In Situ Controlled Growth of Low-Temperature GaAs and Its Application for Mode-Locking Devices

We report on the potential of reflectance difference spectroscopy (RDS) in realizing high reproducibility, optimization of growth conditions, and in situ control for growth of extremely thick high quality GaAs layers at low substrate temperatures (LT). The amplitude of the observed anisotropy in the RDS caused by the linear electro-optic effect is directly related to the incorporated As antisite density. Therefore, in situ RDS allows a real time determination of nonstoichiometry and hence, of the electrical and optical properties of the layers. We show that extremely thick LT-GaAs layers (up to 14 µm) grown by molecular beam epitaxy (MBE) with optimized growth parameters can be successfully implemented as a material for obtaining self-starting mode-locking of a Nd:glass fiber laser.