Optical absorption in a waveguide based on an n-type AlGaAs heterostructure

Free carrier absorption of optical radiation in layers of an AlGaAs/GaAs heterostructure is studied by the method of probe radiation coupling in order to determine the absorption cross section parameter in the AlGaAs material with a high (22%) aluminium concentration. For this purpose, we have fabricated special samples based on AlGaAs/GaAs heterostructures simulating an n-type-doped laser waveguide with carrier concentrations in the range 5 × 10¹⁶ – 3 × 10¹⁷ cm^-3. The doping profile and the composition and thickness of layers are measured and the temperature and spectral dependences of the absorption coefficient are studied. It is shown that an increase in temperature and in the probe wavelength leads to an increase in the absorption in the heterostructure layers.