Contact persons:
Haiyan Ou| Building - 345A| Room-072| 45253782| haou@fotonik.dtu.dk
Abebe T. Tarekegne| Building - 345A| Room-079| 45253787| atil@fotonik.dtu.dk
Motivation: Solid state lighting based on LEDs is emerging as the most efficient alternative to the traditional fluorescent or incandescent lamps. The conventional LED-based white light sources have certain limitations such as the use of scarce rare-earth elements, the droop effect and constraints to achieve high color quality. In high power operations, these LED-based white light sources require expensive heat management and their efficiency decreases. These situations call for alternative light-emitting materials. Silicon carbide has excellent attributes which could minimize some of the limitations of LED-based white light sources and it is particularly suitable for high power white light emission. It has very high thermal conductivity and it is well known radiation resistant material which simplifies power management at high operations. It has large band gap with variations of bandgap depending on the polytype.
However, SiC sources need further investigation and engineering to improve their energy efficiency. Full understanding of the physics of the carrier-recombination dynamics and point defects is required. We are doing these investigations theoretically and experimentally including micro-photoluminescence measurements at cryogenic temperatures.
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Fig. 1. (a) Schematic sketch of a micro-photoluminescence setup that is used to investigate temperature-dependent PL emission in semiconductors. (b) Measured shift of PL spectrum at 66 K with change of excitation power. The inset shows the emission spectrum with excitation power of 3 mW over a wider spectral range.
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Task: The student will be part of an effort towards realizing an efficient photoluminescence emission in silicon carbide which involves several paths. In this particular project the focus will be investigation of the dependence of photoluminescence emission on the power of the excitation laser. To support the investigation and the physical understanding, temperature-dependent measurements with a micro-cryostat will be performed. The schematic of the micro-PL setup is shown in Fig. 1(a). Preliminary measurement results, that show shift of photoluminescence emission spectrum at temperature of 66 K in one of our samples (Al-N co-doped SiC), are shown in Fig. 1(b). The student will build on this by doing further measurements on different kinds of samples and measurement variables. Further analysis that involves measurement of photoluminescence decay time will be done.
Objectives: The objectives of the project can be bulleted as follows.
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Clarify the physical mechanisms of the power dependence of photoluminescence in silicon carbide.
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Evaluate the power dependence characteristics at several temperatures.
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Build correlation between the power dependent spectral characteristics with photoluminescence decay from time-resolved PL measurements.
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Set recommendations to improve emission efficiency based on the investigations.
More possibilities: We are working on several aspects of LED including new light emitting materials and characterization, modelling of non-equilibrium carrier dynamics, surface nano-structuring for light extraction improvement, nanoLED for visible light communication, high efficiency flip-chip UV LEDs etc. We can tailor a related project that suits your interest and qualifications. We encourage you to talk to us.