Different Non Destructive Photothermal Deflection Techniques to Determine Thermal Properties of Bulk Semiconductors

In this paper we will describe and compare different non destructive Photothermal Deflection methods easy to develop and not expensive which permit the determination of the thermal diffusivity of bulk semiconductor material. The first method consists to draw the experimental amplitude and phase of the photothermal deflection signal versus square root modulation frequency. The sample placed in air is heated thanks to a modulated pump uniform beam. The only difference between the first and the second method is that in the second method the sample is covered by a thin graphite layer. We show in this study that the first method is only sensitive to the thermal diffusivity of the sample however the second method is sensitive for both thermal diffusivity and thermal conductivity. Finally the third method which is a spectroscopic one consists to draw the experimental phase and amplitude of the photothermal signal versus wavelength at a fixed modulation frequency. The sample is immersed in a CCl4 filled cell. In this study we show that the phase signal saturate for high and low optical absorption coefficient values. The phase difference between the two saturated regions is function of the thermal diffusivity of the sample.