Dynamics of Photoinduced Charge Carrier and Photothermal Effect in Pulse-Illuminated Narrow Gap and Moderate Doped Semiconductors

When a sample of semiconducting material is illuminated by monochromatic light which photon energy is higher than the energy gap of the semiconductor, the part of absorbed electromagnetic energy is spent on the generation of pairs of excess carriers that are bound by Coulomb attraction. Photo-generated pairs diffuse through the material as a whole according to the density gradients established carrying the part of excitation energy through the semiconducting sample. This energy is indirectly transformed into heat where the excess negatively charged electron recombines with a positively charged hole and causes additional local heating of the lattice. In this paper, based on ambipolar diffusion partal differential equation in approximation of low-level injection, the spectral function of photoinduced charge carrier distribution was calculated and models of spectral functions of surface recombination heat sources were derived. By applying the inverse Laplace transform to derived models, the dynamics of recombination photoinduced heat sources at surfaces of semiconducting samples was studied for pulse optical excitations of very short and very long duration. It was shown that the photoexcited charge carriers could significantly affect semiconductor heating in dependence on pulse duration and velocity of surface recombinations, consequently influencing the performance of nanoelectronic and optoelectronic semiconductor devices.