Résumé
Development of a reliable, selective, sensitive, technique for atmospheric trace gas concentrations monitoring is a critical challenge in science and engineering. Tunable single-frequency laser in the 2.3 to 3.3µm wavelength range, working in a continuous regime at room temperature can be used for absorption spectroscopy to identify and quantify several gases such as methane (greenhouse gases) and ethylene (food-processing) which are studied in the IES. We report here on the design and fabrication of 1st to 4th order distributed-feedback (DFB) antimonide-lasers diodes in the 2.3 to 3.3µm wavelength range. This process is applied to all studied structures grown by molecular beam epitaxy (MBE) on GaSb substrate. Electromagnetic modeling helps us to determine the Bragg grating period as well as the global geometry of the structure in order to optimize both modal discrimination and optical power of the lasing mode. The grating is defined by holographic lithography. Two DFB laser diode designs are proposed and investigated in parallel: -Side wall corrugation DFB: A corrugation on the lateral sides of the ridge waveguide is transferred by both wet and dry on a hard mask followed by a Cl2/N2 dry etching in the III-V heterostructure. -Buried DFB: The MBE growth is stopped at the top of the active region. Then the Bragg grating is etched by Ar sputtering . A MBE regrowth process is performed allowing the growth of the upper cladding layer. Next chemical etching of the mesa is done with fluoro-chromic acid. Si3N4 isolation and evaporation of ohmic contacts ends those processes. Finally we will show the results on the fabrication and characterization of the devices. This work is supported by the ANR NexCILAS international project, ANR MIDAS project, NUMEV labex and RENATECH national Network.