IR photothermal and spectroscopic analysis of proton-irradiated 4H-SiC

The effect of the proton irradiation dose on thermal transport anisotropy, free carrier density, and defect formation in 4H-SiC is studied by thermal wave scattering and infrared spectroscopy. Thermal waves are generated by infrared laser pulses, and the in-plane and cross-plane thermal diffusion length are measured using the deflection of a laser probe beam due to the mirage effect. The effect of proton irradiation dose on in-plane and cross-plane thermal diffusivity is measured as a function of depth. Proton irradiation is shown to cause significant damage primarily in the direction perpendicular to the sample surface. Irradiation-induced free carriers contributing to heat transport in the sample plane are revealed by Kramers-Kronig analysis of the infrared reflectivity spectra of the studied samples. Measurements of thermal diffusion lengths in the irradiated samples are converted to depth profiles of defect density. It is shown that the highly damaged zone in irradiated 4H-SiC thickens and approaches the proton reaching depth with increasing the irradiation dose. Thermal wave scattering complemented by infrared spectroscopy is proposed as an effective approach for the directional analysis of irradiation-induced changes in physical and structural properties of materials.