Time-resolved infrared radiometry of laser-heated silicon

Time-resolved pulsed photothermal radiometry techniques for the study of the thermal and optical properties of silicon are discussed. By the use of a one-dimensional thermal diffusion equation, a theoretical description for the transient thermal radiation can be developed. Results obtained for relatively heavily doped samples (~0.002 Ω-cm) show that the pulsed photothermal radiometry is an excellent remote diagnostic technique for silicon over a wide range of relatively heavy doping levels. For lightly doped samples (~5 Ω-cm), an anomalously large thermal radiation signal is observed that contradicts the predictions of the thermal diffusion model. The phenomenon can be explained by the enhancement of the gray-body emissivity due to laser-generated free carriers. A simple theoretical model for the free-carrier effect is presented.