Inhomogeneous broadening of intersubband transitions in ${\mathrm{In}}_{0.45}$${\mathrm{Ga}}_{0.55}$As/${\mathrm{Al}}_{0.45}$${\mathrm{Ga}}_{0.55}$As multiple quantum wells

The contributions of homogeneous and inhomogeneous broadening mechanisms to the linewidth of an intersubband transition in an ${\mathrm{In}}_{0.45}$ ${\mathrm{Ga}}_{0.55}$As/${\mathrm{Al}}_{0.45}$ ${\mathrm{Ga}}_{0.55}$As multiple quantum well are determined by line-shape fitting and saturation intensity spectroscopy. An intersubband transition at 327 meV is found with a total linewidth of 36 meV and an underlying homogeneous linewidth of 14 meV. The sizes of various sources of inhomogeneous broadening are estimated and the implications for intersubband nonlinear optics are discussed.