What is the cut-off wavelength of GaAs photodiodes ?

The long end of the spectral response of GaAs photodiodes is limited by the bandgap energy of GaAs which is 1.42eV (corresponding to about 870nm). Hence incoming light with a wavelength beyond that limit (i.e. light with a larger wavelength) will not be absorbed as GaAs is transparent for such wavelengths. In the wavelength region from  830nm to 860nm Albis’ GaAs photodiodes have an excellent quantum efficiency close to one and hence a responsivity  up to 0.6 A/W. Below 830nm the quantum efficiency decreases gradually due to recombination losses at the semiconductor surface.