Abstract
The expression of the time evolution of the distribution function of hot electrons photoexcited by a laser pulse in the conduction band of a semiconductor under extreme quantum limit conditions is calculated. The transformation, justified in previous papers, of the master equation into a Fokker-Planck equation is used. The notions of diffusion and of drift velocity in the electron energy space are rigorously introduced. Finally, the time evolution of the mean electron energy is calculated and the influence of different scattering mechanisms and of various physical parameters is discussed.