High-performance Gan-based light-emitting diodes with a novel patterned SiO2/Al2O3 passivation layer
In the field of solid-state lighting, high-performance Gan-based leds, as promising light sources, have received extensive attention and have been widely applied in various light-emitting bands such as ultraviolet and visible light. Improving the light extraction efficiency of gan-based leds is an important prerequisite for their further promotion and application.
However, due to the existence of total reflection at the contact surface between the LED and the air, the current light extraction efficiency is still very low. Considering the refractive index difference between GaN and air, the critical Angle c for total reflection from the chip to the air is only 24.6° which in turn reflects most of the light back into the LED chip and is absorbed by the epitaxial layer and converted into heat, significantly reducing the light extraction efficiency. However, if the Angle of light emission is less than c, then the light emitted by the LED can freely enter the air. In view of this, some current studies aim to enhance the efficiency of light extraction by altering the optical circuits within devices. Common methods include: introducing distributed Bragg mirrors (DBRS), photonic crystal structures, patternized substrates, and surface passivation, etc.
In recent years, researchers have combined theory and experiments to study the influence of different types of surface passivation layers on the optical and electrical properties of leds. Among them, traditional Gan-based leds with SiO2 passivation layers have been widely applied. Chang et al. demonstrated that SiNx films prepared by electron cyclotron resonance chemical vapor deposition at room temperature can passivate gan-based leds. The experimental results show that SiONx prepared by the plasma-enhanced chemical vapor deposition (PECVD) method can be used as an anti-reflective passivation layer. To enhance the luminous intensity, Su et al. used hydrogen sulfide to passivate the surface of AlGaInP leds. So et al. observed that, under the condition of constant reflux temperature, the bottom diameter of the hemisphere increased with the increase of reflux time. With the help of lithography technology, we used HF to remove the passivation layer on the electrode surface without damaging the surface. The I-V curve and LOP measurement of the LED chip were accomplished by the FitTech IPT6000 LED chip/wafer test system, and the reverse leakage current IR was measured by the microwave probe station.
Figure 3(a) shows the I-V characteristics of leds with different structures, namely: 0-minute reflow patterned SiO2/Al2O3 passivation layer (sample A); 5 minutes reflux patterned SiO2/Al2O3 passivation layer (sample B); 7-minute reflux patterned SiO2/Al2O3 passivation layer (sample C); 9-minute reflux patterned SiO2/Al2O3 passivation layer (sample D); 11-minute reflux patterned SiO2/Al2O3 passivation layer (sample E); And the traditional SiO2 passivation layer (as a reference). Due to having the same epitaxial structure, the I-V characteristics of these six types of leds are almost the same. Under an input current of 60mA, the forward voltage is 3.1V for all of them. Figure 3(b) shows the photoluminescence (EL) characteristics of these leds with a peak wavelength of 460nm and a high output power of Sample D.
