![volume of triangular prism omni volume of triangular prism omni](https://i.pinimg.com/originals/9c/bb/04/9cbb04634d289c625c2d51ab736846c3.jpg)
More photons can escape from the top and bottom of the device, which was confirmed by numerically modeling light propagation within such device architecture. Furthermore, a significant enhancement in light extraction efficiency can be achieved from InGaN/AlGaN-based ultraviolet light-emitting diodes (UVLEDs) built on PSSA owing to the large refractive index contrast between the epilayers and PSSA. In comparison to conventional epilayers grown on patterned sapphire substrate (PSS), we observed a reduced threading dislocation density in the films grown on PSSA, attributing to the preferable vertical growth mode and reduced misfit at the coalescence boundary. Despite this, the nanostructure described in this work provides a readily realizable path to enhancing the light extraction efficiency of state-of-the-art deep ultra-violet light emitting diodes.Įpitaxially grown high crystalline quality InGaN/AlGaN multiple quantum structures on patterned sapphire with silica array (PSSA) have been successfully demonstrated. Consequently, the nanostructured p-contact should be combined with other optical strategies, such as nanopatterned sapphire substrates to increase the efficiency even further. While the nanostructure strongly decreases the light absorption in the p-contact, it is still not able to considerably reduce the total internal reflection. An optimum geometry of the nanostructure allows a light extraction efficiency of 15.0%, much higher than the typical 4.6% of a planar reference. This nanostructure reduces the absorption of the p-contact layer, leading to a higher emission into the n-contact compared to a planar reference. Here, we propose a structure consisting of a hexagonal periodic array of cylindrical nanoholes in the multi-layered p-contact which are filled with platinum. A contributing factor is the lower light extraction efficiency due to both highly absorbing p-contacts and total internal reflection. As a result, SiO2 layer with a thickness of over one wavelength is better, because the energy of evanescent wave decays to sufficiently negligible when it reaches the Al metal.ĭespite a wide array of applications, deep ultra-violet light emitting diodes offer relatively poor efficiencies compared to their optical counterparts. However, for the flip-chip LED on PSS, both the total internal reflection and the surface plasmon polariton resonance absorption play a major role leading to LEE increasing as the thickness of SiO2 layer increases.
![volume of triangular prism omni volume of triangular prism omni](https://i.ytimg.com/vi/Pqaxcjo3PiA/maxresdefault.jpg)
Therefore, the thickness of the p-GaN needs to satisfy even times of quarter wave and the thickness of SiO2 needs to be quarter wave.
![volume of triangular prism omni volume of triangular prism omni](https://scrn-cdn.omnicalculator.com/math/triangular-prism@2.png)
For the flip-chip LED on FSS, the LEE curve is oscillatory with changing the thickness of the SiO2 layer as a result of the coherent interference in the ODR and the optical cavity tuning effect for light source. Different design principles of ODR for the flip-chip LEDs on PSS and FSS are proposed to attain optimum LEE.
![volume of triangular prism omni volume of triangular prism omni](https://invbat.com/P33.png)
In this work, we investigate the effect of omni-directional reflectors (ODRs) on the light extraction efficiency (LEE) for flip-chip near-ultraviolet light-emitting diodes (NUV LEDs) on patterned (PSS) and flat sapphire substrate (FSS) using three-dimensional finite difference time-domain method.