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Generated carrier dynamics in V-pit enhanced InGaN/GaN light emitting diode

Ajia, Idris. A. and Edwards, Paul R. and Pak, Yusin and Belekov, Ermek and Roldan, Manuel A. and Wei, Nini and Liu, Zhiqiang and Martin, Robert W. and Roqan, Iman S. (2018) Generated carrier dynamics in V-pit enhanced InGaN/GaN light emitting diode. ACS Photonics, 5 (3). pp. 820-826. ISSN 2330-4022

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Abstract

We investigate the effects of V-pits on the optical properties of a state-of-the art highly efficient, blue InGaN/GaN multi-quantum-well (MQW) light emitting diode (LED) with high internal quantum efficiency (IQE) of > 80%. The LED is structurally enhanced by incorporating pre-MQW InGaN strain relief layer with low InN content and patterned sapphire substrate. For comparison, a conventional (unenhanced) InGaN/GaN MQW LED (with IQE of 46%) grown under similar conditions was subjected to the same measurements. Scanning transmission electron microscopy (STEM) reveals the absence of V-pits in the unenhanced LED, whereas in the enhanced LED, V-pits with {10-11} facets, emerging from threading dislocations (TDs) were prominent. Cathodoluminescence mapping reveals the luminescence properties near the V-pits, showing that the formation of V-pit defects can encourage the growth of defect-neutralizing barriers around TD defect states. The diminished contribution of TDs in the MQWs allows indium-rich localization sites to act as efficient recombination centers. Photoluminescence and time-resolved spectroscopy measurements suggest that the V-pits play a significant role in the generated carrier rate and droop mechanism, showing that the quantum confined Stark effect is suppressed at low generated carrier density, after which the carrier dynamics and droop are governed by the carrier overflow effect.