Electron and phonon temperature relaxation in semiconductors excited by thermal pulse

Electron and phonon transient temperatures are analyzed in the case of nondegenerate semiconductors. An analytical solution is obtained for rectangular laser pulse absorption. It is shown that thermal diffusion is the main energy relaxation mechanism in the phonon subsystem. The mechanism depends on the correlation between the sample length l and the electron cooling length lε in an electron subsystem. Energy relaxation occurs by means of the electron thermal diffusion in thin samples (l≪lε), and by means of the electron–phonon energy interaction in thick samples (l≫lε). Characteristic relaxation times are obtained for all the cases, and analysis of these times is made. Electron and phonon temperature distributions in short and long samples are qualitatively and quantitatively analyzed for different correlations between the laser pulse duration and characteristic times.