The development of the simulation methodology for steady-state thermoreflectance technique

The growing interest in the low-dimensional structures research has necessitated the development of non-contact optical methods for their thermal properties measurement. Thermoreflectance method allows thermal conductivity evaluation based on the analysis of material reflection coefficient change due to the laser radiation absorption and subsequent heating of the sample. Transient thermoreflectance in the frequency-domain (FDTR) and in the time-domain (TDTR) are already widely used for such measurements. More recent steady-state thermoreflectance method (SSTR) has the advantage above TDTR and FDTR which lies in the possibility to perform direct measurements resulting in higher accuracy and ease of measurement procedure. The current work is dedicated to the development of the approach for SSTR technique simulation. It includes the description of experimental procedure and the data collection, analytical and numerical data processing, finite elements simulation and the verification of the results. The proposed methodology has been performed on the example of 3 samples: Ge, Si, GaAs. The experiment included the measurement of the radiation power absorbed and reflected by the samples. Then, analytical and numerical models have been derived and used to calculate absorption and reflection coefficients taking in account Fabry-Perot effect. The finite elements model has been carried out to simulate electromagnetic heating of the studied samples and to evaluate their temperature. The model took into the consideration a normal distribution of a laser beam its diameter. For the model validation the temperature maps captured by a thermal imager have been compared with the numerically simulated ones. The discrepancy did not exceed 9%. The performed approach can be used for SSTR setup calibration and analysis of thermal processes in the samples under study.