Wide bandgap semiconductors are widely used in photonic technologies due to their important features, such as large optical windows, fewer energy losses, and fast operational capacity. Next-generation devices require extensive investigation to achieve the desired stability and scalability. Silicon carbide (SiC) is a wide bandgap semiconductor with high optical nonlinearities, large electron transport, and a high breakdown threshold. Integration of SiC in nonlinear photonics requires a systematic analysis of the multiphoton contribution to the device functionality. Here, multiphoton absorption in SiC photodetector is investigated using phase-modulated femtosecond pulses. Quantification of multiphoton absorption is achieved by using a 1030nm phase-modulated pulsed laser. Our measurements show that although the bandgap is less than the energy of three photons combined, four-photon absorption (4PA) contributes to the photocurrent. We interpret 4PA as a phonon-assisted indirect transition from the valance band Γ point to the L point in the conduction band. Moreover, it is found that SiC withstands high excitation intensities, which is suitable for high-power applications.
Recently saturation effects in nonlinear processes have attracted attention of scientific community for both fundamental research and application. However, accurate determination of the emergence of saturation is still challenging, especially when multiple orders of absorption get involved. Here we present a simple method to characterize saturation absorption using phase-modulated femtosecond lasers. Second harmonic generation and photocurrents are measured for GaP photodetector. For high incident intensity, higher order modulation signals emerge and exhibit much stronger intensity dependence. We found that the higher order modulation signal could serve as a sensitive probe for saturation absorption. The investigation could be useful in fabricating ultrafast switches and multiphoton microscopy.
Defect distribution and their contribution to photocurrent is imaged in commercially available GaP, GaAsP and GaN using phase modulated multi-photon microspectroscopy. Results show that contributions from defects dominate the photocurrent from GaAsP and GaN. In GaP, such contributions are substantially less. Fabrication process of GaAsP and GaN could be optimized to improve their functionality as photodiodes. The method we have implemented can be used as an ‘in-operando’ characterization tool for understanding the underlying processes that contribute to the external signals in semiconductor devices.
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