Abstract
For high-power applications, it is important to improve the light extraction efficiency and light output of the vertical direction of LEDs. Flip-chip LEDs (FCLEDs) with an Ag/SiO2/distributed Bragg reflector/SiO2 composite reflection micro structure (CRS) were fabricated. Compared with the normal Ag-based FCLEDs, the light output power of the CRS-FCLEDs was increased by 6.3% at an operational current of 1500 mA, with the corresponding external quantum efficiency improved by 6.0%. Further investigation proved that the CRS structure exhibited higher reflectance compared with the commonly used Ag-mirror reflective structure, which originates from the increased reflective area in the sidewall and partial area of the n-GaN contact orifices. It exhibited markedly smaller optical degradation and thus higher device reliability as compared to normal Ag-based FCLED. Moreover, the light emission intensity distributions and far-field angular light emission measurements show that the CRS-FCLED has a strengthened light output in the vertical direction, which shows great potential for applications in high-power fields, such as headlamps for automobiles.
Highlights
With the development of semiconductor materials and packaging technology, the luminous flux of high-power white LEDs has rapidly improved
Contact orifices and n-GaN contact orifices were fabricated by inductively coupled plasma (ICP) etching with a CF4 /O2 gas mixture as the etching gas source [Figure 1b]
Results and Discussion fabricated by ICP etching with a CF4/O2 gas mixture as the etching gas source; (c) an AuSn alloy solder layer was deposited by thermal evaporation
Summary
With the development of semiconductor materials and packaging technology, the luminous flux of high-power white LEDs has rapidly improved. The application of LEDs in the automotive lighting field has gradually expanded, from signal indicators to current automotive headlights, reflecting the development trend that LEDs will become the mainstream light source in this field [1,2,3,4]. High power LED lighting generally requires high current density and vertical light extraction efficiency owing to the dense packaging [8,9,10]. External quantum efficiency (EQE) is the ratio between the number of electrically injected carriers and externally observed photons. Internal Quantum Efficiency (IQE) is the ratio between the electrically injected carriers and the internally emitted photons. It mainly depends on the carrier injection efficiency and the compound efficiency of quantum well [13]
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