Growth-rate-dependent ultrafast carrier dynamics and electro-optic response in GaAs epitaxial films on misoriented substrates

The influence of growth temperature and growth rate on the ultrafast carrier dynamics and electro-optic response of GaAs films grown on GaAs(100) substrates misoriented by 10° toward [111]A was investigated using time-resolved reflectance (TRR), atomic force microscopy (AFM), and photoreflectance (PR) spectroscopy. AFM revealed step-bunching at low growth rates (Vg = 0.2 μm/h) and smoother step-flow morphology at higher rates (Vg = 0.8 μm/h). Biexponential TRR analysis identified a slow relaxation time component (τ2 = 2.4 −48.6 ps) that separates the two growth-rate series. Contrary to the expected behavior for a spatially uniform defect distribution, the rougher, step-bunched samples exhibit longer relaxation times than the smoother samples, consistent with a diffusion-limited regime requiring carrier migration toward spatially localized defect centers before recombination. The PR spectra exhibited Franz–Keldysh oscillations yielding fields between 226 and 262 kV/cm, consistent with the depletion field at the heavily Si-doped substrate/epilayer interface, without requiring additional mechanisms; a piezoelectric contribution from the [111]A misorientation is expected to be secondary. No significant correlation was found between the relaxation time and the internal field, indicating distinct mechanisms operating at different depths. These results provide a mechanistic framework distinguishing structural from doping-related effects on carrier relaxation and the electro-optic response of GaAs epilayers grown on highly misoriented substrates.