Large third-order nonlinearity of nonpolar A-plane GaN film at 800 nm determined by Z-scan technology

Abstract

We report an investigation on the optical third-order nonlinear property of the nonpolar A-plane GaN film. The film sample with a thickness of ~2 μm was grown on an r-plane sapphire substrate by metal-organic chemical vapor deposition system. By performing the Z-scan method combined with a mode-locked femtosecond Ti:sapphire laser (800 nm, 50 fs), the optical nonlinearity of the nonpolar A-plane GaN film was measured with the electric vector E of the laser beam being polarized parallel (//) and perpendicular (⊥) to the c axis of the film. The results show that both the third-order nonlinear absorption coefficient β and the nonlinear refractive index n₂ of the sample film possess negative and large values, i.e. β_//= −135 ± 29 cm/GW, n_2//= −(4.0 ± 0.3) × 10⁻³ cm²/GW and β_⊥ = −234 ± 29 cm/GW, n_2⊥= −(4.9 ± 0.4) × 10⁻³ cm²/GW, which are much larger than those of conventional C-plane GaN film, GaN bulk, and even the other oxide semiconductors.

Keywords:

• nonpolar A-plane GaN
• third-order nonlinearity
• Z-scan technique
• thin film

Acknowledgement

The authors would like to acknowledge Dr. Kai Wang (Wuhan National Laboratory for Optoelectronics) for his kindly technical support and helpful discussion.

Funding

This work was supported by the Young Scientists Fund of the National Natural Science Foundation of China under the [grant number11104365] and the Open Fund of Hubei Key Laboratory of Low Dimensional Optoelectronic Material and Devices under the [grant number 13XKL02002].