Abstract
We report the different nonlinear optical mechanisms and defect-related carrier dynamics in Sn-doped β-Ga2O3 crystal by utilizing time-resolved pump-probe technique based on phase object under UV excitation. The obtained nonlinear optical parameters arise from bound electron can be well explained by the theoretical calculation of two-band model and Kramers-Kronig transformation. By tuning the probe wavelength, the carrier nonlinearity can be modulated greatly due to additional absorption of defects within the bandgap. The results reveal that by choosing a proper probe wavelength that matches the defect state to the valence band, the nonlinear absorption and refraction of the carriers can be greatly enhanced, which provides an important reference for the design of gallium oxide-based waveguide materials and all-optical switching materials in the future.
Highlights
Beta-phase gallium oxide (β-Ga2O3) is a transparent conductive oxide with an ultra-wide band gap of 4.9 eV (Tippins, 1965)
The nonlinear effects caused by bound electrons are instantaneous, while the recovery time of the nonlinear effects caused by carriers is relatively long
We found that the theory is applicable to gallium oxide, and the refraction sign changed at different probe wavelengths
Summary
Beta-phase gallium oxide (β-Ga2O3) is a transparent conductive oxide with an ultra-wide band gap of 4.9 eV (Tippins, 1965). Okan Koksal et al presented optical pump-probe spectroscopy results on defect-assisted recombination of photoexcited carriers in β-Ga2O3 (Koksal et al, 2018). They used a single wavelength to probe the additional carrier absorption of polarization-related defect states, but ignored the carrier refraction. We studied the variation process of the nonlinear absorption/refraction of Sn-doped β-Ga2O3 with delay time by phase object pump-probe technique (POPP) at different probe wavelengths. The pump light and probe light focus on the same point of the sample at a small angle (less than 5°), and the nonlinear dynamic process is explored by adjusting the delay time of the two beams.
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