30-mW-Class High-Power and High-Efficiency Blue Semipolar ($10\bar{1}\bar{1}$) InGaN/GaN Light-Emitting Diodes Obtained by Backside Roughening Technique

The first 30-mW-class semipolar blue light-emitting diode (LED) on a free-standing ($10\bar{1}\bar{1}$) GaN substrate has been demonstrated by using microscale periodic backside structures. The light extraction efficiency and corresponding output power were greatly enhanced, by up to 2.8-fold (bare...

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Published inApplied physics express Vol. 3; no. 10; pp. 102101 - 102101-3
Main Authors Zhao, Yuji, Sonoda, Junichi, Pan, Chih-Chien, Brinkley, Stuart, Koslow, Ingrid, Fujito, Kenji, Ohta, Hiroaki, DenBaars, Steven P, Nakamura, Shuji
Format Journal Article
LanguageEnglish
Published The Japan Society of Applied Physics 01.10.2010
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Summary:The first 30-mW-class semipolar blue light-emitting diode (LED) on a free-standing ($10\bar{1}\bar{1}$) GaN substrate has been demonstrated by using microscale periodic backside structures. The light extraction efficiency and corresponding output power were greatly enhanced, by up to 2.8-fold (bare chip) compare with conventional devices. At a driving current of 20 mA, the LED showed an output power of 31.1 mW and an external quantum efficiency of 54.7%. Semipolar GaN LED technology is now comparable to commercial $c$-plane blue LED technology, not only in terms of internal material properties but also in terms of chip processing techniques.
Bibliography:(a) Schematic views of the semipolar ($10\bar{1}\bar{1}$) LED device with backside roughening structures. (b) SEM images of the backside of the GaN substrate before roughening and (c) after roughening, from a 10° tilted angle. (a) Dependence of light output power on the densities of the conical features patterned on the backside of the devices. (b) SEM images of the backside of the device with low density ($\rho = 5.8\times 10^{5}$ cm -2 ), (c) medium density ($\rho = 9.0\times 10^{5}$ cm -2 ), and (d) high density ($\rho = 1.6\times 10^{6}$ cm -2 ) of conical features (upper diameter $\phi = 3$ μm). Dependence of light output power on the size of the conical features patterned on the backside of the devices. Inset: Cross-sectional SEM image of the backside of the device, indicating a conical feature with an upper diameter of 3 μm. Simulation and experimental data on $\eta_{\text{extr}}$ enhancement vs (a) density and (b) size of the conical features. Light output power vs current ($L$--$I$) and external quantum efficiency vs current ($\mathrm{EQE}$--$I$) curves for a packaged ($10\bar{1}\bar{1}$) LED with backside roughening under pulsed conditions. Insets: Schematic graph (left) and optical micrograph (right) of a working blue LED using a transparent packaging method.
ISSN:1882-0778
1882-0786
DOI:10.1143/APEX.3.102101