Nanosecond light-induced transient absorption in As2S3: Self-trapped exciton recombination in amorphous chalcogenides

• Excitation wavelength dependent spectral and temporal behaviors of ns TA
• TA is found to be largest at low temperatures.
• Relaxation kinetics of TA gets faster at higher temperatures.
• Photoexcited carriers have longer life time in deep rather than shallow traps.
• TA grows up quadratically with excitation fluence-two photon process.

In this article, we report spectral and temporal dependence of nanosecond (ns) transient absorption (TA) in a-As2S3 thin film when illuminated with the above (355 nm) and near (532 nm) bandgap laser. Detailed temperature dependent study of TA by 355 nm excitation demonstrates the decrease in TA together with faster relaxation kinetics at higher temperatures. Such observation of the change in kinetics and magnitude of TA with temperature is well consistent with the self-trapped exciton recombination mechanism. In addition to this, our experimental results also reveal that the long wavelength component of TA decays faster than the short wavelengths which provides interesting insights that the trapped exciton possesses longer lifetime in deep traps than in shallow traps. The excitation fluence dependent study further reveals that TA exhibits a quadratic dependence on laser dose which yields that the effects are originating from the two-photon process.