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8 March 2014 Gain saturation in InGaN superluminescent diodes
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The gain saturation is a crucial factor limiting achievable output power of superluminescent diodes (SLD), as it exponentially depends on optical gain value. Contrary to laser diodes, in SLDs gain is increasing with the increasing current even much above the transparency conditions. Therefore, SLDs provide us with an unique possibility to examine gain under high current densities (high carrier injection). In our work we examined SLDs fabricated in a “j-shape” ridge-waveguide geometry having chips of the length of 700 μm and 1000 μm, emitting in the blue-violet region. By comparing the amplified spontaneous emission measured along the device waveguide with true spontaneous emission measured in perpendicular direction, we are able to extract optical gain as a function of injected current. We show, that in our devices spontaneous emission exhibits a square-root-like dependence on current which is commonly associated with the presence of “droop” in case of nitride light emitting diodes. However, along the waveguide axis, fast processes of stimulated recombination dominate which eliminates the efficiency reduction. Calculated optical gain shows a substantial saturation for current densities above 8 kA/cm2.
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Anna Kafar, Szymon Stanczyk, Grzegorz Targowski, Tadek Suski, and Piotr Perlin "Gain saturation in InGaN superluminescent diodes", Proc. SPIE 8986, Gallium Nitride Materials and Devices IX, 89860P (8 March 2014);

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