by the LED under a high biased voltage in Group A. Our further study shows that in such a low voltage region the improvement in the efficiency is attributed to the enhanced carrier concentrations with elevated temperature. On the other hand, the LED in Group A under a high biased voltage further raises the overall efficiency by alleviating the thermal droop due to reduced temperature. Device temperature measurement and numerical calculation of radiative recombination under different temperatures further support the superior performance of Group A LEDs. Our research results can act as the research prototype to design the high-efficient LED arrays for better energy recycling and thermal control.

Section: Resultsmentioning

confidence: 99%

Efficiency Boosting by Thermal Harvesting in InGaN/GaN Light-Emitting Diodes

Qiu³

et al. 2021

Front. Phys.

“…For the 50 μm × 50 µm and 100 μm × 100 µm cases, with the in-plane stress further reducing, the effect of the indium incorporation is stronger than that of the QCSE suppression, so we see the wavelength redshift. However, this high concentration of indium not only makes the peak wavelength redshifted, but also introduces more defects (Johnson et al, 2004), which can be proved by the shift of EQE peak toward higher current (Zhang et al, 2015), as shown in Figure 2B. It has also been reported that point defects enhance the nonradiative recombination (Cao et al, 2003), which can be another reason for the lower output power and EQE for the 50 μm × 50 µm size when the current is smaller than 120 mA.…”

Section: Resultsmentioning

confidence: 93%

Strain-Reduced Micro-LEDs Grown Directly Using Partitioned Growth

et al. 2021

Front. Chem.

Self Cite

Strain-reduced micro-LEDs in 50 μm × 50 μm, 100 μm × 100 μm, 200 μm × 200 μm, 500 μm × 500 μm, and 1,000 μm × 1,000 μm sizes were grown on a patterned c-plane sapphire substrate using partitioned growth with the metal-organic chemical-vapor deposition (MOCVD) technique. The size effect on the optical properties and the indium concentration for the quantum wells were studied experimentally. Here, we revealed that the optical properties can be improved by decreasing the chip size (from 1,000 to 100 µm), which can correspondingly reduce the in-plane compressive stress. However, when the chip size is further reduced to 50 μm × 50 μm, the benefit of strain release is overridden by additional defects induced by the higher indium incorporation in the quantum wells and the efficiency of the device decreases. The underlying mechanisms of the changing output power are uncovered based on different methods of characterization. This work shows the rules of thumb to achieve optimal power performance for strain-reduced micro-LEDs through the proposed partitioned growth process.

“…This value of peak-efficiency current density is a signature of the QW quality and the nonradiative recombination in QWs, such that, a larger J peak denotes a worse QW quality and a higher nonradiative recombination. 17,18 Therefore, considering the undoped part of the last QB and the Mg memory effect that gives rise to the time delay during the Mg doping process, 19 the Mg diffusion into the QW can be suppressed, and thus the LED with the p-type doping at EBL þ 1 = 2 QB shares almost the same QW quality as that with p-type doping at EBL. However, the QW quality gets worse for those LEDs with Mg-doping at EBL þ QB, EBL þ QB þ QW, and EBL þ QB þ QW þ QB.…”

Section: à3mentioning

confidence: 99%

Investigation of p-type depletion doping for InGaN/GaN-based light-emitting diodes

Applied Physics Letters

Tan

et al. 2017

Self Cite

Due to the limitation of the hole injection, p-type doping is essential to improve the performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs). In this work, we propose and show a depletion-region Mg-doping method. Here we systematically analyze the effectiveness of different Mg-doping profiles ranging from the electron blocking layer to the active region. Numerical computations show that the Mg-doping decreases the valence band barrier for holes and thus enhances the hole transportation. The proposed depletion-region Mg-doping approach also increases the barrier height for electrons, which leads to a reduced electron overflow, while increasing the hole concentration in the p-GaN layer. Experimentally measured external quantum efficiency indicates that Mg-doping position is vitally important. The doping in or adjacent to the quantum well degrades the LED performance due to Mg diffusion, increasing the corresponding nonradiative recombination, which is well supported by the measured carrier lifetimes. The experimental results are well numerically reproduced by modifying the nonradiative recombination lifetimes, which further validate the effectiveness of our approach.