Simultaneously Mapping of In-Depth Thermal Diffusivity and Effective Infrared Absorption Coefficient of Silicon-Doped Gallium Arsenide Wafer Using Lock-in Thermography

In this work, we report on simultaneously mapping of the thermal diffusivity and effective infrared absorption coefficient of GaAs wafer using infrared lock-in thermography. The phase images were extracted from the temperature modulation of the investigated surface at different excitation frequencies, by applying the lock-in detection for each pixel of the recorded image. The resulting images were analyzed using the thermal wave model in the transmission configuration. The thermal diffusivity and the effective infrared absorption coefficient were estimated from the best fit of the theoretical model to the experimental data applied for each pixels of the phase images. Finally, we used different image filters to decrease the estimation errors of the parameters and to enhance the quality of the images. The results demonstrate that the lock-in thermography technique in transmission configuration provides spatial information for both (effective) infrared absorption coefficient and thermal diffusivity of semiconductor crystals. Moreover, the possibility of using lock-in thermography and photothermal radiometry microscopy in investigation of large area and thin films is discussed.