Time-resolved, nonequilibrium carrier dynamics in Si-on-glass thin films for photovoltaic cells

Abstract

A femtosecond pump-probe spectroscopy method was used to characterize the growth process and transport properties of amorphous silicon-on-glass, thin films, intended as absorbers for photovoltaic cells. We collected normalized transmissivity change (ΔT/T) waveforms and interpreted them using a comprehensive three-rate equation electron trapping and recombination model. Optically excited ∼300-500 nm thick Si films exhibited a bi-exponential carrier relaxation with the characteristic times varying from picoseconds to nanoseconds depending on the film growth process. From our comprehensive trapping model, we could determine that for doped and intrinsic films with very low hydrogen dilution the dominant relaxation mode was carrier trapping; while for intrinsic films with large hydrogen content and some texture, it was the standard electron-phonon cooling. In both cases, the initial nonequilibrium relaxation was followed by Shockley-Read-Hall recombination. An excellent fit between the model and the ΔT/T experimental transients was obtained and a correlation between the Si film growth process, its hydrogen content, and the associated trap concentration was demonstrated.

Time-resolved, nonequilibrium carrier and coherent acoustic phonon dynamics in (Cd, Mg)Te single crystals for radiation detectors

“…Despite the perfect fit shown in figure 3, the physics insight in such a phenomenological approach is quite limited, so for a much more in-depth understanding of the carrier photoexcitation and, first of all, the role of traps (band-tail states) in subsequent relaxation dynamics in our CMgT crystals, we have adopted a model presented in [30]. The model has been developed for nano-Si films, known to have extended concentration of trap states, and unifies the approaches presented in [31,32] for time-resolved carrier dynamics in amorphous Si films and in low-temperaturegrown GaAs crystals, respectively.…”

“…1 as an example), we fitted our experimental probe-normalized, transient-reflectivity DR/R waveforms, measured in both one-and two-color setups, to the trapping and relaxation model that we developed and presented in Ref. 9. We note that in Fig.…”

Photoconductive and electro-optic effects in (Cd,Mg)Te single crystals measured in an experiment-on-chip configuration

“…Time-resolved measurements of the CMgT photoresponse were performed using the laser system described in detail in [21]. Briefly, we used a mode-locked Ti:sapphire laser emitting a train of ~100-fs pulses at 820-nm wavelength and a 76-MHz repetition rate.…”