Modulating the nonlinear absorption response of SnO_x thin films via phase engineering

Area of Science:

• Materials Science
• Optoelectronics
• Thin Film Technology

Background:

• The electronic and optical properties of amorphous oxide semiconductors are critically dependent on their phase composition.
• Understanding and controlling nonlinear optical (NLO) responses in transparent conductive oxides is crucial for advanced optical applications.

Purpose of the Study:

• To investigate the modulation of ultrafast nonlinear optical (NLO) response in SnO2 and SnO thin films.
• To explore the effect of tuning oxygen partial pressure during film sputtering on the NLO properties.

Main Methods:

• Fabrication of SnO2 and SnO thin films via sputtering with controlled oxygen partial pressure.
• Femtosecond and picosecond Z-scan techniques to measure two-photon absorption (TPA) and nonlinear absorption coefficients (βeff).
• Femtosecond degenerate pump-probe spectroscopy to analyze carrier dynamics and absorption mechanisms.

Main Results:

• Intermediate phases in SnO2 and SnO films did not significantly impact the two-photon absorption (TPA) response.
• The effective nonlinear absorption coefficient (βeff) was enhanced in intermediate SnO2-x and SnOx phases due to altered Sn2+/Sn4+ ratios.
• Femtosecond pump-probe results revealed accelerated carrier trapping in SnOx (SnO-rich) and suppressed TPA in SnO2-x (SnO2-rich) films, with carrier-induced absorption dominating the latter.

Conclusions:

• Oxygen partial pressure is an effective parameter for tuning the nonlinear optical response of SnO2 and SnO thin films.
• The interplay between phase composition, carrier dynamics, and defect states dictates the NLO behavior in these materials.
• This study provides a simple method to modulate the NLO properties of transparent conductive oxides for potential device applications.