Real-time in-situ flux monitoring by wavelength-modulated atomic absorption spectroscopy in molecular beam epitaxy: Application to Ga flux measurement

A flux monitoring set-up is described, based on wavelength-modulated atomic absorption spectroscopy (WMAAS) in-situ real-time measurements. It is particularly suited for element III fluxes monitoring during the growth of III-V semiconductors and heterostructures inside a molecular beam epitaxy (MBE) chamber. The tunable source is a blue-violet laser diode mounted in an external cavity, followed by an interferometer required to actively stabilize the emitted wavelength. Measurements have been carried out for the Ga element at 403.3 nm, with a growth rate in the range 0.027-1.5 ML/s on GaAs. The WMAAS signal shows a linear dependence on the growth rate over the whole range studied here. The uncertainty and low flux limit are measured to be 0.01 ML/s at most.