Free carrier-induced optical nonlinearities in β-Ga2O3 single crystals at 355 nm

Abstract

Gallium oxide (Ga2O3) is a promising candidate in future photonic integrated circuits devices due to its ultra-wide band gap and high stability. However, the nonlinear optical properties of Ga2O3 still remain elusive. In this work, we investigate the free-carrier absorption and refraction in pristine β-Ga2O3 single crystal via the degenerate pump-probe measurement with phase object technique at 355 nm wavelength. The free-carrier absorption cross-section and free-carrier refraction index of β-Ga2O3 on the sub-nanosecond time scale are determined to be ∼0.6 × 10−22 m2, and ∼−0.62 × 10−28 m3, respectively. And the two-photon absorption coefficient of β-Ga2O3 is characterized as ∼0.53 × 10−11 m W−1. It is found that the free-carrier absorption and free-carrier refraction effect in β-Ga2O3 are significantly smaller than that in other wide bandgap semiconductors such as GaN and ZnO. Our results can serve as guidelines for designing β-Ga2O3 based ultra-low loss waveguides and integrated photonic applications in UV spectral range.