Simulation of lead selenide film heating by CW laser radiation taking into considering oxidation process

The heating characteristics of a lead selenide (PbSe) film under continuous laser radiation were investigated, accounting for the nucleation and increase in the thickness of an oxide phase layer. It is shown that oxidation of the PbSe film reduces the heating rate and lowers the maximum temperature due to a decrease in the fraction of absorbed laser radiation within the oxide phase. The modeling results presented in this work substantiate earlier experimental findings. For the first time, the explanation of the laser heating mechanism of the PbSe film enabled determining the most effective laser exposure duration to form structures with specified optical characteristics. The study was conducted using analytical modeling. A particular solution of the heat conduction equation was employed to describe the heat source. The optical properties of the film were characterized using Fresnel equations for light reflection and transmission. Based on previously obtained experimental data, an analytical model was developed to describe the heat source in the film, considering changes in its optical properties due to the formation of a lead selenide oxide layer and its increasing thickness. The findings show that, when the PbSe film is exposed to continuous laser radiation with a wavelength of 405 nm, the extinction coefficient of the film, kf, decreases from 0.488 to 1.62∙10–3 due to the formation of an oxide layer. In this case, the refractive index of the film, nf, similarly decreases from 3.532 to 1.925. The film absorption coefficient at the laser wavelength decreases from 0.68 to 0.03 during irradiation. As the thickness of the oxide phase increases from 0 to 600 nm, the temperature growth in the irradiated zone slows down, and the maximum temperature shifts from the surface toward the film-substrate interface. When exposed to continuous laser radiation with a power density of about 340 W/cm² for 9 s, the maximum film temperature does not exceed 275 °C. The obtained results can be applied in the development of mid-infrared spectrum photo detectors based on PbSe film. Laser annealing of the film allows local and controlled changes in the optical and electrical properties of the PbSe film within a narrow range of values, thereby influencing the photo sensitivity of the film used as a detector for midand far-infrared radiation.

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