• Rafailov, Edik U.
• Strassburg, Martin
• Zerova, Vera L.
• Yadav, Amit
• Zulonas, Modestas
• Titkov, Ilya E.
• Pietzonka, Ines
• Karpov, Sergey Yu.
• Lugauer, Hans-Juergen
• Galler, Bastian

Abstract

<p>Internal quantum efficiency (IQE) of a high-brightness blue LED has been evaluated from the external quantum efficiency measured as a function of current at room temperature. Processing the data with a novel evaluation procedure based on the ABC-model, we have determined separately IQE of the LED structure and light extraction efficiency (LEE) of UX:3 chip. <br/></p><p><br/></p><p>Full text <br/></p><p></p><p class="MsoNormal">Nowadays, understanding of LED efficiency behavior at high currents is quite critical to find ways for further improve­ment of III-nitride LED performance [1]. External quantum ef­ficiency <i style="mso-bidi-font-style:normal">η_e </i>(EQE) provides integral information on the recom­bination and photon emission processes in LEDs. Meanwhile EQE is the product of IQE <i style="mso-bidi-font-style:normal">η_i</i>and LEE <i style="mso-bidi-font-style:normal">η_ext</i> at negligible car­rier leakage from the active region. Separate determination of IQE and LEE would be much more helpful, providing correla­tion between these parameters and specific epi-structure and chip design. In this paper, we extend the approach of [2,3] to the whole range of the current/optical power variation, provid­ing an express tool for separate evaluation of IQE and LEE. <br/> We studied an InGaN-based LED fabricated by Osram OS. LED structure grown by MOCVD on sapphire substrate was processed as UX:3 chip and mounted into the Golden Dragon package without molding. EQE was measured with Labsphere CDS-600 spectrometer. Plotting EQE <i style="mso-bidi-font-style:normal">versus</i> output power <i style="mso-bidi-font-style:normal">P</i> and finding the power <i style="mso-bidi-font-style:normal">P_m</i> corresponding to EQE maximum <i style="mso-bidi-font-style:normal">η_m</i> enables comparing the measurements with the analytical rela­tionships <i style="mso-bidi-font-style:normal">η_i= Q/(Q+p^1/2+p^-1/2) ,p = P/P_m , </i>and<i style="mso-bidi-font-style:normal"> Q = B/(AC) ^1/2</i> where A, Band C are recombination constants [4]. As a result, maximum IQE value equal to QI(Q+2) can be found from the ratio <i style="mso-bidi-font-style:normal">η_m/η_e</i> plotted as a function of <i style="mso-bidi-font-style:normal">p^1/2+p1^-1/2</i> (see Fig.la) and then LEE calculated as <i style="mso-bidi-font-style:normal">η_ext</i> = <i style="mso-bidi-font-style:normal">η_m</i> <i style="mso-bidi-font-style:normal">(Q+2)/Q</i> . Experimental EQE as a function of normalized optical power <i style="mso-bidi-font-style:normal">p</i> is shown in Fig. 1 b along with the analytical approximation based on the ABC­model. The approximation fits perfectly the measurements in the range of the optical power (or operating current) variation by eight orders of magnitude. <br/> In conclusion, new express method for separate evaluation of IQE and LEE of III-nitride LEDs is suggested and applied to characterization of a high-brightness blue LED. With this method, we obtained LEE from the free chip surface to the air as 69.8% and IQE as 85.7% at the maximum and 65.2% at the operation current 350 rnA. </p><p class="MsoNormal">[I] G. Verzellesi, D. Saguatti, M. Meneghini, F. Bertazzi, M. Goano, G. Meneghesso, and E. Zanoni, "Efficiency droop in InGaN/GaN blue light-emitting diodes: Physical mechanisms and remedies," 1. AppL Phys., vol. 114, no. 7, pp. 071101, Aug., 2013. </p><p class="MsoNormal">[2] C. van Opdorp and G. W. 't Hooft, "Method for determining effective non radiative lifetime and leakage losses in double-heterostructure las­ers," 1. AppL Phys., vol. 52, no. 6, pp. 3827-3839, Feb., 1981. </p><p class="MsoNormal">[3] M. Meneghini, N. Trivellin, G. Meneghesso, E. Zanoni, U. Zehnder, and B. Hahn, "A combined electro-optical method for the determination of the recombination parameters in InGaN-based light-emitting diodes," 1. AppL Phys., vol. 106, no. II, pp. 114508, Dec., 2009. </p><p class="MsoNormal">[4] Qi Dai, Qifeng Shan, ling Wang, S. Chhajed, laehee Cho, E. F. Schubert, M. H. Crawford, D. D. Koleske, Min-Ho Kim, and Yongjo Park, "Carrier recombination mechanisms and efficiency droop in GalnN/GaN light-emitting diodes," App/. Phys. Leu., vol. 97, no. 13, pp. 133507, Sept., 2010. </p><p/>

Topics

• impedance spectroscopy
• surface
• extraction
• nitride
• laser absorption spectroscopy