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Abstract
We demonstrated two types of GaN-based flip-chip light-emitting diodes (FCLEDs) with distributed Bragg reflector (DBR) and without DBR to investigate the effect of dielectric TiO2/SiO2 DBR on optical and electrical characteristics of FCLEDs. The reflector consisting of two single TiO2/SiO2 DBR stacks optimized for different central wavelengths demonstrates a broader reflectance bandwidth and a less dependence of reflectance on the incident angle of light. As a result, the light output power (LOP) of FCLED with DBR shows 25.3% higher than that of FCLED without DBR at 150 mA. However, due to the better heat dissipation of FCLED without DBR, it was found that the light output saturation current shifted from 268 A/cm2 for FCLED with DBR to 296 A/cm2 for FCLED without DBR. We found that the use of via-hole-based n-type contacts can spread injection current uniformly over the entire active emitting region. Our study paves the way for application of DBR and via-hole-based n-type contact in high-efficiency FCLEDs.
Highlights
The wide bandgap GaN and related materials have been extensively studied and implemented for optoelectronic devices that emit light in the spectrum between ultraviolet and visible light [1,2,3,4,5,6,7]
We investigated the effect of dielectric TiO2/SiO2 distributed Bragg reflector (DBR) on the electrical and optical properties of flip-chip light-emitting diodes (LEDs) (FCLEDs)
We used the commercial software, TFCalc, to model the design of a conventional single DBR stack consisting of 14 pairs of TiO2/SiO2 dielectric layers optimized for central wavelength at 465 nm
Summary
The wide bandgap GaN and related materials have been extensively studied and implemented for optoelectronic devices that emit light in the spectrum between ultraviolet and visible light [1,2,3,4,5,6,7]. LEDs should be driven at a high current density to obtain higher light output power (LOP), which inevitably generates a large portion of heat [21]. The LEE of top-emitting LEDs was limited by the absorption of light by opaque metal electrodes and total internal reflection (TIR) of the generated light at the GaN (n = 2.45)/air (n = 1) interface resulting from their very different refractive indices [26,27,28,29]. FCLEDs are commonly bonded to a high thermal conductivity submount such as silicon, resulting in a superior heat dissipation capability and a higher light output saturation current density.
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