The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extractio...The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extraction efficiency for LEDs with microsphere arrays was investigated by focusing on the effect of the packing density,packing configuration, and diameter-to-period ratio. The comparison studies revealed the importance of having a hexagonal and close-packed monolayer microsphere array configuration for achieving optimum extraction efficiency, which translated into a 3.6-fold enhancement in light extraction compared to that for a planar LED. This improvement is attributed to the reduced Fresnel reflection and enlarged light escape cone. The engineering of the far-field radiation patterns was also demonstrated by tuning the packing density and packing configuration of the microsphere arrays.展开更多
Near-infrared electroluminescence of InGaN quantum dots(QDs)formed by controlled growth on photoelectrochemical(PEC)etched QD templates is demonstrated.The QD template consists of PEC InGaN QDs with high density and c...Near-infrared electroluminescence of InGaN quantum dots(QDs)formed by controlled growth on photoelectrochemical(PEC)etched QD templates is demonstrated.The QD template consists of PEC InGaN QDs with high density and controlled sizes,an AlGaN capping layer to protect the QDs,and a GaN barrier layer to planarize the surface.Scanning transmission electron microscopy(STEM)of Stranski-Krastanov(SK)growth on the QD template shows high-In-content InGaN QDs that align vertically to the PEC QDs due to localized strain.A highAl-content A1_(0.9)Ga_(0.1)N capping layer prevents the collapse of the SK QDs due to intermixing or decomposition during higher temperature GaN growth as verified by STEM.Growth of low-temperature(830℃)p-type layers is used to complete the p-n junction and further ensure QD integrity.Finally,electroluminescence shows a significant wavelength shift(800 nm to 500 nm),caused by the SK QDs’tall height,high In content,and strong polarization-induced electric fields.展开更多
基金the U.S. Department of Energy (Grant No. NE TL, DE-PS26-08NT00290)in part by the National Science Foundation (ECCS-1408051, CBET1120399)
文摘The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extraction efficiency for LEDs with microsphere arrays was investigated by focusing on the effect of the packing density,packing configuration, and diameter-to-period ratio. The comparison studies revealed the importance of having a hexagonal and close-packed monolayer microsphere array configuration for achieving optimum extraction efficiency, which translated into a 3.6-fold enhancement in light extraction compared to that for a planar LED. This improvement is attributed to the reduced Fresnel reflection and enlarged light escape cone. The engineering of the far-field radiation patterns was also demonstrated by tuning the packing density and packing configuration of the microsphere arrays.
文摘Near-infrared electroluminescence of InGaN quantum dots(QDs)formed by controlled growth on photoelectrochemical(PEC)etched QD templates is demonstrated.The QD template consists of PEC InGaN QDs with high density and controlled sizes,an AlGaN capping layer to protect the QDs,and a GaN barrier layer to planarize the surface.Scanning transmission electron microscopy(STEM)of Stranski-Krastanov(SK)growth on the QD template shows high-In-content InGaN QDs that align vertically to the PEC QDs due to localized strain.A highAl-content A1_(0.9)Ga_(0.1)N capping layer prevents the collapse of the SK QDs due to intermixing or decomposition during higher temperature GaN growth as verified by STEM.Growth of low-temperature(830℃)p-type layers is used to complete the p-n junction and further ensure QD integrity.Finally,electroluminescence shows a significant wavelength shift(800 nm to 500 nm),caused by the SK QDs’tall height,high In content,and strong polarization-induced electric fields.
