Highly efficient GaN-based cascaded LEDs
Final Report Abstract
The aim of the project was to use cascaded LEDs to increase the efficiency of LEDs at high input powers. GaN:Mg/GaN:Ge tunnel junctions have been successfully applied for vertical cascading of LED structures. The crystallographic properties of the active zones are not changed by the overgrowth. However, the biggest challenge turned out to be a degradation of the electrical and optical properties of the lower LED sections when overgrown with subsequent LED sections, due to Mg diffusion and hydrogen-induced repassivation of the buried p-GaN layers. Reducing the growth temperature and process time during overgrowth, as well as subsequent thermal activation, were identified as key strategies to improve the electrical and optical properties of the lower sections and need to be further investigated. The results of the project show that very good performance of cascaded LEDs is possible with optimized growth conditions and activation processes. Two-color LED structures have also been produced for the first time, opening up potential for RGB LEDs.
Publications
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Heavily Ge-doped GaN as transparent current spreading layer for blue tunnel junction light emitting diodes. Journal of Applied Physics, 132(23).
Berger, C.; Neugebauer, S.; Hörich, F.; Dadgar, A. & Strittmatter, A.
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“Heavily Ge-doped GaN films - properties and applications” International Conference on Metalorganic Vapor Phase Epitaxy (ICMOVPE XX) - Stuttgart
C. Berger, S. Neugebauer, A. Dadgar, H.Schürmann, J. Bläsing, P. Veit, J Christen & A. Strittmatter
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“MOVPE-grown optoelectronic devices based on GaN:Mg/GaN:Ge tunnel junctions” Int. Workshop on Nitride Semiconductors - Berlin, 2022 S. 711
C. Berger, A. Dadgar, J. Bläsing, G. Schmidt, H. Schürmann, P. Veit, J. Christen & A. Strittmatter
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“MOVPE-grown optoelectronic devices with GaN:Mg/GaN:Ge tunnel junctions” DPG Frühjahrstagung – Regensburg, 2022
C. Berger, A. Dadgar, J. Bläsing, G. Schmidt, H. Schürmann, P. Veit, F. Bertram, J. Christen & A. Strittmatter
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„Cascaded LEDs with GaN:Mg/GaN:Ge tunnel junctions“ DGKK/DEMBE Workshop – Bremen
C. Berger, A. Dadgar, H. Schürmann, G. Schmidt, J. Bläsing, J. Christen & A. Strittmatter
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Advanced cathodoluminescence microscopy of a cascaded InGaN/GaN LED” 65th Electronics Material Conference – Santa Barbara
G. Schmidt, F. Bertram, P. Veit, K. Wein, J. Christen, C. Berger, J. Bläsing, A. Dadgar & A. Strittmatter
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“Highly doped GaN:Ge/GaN:Mg tunnel junctions for novel GaN- based optoelectronic devices” DPG Frühjahrstagung – Dresden
C. Berger, A. Dadgar & A. Strittmatter
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„Optical Nano-Charakterization of a Cascaded InGaN/GaN LED“ 14th International Conference on Nitride Semiconductors – Fukuoka
F. Bertram, G. Schmidt, P. Veit, C. Berger, A. Dadgar, A. Strittmatter & J. Christen
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“Impact of overgrowth conditions on characteristics of tunneljunction LEDs” DPG Frühjahrstagung – Berlin
C. Berger, A. Dadgar & A. Strittmatter
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“Large area blue cascaded LEDs with GaN:Ge/GaN:Mg tunnel junctions grown by MOVPE” International Conference on Metalorganic Vapor Phase Epitaxy (ICMOVPE XXI) – Las Vegas
C. Berger, A. Dadgar & A. Strittmatter
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„Challenges of Mg acceptor diffusion and activation during MOVPE of cascaded LEDs with GaN:Ge/GaN:Mg tunnel junctions” DGKK/DEMBE Workshop – Berlin
C. Berger, A. Dadgar, G. Schmidt, K. Wein, F. Bertram, J. Christen & A. Strittmatter
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„Diffusion and activation challenges of Mg acceptors during growth of cascaded LEDs with GaN:Ge/GaN:Mg tunnel junctions by MOVPE” International Workshop on Nitride Semiconductor – Hawaii
C. Berger, A. Dadgar, G. Schmidt, F. Bertram, J. Christen & A. Strittmatter
