【Substrate Papers】Sn doping into β-Ga₂O₃ by a KrF excimer laser

      Researchers from the Kyushu University have published a dissertation titled "Sn doping into β-Ga₂O₃ by a KrF excimer laser" in Applied Physics A.

Abstract

      We report on the first investigation of excimer laser doping of Sn species into β-Ga₂O₃ single crystalline substrates with a KrF excimer laser. A SnO₂ thin layer was formed on β-Ga₂O₃ substrate as a Sn source, and was irradiated with a deep ultraviolet (UV) pulsed laser beam to make Sn ions diffuse into the β-Ga₂O₃ substrate. Measurements of secondary ion mass spectrometry confirmed Sn diffusing into the β-Ga₂O₃ substrate and revealed Sn diffusion depth and profile variation with laser irradiation conditions, such as fluence, pulse number, and pulse repetition frequency. Although no Sn diffusion observed into the β-Ga₂O₃ after irradiation of the UV laser beam (10 shots with repetition rate of 1000 Hz) at fluence of 0.3 J/cm², Sn diffusion depth of 63 nm was confirmed in the sample irradiated at 0.5 J/cm². Taking into account of the absorption coefficient of β-Ga₂O₃ at the wavelength of KrF excimer laser light (248 nm), light intensity at about 70 nm from the surface was roughly estimated as approximately 60% of the incident one. It means that intensity at the 60 nm depth of the light irradiated at 0.5 J/cm² was nearly equal to that at the surface of the light at 0.3 J/cm², corresponding to the results of diffusion depths with irradiations at 0.5 and 0.3 J/cm². This correspondence might be explicable with temperature distribution from the surface, and the diffusion edge could be restricted by the depth at specific temperature. On the other hand, slight diffusion (about 5–10 nm in depth) of Sn was confirmed in the samples irradiated at a low fluence of 0.3 J/cm² when a shot number was as large as 10000–30000 at repetition frequency of 1000 Hz, and even at 0.2 J/cm² with 30000 shots when a repetition frequency was as high as 4000 Hz. These are probably due to extending the heating time by a substantial number of shots and an effect of heat accumulation caused by a short interval between laser pulses.

DOI：

https://doi.org/10.1007/s00339-025-08550-7