23 February 2018 Recent progress on GaN-based superluminescent light-emitting diodes in the visible range
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Abstract
Superluminescent light emitting diodes (SLEDs) have beam-like optical output similar to laser diodes (LDs) while offering a broader emission wavelength spectrum. They represent, therefore, an interesting alternative to conventional LDs for applications where a short coherence length or low speckle noise are required. Visible SLEDs emitting in the red, blue, and green are ideal candidates for the manufacturing of speckle-free light sources in portable or wearable compact projection systems. In this paper, we review the current status of EXALOS’ GaN-based SLED technology in the violet-blue spectral range and report on our recent progress in terms of performance for devices with 440-460 nm emission. Furthermore, we discuss the challenges in achieving light output at even longer wavelengths. As a matter of fact, lower refractive index contrast between the waveguiding and cladding layers, decreased p-type doping efficiency when growing at low temperatures, low crystal quality and thermal stability of the active region have to be addressed and solved in order to achieve green emission. The epitaxial structures were grown by metalorganic vapor phase epitaxy (MOVPE) on c-plane freestanding GaN substrates. Growth was followed by standard fabrication of SLEDs with a ridge waveguide design. A record CW output power of 150 mW (at an operating current of 330 mA) and a wall-plug efficiency (WPE) of 8% have been obtained at an emission wavelength >440 nm.
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A. Castiglia, A. Castiglia, M. Rossetti, M. Rossetti, M. Malinverni, M. Malinverni, C. Mounir, C. Mounir, N. Matuschek, N. Matuschek, M. Duelk, M. Duelk, C. Vélez, C. Vélez, } "Recent progress on GaN-based superluminescent light-emitting diodes in the visible range", Proc. SPIE 10532, Gallium Nitride Materials and Devices XIII, 105321X (23 February 2018); doi: 10.1117/12.2287763; https://doi.org/10.1117/12.2287763
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