Effect of excitation level on the optical properties of GaAs/AlGaO microdisks with an active region containing InAs quantum dots

The effect of the excitation level on the intensity and width of whispering-gallery-mode (WGM) lines in microdisks with an asymmetric air/GaAs/AlGaO waveguide and an active region containing InAs quantum dots is studied using microphotoluminescence spectroscopy. At high pump levels, overheating of the active region takes place, which leads to a long-wavelength shift of the gain spectrum; in addition, the shape of the spectrum changes due to the saturation of the ground and excited states and to many-particle interactions. As a consequence, the behavior of intensities and linewidths of WGMs as functions of the optical-pump power density is determined by the spectral positions of the modes with respect to the gain peaks and may differ considerably for different modes. The long-wavelength shift of WGM lines caused by active-region overheating is partially compensated by a short-wavelength shift, which occurs due to the dependence of the effective refractive index of the waveguide on the concentration of free charge carriers.