Charakterisierung interner optischer Verluste von Leuchtdioden im InGaN-Materialsystem mit Hilfe integrierter Wellenleiter (English shop)

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Efficient light-emitting diodes in the InGaN material system are highly attractive for generating light in the green to ultraviolet spectral range owing to numerous properties. The conversion of ultraviolet light by means of phosphors enables the generation of white light and thus the universal use of light-emitting diodes in lighting technology. Classical illuminants such as the incandescent bulb are already being surpassed in efficiency today. Nevertheless, the optimisation potential of the semiconductor chip has not yet been exhausted, since alongside high-quality epitaxial structures the problem of extracting the photons generated within the semiconductor has so far received little attention. Internal optical losses and the existence of total internal reflection prevent the light from leaving the semiconductor completely.

This work is concerned with a systematic approach to the internal optical losses that occur in sapphire- and silicon carbide-based light-emitting diode structures. An integrated optical waveguide experiment is used to investigate the lateral wave propagation of the light. The theoretical modelling of the particular, non-exponential intensity distribution provides insight into the absorption distribution, which is verified by means of further accompanying measurement techniques. A correlation between the absorption distribution and the layer structure leads to the finding that the defect-rich GaN existing between the sapphire substrate and the light-emitting diode structure acts as a strong absorber. For the first time, a quantitative analysis of the absorption properties is possible. By modifying the growth process, the absorption behaviour can be improved, thereby enabling an increase in the light output of the light-emitting diodes.