Experimental aspects of hot electron distribution functions

A review is presented on the experimental efforts to obtain hot electron distribution functions in bulk materials in high d.c. electric fields. Three optical methods will be discussed in detail: (i) inter- and intraband absorption measurements, (ii) emission due to radiative transitions between band states, and band- and impurity states, (iii) inelastic light scattering experiments. A distinction is made between methods which yield the energy distribution functions and those which give information on the anisotropic distribution of hot carriers in the momentum space. The latter experiments involve a determination of the electric field induced dichroism in absorption or emission and the dependence of the scattering cross section on scattering geometry in inelastic light scattering experiments. The influence of the nonequilibrium phonon distribution on the interpretation of the experimental results is discussed, too. In addition, current work on energy distribution functions of hot carriers in quantizing magnetic fields as obtained from absorption or emission of infrared radiation due to transitions of carriers between Landau states or magnetic field split impurity states will be presented.