Semi-polar GaN epitaxy for high frequency µLEDs

Semiconductor nitride-based LEDs have reached a high level of maturity due to their use in the field of lighting. While the internal electric field present in InGaN quantum wells does not limit the efficiency of blue LEDs, it does induce the confined quantum Stark effect (QCSE), which limits the bandwidth of the LEDs and thus their potential use in high-frequency optical communication. In this context, the thesis aim at controlling the MOCVD growth of InGaN/GaN epi-structures on SOI (Silicon on Insulator) along a semi-polar crystallographic orientation [10-11], which mitigates the adverse effects of QCSE. The epitaxy of GaN on SOI poses several challenges that need to be addressed to achieve the buffer quality required for µLED fabrication. These challenges include the chemical reactions between Ga and silicon and the difference in thermal expansion coefficients between GaN and silicon. This thesis will take place between CNRS-CRHEA in Valbonne, where growth conditions on small substrates will be optimized, and CEA-LETI in Grenoble, where the transfer to larger substrate formats (200mm) will occur. Understanding the growth mechanisms will be crucial for the success of this thesis, requiring in-depth structural characterization of the samples, for example, using electron microscopy or local probe techniques that provide atomic-scale characterization, as well as photo- and cathodo-luminescence techniques, etc. Finally, this thesis will involve participating in the design and performing the electro-optical characterization of µLEDs (micro LEDs) that will be fabricated in a cleanroom from the epitaxial structures developed on both small and large substrates. The goal of this part of the work is to optimize µLED performance and adapt the epitaxial LED structures to the semi-polar orientation.

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