Non-contact photothermal method for measuring thermal diffusivity and electronic defect properties of solids

A method of measuring thermal diffusivity of a solid, comprising the steps of:

• (a) providing a sample of the solid;
• (b) irradiating the solid with a periodic heat generating signal having a fixed period T.sub.0 and a pulse duration .tau..sub.p in a range from about zero to T.sub.0, wherein a photothermal signal is produced;
• (c) detecting said photothermal signal;
• (d) processing said photothermal signal using a signal processing means to measure a temporal fundamental Fourier component of the photothermal signal and to calculate a quadrature component of said fundamental Fourier component, and to correct said quadrature component for frequency dependent phase shifts due to said signal processing means to give an output quadrature value at said pulse duration .tau..sub.p ;
• (e) changing the pulse duration .tau..sub.p to a new value in said range and repeating steps (b) to (d) without further correcting for phase shifts;
• (f) repeating step (e) until said range has been scanned by the pulse duration .tau..sub.p ;
• and
• (g) fitting said output quadrature value to a theoretical model of the photothermal response of the repetitively irradiated solid to obtain the thermal diffusivity of the solid.

A method of measurement of thermal diffusivity in a semiconductor having a charge carrier system, comprising;

• (a) providing a sample of the semiconductor;
• (b) irradiating the semiconductor with a light pulse having a pulse duration .tau..sub.p and repetition period T.sub.0, wherein one of pulse duration .tau..sub.p and repetition period T.sub.0 but not both are scanned while the other is maintained at a preselected value, the light pulse having a wavelength suitable to produce photoexcited electronic carriers, wherein after the light pulse is switched off recombination of said photoexcited electronic carriers occurs to release energy thereby causing a temporary increase in infrared emissivity and the temperature of the semiconductor responsively producing a photothermal signal;
• (c) detecting said photothermal signal and inputting said photothermal signal into a signal detection means to measure a temporal fundamental Fourier component of said photothermal signal and to provide an output signal;
• and
• (d) fitting said output signal to a theoretical model of the photothermal response of the repetitively irradiated semiconductor sample to obtain the thermal diffusivity of the semiconductor.