氮化銦薄膜之非線性光學特性

Abstract

Indium nitride (InN) with a narrow direct band gap has superior electronic transport properties to other group-III nitrides so that InN has become attractive for various applications such as high-frequency electronic devices, near-infrared optoelectronics, and high-efficiency solar cells. Because of its narrow band gap, InN can be easily integrated with an optical fiber laser to achieve compact optical system. Recent dramatic increase of information transportation through internet requires switches operating at high rate for future systems development. All-optical switches based on the nonlinear optics may provide solution for faster switches. The bandwidth of optical switch would reach beyond 1 THz unattainable by any electronic switch. In general, all-optical switching technology requires a nonlinear material with large nonlinear refraction and small linear absorption. The InN film photoexcited at wavelength of 1550 nm shows the large optical bleaching and its recovery time would be less than a few picoseconds, which makes InN an excellent candidate to realize all-optical switch in the telecommunication regime. Despite these advantageous prospects, studies on nonlinear phenomena of InN are relatively limited and most experiments have been carried out at selected wavelengths, such as =800 nm or 1550 nm, and spectroscopic study is few. This is mainly due to the lack of a femtosecond laser source and the corresponding detection system in the near-infrared (NIR) spectral range. Here, we report the third-order nonlinearities of InN films grown on a sapphire substrate characterized using the Z-scan technique with femtosecond pulses in the wavelength range from 800 to 1600 nm. The nonlinear absorption cross-section is calculated from the open aperture (OA) Z-scan signals, whereas the nonlinear refraction coefficients are obtained from the close aperture (CA) signals. InN film with band gap energy (Eg) of ~0.65 eV exhibits strong saturable absorption in the entire spectral range. For another InN film whose PL peak energy shift to ~0.76 eV, a transition of NLA mechanism from SA to reverse SA is observed at the wavelength of ~1500 nm. The close aperture Z-scan signals show the valley-peak behavior in the whole spectral range, indicating self-focusing due to the third-order nonlinear refraction.

Indium nitride (InN) with a narrow direct band gap has superior electronic transport properties to other group-III nitrides so that InN has become attractive for various applications such as high-frequency electronic devices, near-infrared optoelectronics, and high-efficiency solar cells. Because of its narrow band gap, InN can be easily integrated with an optical fiber laser to achieve compact optical system. Recent dramatic increase of information transportation through internet requires switches operating at high rate for future systems development. All-optical switches based on the nonlinear optics may provide solution for faster switches. The bandwidth of optical switch would reach beyond 1 THz unattainable by any electronic switch. In general, all-optical switching technology requires a nonlinear material with large nonlinear refraction and small linear absorption. The InN film photoexcited at wavelength of 1550 nm shows the large optical bleaching and its recovery time would be less than a few picoseconds, which makes InN an excellent candidate to realize all-optical switch in the telecommunication regime. Despite these advantageous prospects, studies on nonlinear phenomena of InN are relatively limited and most experiments have been carried out at selected wavelengths, such as =800 nm or 1550 nm, and spectroscopic study is few. This is mainly due to the lack of a femtosecond laser source and the corresponding detection system in the near-infrared (NIR) spectral range. Here, we report the third-order nonlinearities of InN films grown on a sapphire substrate characterized using the Z-scan technique with femtosecond pulses in the wavelength range from 800 to 1600 nm. The nonlinear absorption cross-section is calculated from the open aperture (OA) Z-scan signals, whereas the nonlinear refraction coefficients are obtained from the close aperture (CA) signals. InN film with band gap energy (Eg) of ~0.65 eV exhibits strong saturable absorption in the entire spectral range. For another InN film whose PL peak energy shift to ~0.76 eV, a transition of NLA mechanism from SA to reverse SA is observed at the wavelength of ~1500 nm. The close aperture Z-scan signals show the valley-peak behavior in the whole spectral range, indicating self-focusing due to the third-order nonlinear refraction.