Optical refractive index measurements of AlGaAs at high temperature for fully automated molecular beam epitaxy growth of Bragg mirrors

Abstract In-situ measurement is a key feature to better understand and precisely control the growth of complex structures, such asvertical-cavity surface-emitting lasers (VCSELs). In this work, we are showing the precise measurement of optical indices of AlGaAs at 600°C over a wide spectral range (450 – 1400 nm). To do so, in-situ spectral reflectance measurement is used, combined with ex-situ layer thickness and composition measurement by X-ray diffraction enabling for precise determination of the optical indices with an accuracy better than 1%. To validate our measurements, we realized the complete automation of the growth of a GaAs/AlAs 940-nm-DBR by molecular beam epitaxy, without the need to pre-calibrate cells fluxes. The fabricated DBR shows a deviation of 0.2 nm of the stop-band central-wavelength compared to the targeted one. This approach holds significant interest for the III-V semiconductor community and epitaxial growth techniques. Measurement and realized without preliminary accurate cell flux calibrations. This method relies on the measurements of the optical indices' dispersion over wide spectral range (400 – 1400 nm) at growth temperature (600°C) of AlGaAs alloys. To do so, in-situ reflectance measurement is used combined with ex-situ layer thickness and composition measurement by X-ray diffraction. The DBR sample is characterized by X-ray diffraction and Fourier transform infrared reflectance, resulting in a deviation of 0.2 nm of the stop-band central-wavelength compared to the targeted one.