Light-extraction efficiency and forward voltage in GaN-based light-emitting diodes with different patterns of V-shaped pits

We present a new method of making a textured V-pit surface for improving the light extraction efficiency in GaN- based light-emitting diodes and compare it with the usual low-temperature method for p-GaN V-pits. Three types of GaNbased light-emitting diodes （LEDs） with surface V-pits in different densities and regions were grown by metal-organic chemical vapor deposition. We achieved the highest output power and lowest forward voltage values with the p-InGaN V-pit LED. The V-pits enhanced the light output power values by 1.45 times the values of the conventional LED owing to an enhancement of the light scattering probability and an effective reduction of Mg-acceptor activation energy. Moreover, this new technique effectively solved the higher forward voltage problem of the usual V-pit LED.

Overcoming the fundamental light-extraction efficiency limitations of deep ultraviolet light-emitting diodes by utilizing transverse-magnetic-dominant emission

While the demand for deep ultraviolet(DUV)light sources is rapidly growing,the efficiency of current AlGaN-based DUV light-emitting diodes(LEDs)remains very low due to their fundamentally limited light-extraction efficiency(LEE),calling for a novel LEE-enhancing approach to deliver a real breakthrough.Here,we propose sidewall emission-enhanced(SEE)DUV LEDs having multiple light-emitting mesa stripes to utilize inherently strong transverse-magnetic polarized light from the AlGaN active region and three-dimensional reflectors between the stripes.The SEE DUV LEDs show much enhanced light output power with a strongly upward-directed emission due to the exposed sidewall of the active region and Al-coated selective-area-grown n-type GaN micro-reflectors.The devices also show reduced operating voltage due to better n-type ohmic contact formed on the regrown n-GaN stripes when compared with conventional LEDs.Accordingly,the proposed approach simultaneously improves optical and electrical properties.In addition,strategies to further enhance the LEE up to the theoretical optimum value and control emission directionality are discussed.

Stably doped graphene transparent electrode with improved lightextraction for efficient flexible organic light-emitting diodes

Graphene-based flexible transparent electrodes(FTEs)are promising candidate materials for developing next-generation flexible organic light-emitting diodes(OLEDs).However,the quest for high-efficiency OLEDs is hindered by the low light-extraction and charge injection efficiencies of graphene electrode.Here,we combine the frustrated Lewis pair doping with nanostructure engineering to obtain high-performance graphene FTE.A p-type dopant aci-nitromethane-tris(pentafluorophenyl)borane(ANBCF)was synthesized and deposited on graphene FTE to form an aperiodic nanostructure,which not only improves the light-extraction but also stably p-dopes graphene to enhance its hole injection.The use of ANBCF-doped graphene as the anode enables high-efficiency flexible green OLEDs with external quantum efficiency(EQE)and power efficiency(PE)out-performing most flexible graphene OLEDs of comparable structure.This study provides a simple and effective pathway to fabricate high-performance graphene FTEs for efficient flexible OLEDs.