Effects of nonparabolicity on collective intersubband excitations

We have used inelastic light scattering to study the collective charge- and spin-density excitations associated with electronic intersubband transitions in GaSb-AlSb superlattices. The density of the photoexcited two-dimensional electron-hole plasma was controlled by varying the incident laser power. A comparison of experiment with detailed calculations of the response functions shows that the nonparabolicity of the conduction band must be properly included in order to yield quantitative agreement