1.4× efficiency improvement in transparent-substrate (AlxGa1−x)0.5In0.5P light-emitting diodes with thin (⩽2000 Å) active regions

Gardner, Nathan F.; Chui, H. C.; Chen, E. I.; Krames, Michael R.; Huang, James; Kish, F. A.; Stockman, S. A.; Kocot, Chris; Tan, Tun S.; Moll, N.

doi:10.1063/1.123810

Cited by 47 publications

(28 citation statements)

References 7 publications

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“…As a result, photon out-coupling from wave-guided modes into vertical radiation modes is enhanced during multiple round trips between surface and ODR. The external quantum efficiency of the ODR-LED is still smaller as compared to values of % for TS-LEDs operating at 630 or 650 nm [14], [15]. However, the TS-devices employ a very thick window layer ( 45 m) resulting in a better extraction efficiency as compared to the present ODR-LED with a 2-m-thick window.…”

Section: Experiments and Resultsmentioning

confidence: 76%

Omnidirectional reflective contacts for light-emitting diodes

Gessmann

Schubert

Graff

et al. 2003

IEEE Electron Device Lett.

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An electrically conductive omnidirectional reflector (ODR) is demonstrated in an AlGaInP light-emitting diode (LED). The ODR serves as p-type contact and comprises the semiconductor, a metal layer and an intermediate low-refractive index dielectric layer. The dielectric layer is perforated by an array of AuZn microcontacts thus enabling electrical conductivity. It is shown that the ODR significantly increases light extraction from an AlGaInP LED as compared to a reference LED employing a distributed Bragg reflector (DBR). External quantum efficiencies of 18% and 11% are obtained for the ODR-and the DBR-LED, respectively.

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Section: Experiments and Resultsmentioning

confidence: 76%

Omnidirectional reflective contacts for light-emitting diodes

Gessmann

Schubert

Graff

et al. 2003

IEEE Electron Device Lett.

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“…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 window layer were grown. The group sources used are trimethylaluminum(TMAl), trimethylgallium(TMGa) and trimethylindium(TMIn), and the group V are phosphine (PH 3 ), arsine (AsH 3 ) .…”

Section: Fig1 Simulated Reflected Spectra Of Dbrmentioning

confidence: 99%

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

Han

Deng

et al. 2007

Optoelectron. Lett.

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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

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“…2͒ and 75 mm wafers. 3 The external quantum efficiency ext of TS AlGaInP LEDs has been increased to record levels by reducing reabsorption of photons in thinner multiwell active layers, 4 and by shaping the chip into a truncated inverted pyramid to further increase light extraction efficiency. 5 LED lighting is valued for its long lifetimes and low power consumption relative to incandescent sources.…”

Section: Introductionmentioning

confidence: 99%

Evidence for voltage drops at misaligned wafer-bonded interfaces of AlGaInP light-emitting diodes by electrostatic force microscopy

O'Shea

Camras

Wynne

et al. 2001

Journal of Applied Physics

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Electrostatic force microscopy (EFM) with phase detection has been applied to cleaved cross sections of wafer-bonded transparent substrate (TS) AlGaInP light-emitting diode (LED) structures. EFM was performed with the LED under active bias to image the voltage drops across the device layers. Measurements on a nonwafer-bonded, absorbing substrate (AS) AlGaInP LED wafer, showed a voltage drop only at the p–n junction. A TS wafer with high forward voltage (Vf ) showed a much larger voltage drop at the wafer-bonded interface, compared with a normal TS LED wafer. Secondary ion mass spectrometry profiles of these wafers revealed ∼1×1013 cm−2 of carbon at the bonded interface in the high Vf sample, compared to ∼3×1012 cm−2 in the normal wafer. The unwanted voltage drop at the bonded interface was likely caused by a combination of carbon acting as a p-type dopant and the presence of interface states due to a ∼3° in-plane rotational misalignment at wafer bonding.

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1.4× efficiency improvement in transparent-substrate (AlxGa1−x)0.5In0.5P light-emitting diodes with thin (⩽2000 Å) active regions

Cited by 47 publications

References 7 publications

Omnidirectional reflective contacts for light-emitting diodes

Omnidirectional reflective contacts for light-emitting diodes

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

Evidence for voltage drops at misaligned wafer-bonded interfaces of AlGaInP light-emitting diodes by electrostatic force microscopy

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