光ヘテロダイン光熱変位測定による半導体の熱物性評価(1) 理論解析モデルの構築

The heat generated by the electronic device operation causes a decreasing its performance. Therefore, it is necessary to evaluate the heat generation and its propagation in semiconductors. We build a laser eterodyne photothermal displacement (LH-PD) system to evaluate thermal properties of semiconductors. When an xcitation laser is irradiated on the semiconductor surface, the surface is thermally expanded under the influence of heat generated by nonradiative recombination of the photoexcited carriers. The LH-PD method can directly detect a surface displacement and its time variation by non-contact and non-destructive. Moreover, there is a possibility to evaluate thermal properties such as thermal conductivity (κ) by reproducing the time variation of a surface displacement with theoretical calculations. We carried out LH-PD measurements and theoretical calculations based on a thermal diffusion equation with the photoexcited carrier diffusion to verify their validity using Si and GaAs substrate which are already known physical properties. As a result, the calculated results agreed well with the experiments. Therefore, we found that heat conduction and carrier diffusion affect the time variation of the surface displacement. Consequently, it was clearly shown that the LH-PD method was useful for evaluating thermal properties of semiconductors.