Time-resolved laser scanning photothermal microscopy for characterization of thermal properties of semi-insulating GaAs.

Abstract

The strong coupling effect of thermal and plasma waves disturbs the accurate characterization of thermal properties of semiconductors under super bandgap energy photon excitation. We propose a time-resolved laser scanning photothermal microscopy to decouple the thermo-electronic effect for accurate determination of the thermal diffusivity of a semi-insulating GaAs sample. The distinct advantage of the decoupling principle relies on that the scanning excitation of a laser beam on the sample surface introduces different transient and steady-state characteristics into the thermal and electronic parts of the photothermal response, where the transients between the thermal and electronic parts have a large time-scale separation, and the steady states show an enhanced thermal effect over the electronic effect. Therefore, the plasma wave is simply responsible for a negligible constant background in the thermo-electronic coupling. The theoretical and experimental results confirmed that the time-resolved photothermal signal is insensitive to the electronic transport parameters varying even by several orders of magnitude and can be used to determine the thermal diffusivity from its best fit. Moreover, the scanning excitation nature of this method allows for high-efficiency photothermal imaging of the sample to identify the thermal defects.