Fabrication and property analysis of AIGaInP red light LED with high bright

Abstract

The AlGaInP quaternary alloy that is lattice matched with GaAs substrate has a direct band gap transition in the wavelength region between green and red, and therefore is the most important materials for visible LEDs. Though AlGaInP LEDs have been commercial used in outdoor displays and traffic lights [1,2] , many research efforts have still been made to increase the extraction efficiency. These efforts include growth of thick GaP window layer for current spreading and light extraction, and growth of distributed Bragg reflector (DBR under active region or using transparent substrate GaP to replace the absorbing GaAs substrate [3,4] .The reasons of influencing light extraction efficiency of LED are analyzed in this paper. On the base of simulation calculation, the LED with 20 pairs of Al 0.6 Ga 0.4 As/AlAs DBR, 12 m GaP window layer and enhancing transmission film were grown by MOCVD. At 20 mA injection current, the LED peak wavelength is 623 nm, the output light intensity on axis of this LED chip was 200 mcd, the output light power was 2.14 mW, and the external quantum efficiency is 5.4%.The reflectivity curves as function of wavelength were calculated using the optical transfer matrix method [5] . Fig.1 shows the simulated reflected spectra of different pairs of Al 0.6 Ga 0.4 As/AlAs DBR at 630 nm normal incidence. The reflectivities of 15 pairs, 20 pairs and 35 pairs of DBR are 73%, 87% and 99% respectively. The results of simulation indicate that for reaching 90% reflectivity the pairs of DBR should be more than 20.At LED surface growing an 1/4 wavelength enhancing transmission film (also called anti-reflective film) can effec-* The work is supported by Beijing Science and Technology Committee (D0404003040221) ** tively reduce reflection light. Fig. 2 shows the simulated transmissivity as function of the 1/4 wavelength anti-reflective film material refractive indexes. When there is no enhancing transmission film (refractive index is equal to 1) the transmissivity is 72%. The maximal transmissivity is 99% when the refractive index of anti-reflective film material is 1.8. Another method for increasing the output light efficiency is to grow thicker GaP window layer. In our experiment, a properly thicker GaP layer was applied. Fig.1 Simulated reflected spectra of DBRThe AlGaInP LED was grown by EMCORE D125 LP MOCVD. On a n-type (001) toward (111) direction 15 o GaAs substrates, a n-type Al 0.6 Ga 0.4 As/AlAs DBR, a 0.5 m n-type (Al 0.7 Ga 0.3 ) 0.5 In 0.5 P cladding layer, an (Al 0.1 Ga 0.9 ) 0.5 In 0.5 P/( Al 0. 5 Ga 0.5 ) 0.5 In 0.5 P multi-quantum well active regions [6] , a 0.5 m p-type (Al 0.7 Ga 0.3 ) 0.5 In 0.5 P cladding layer and a p-type GaP

Analysis of Junction Temperature of AlGaInP LED

“…AlGaInp can emit light from orange to red wavelengths by adjusting the content of Al and Ga in the LED material [8,9]. The layer materials of AlGaInP/GaInP MQW red LEDs is shown in Tab.…”