Nonequilibrium carrier dynamics in ultrathin Si-on-glass films

19th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures

Serafini, J.^1 ; Akbas, Y.^1 ; Crandall, L.^2 ; Bellman, R.^3 ; Williams, C Kosik^3 ; Sobolewski, Roman^1,2

Department of Physics and Astronomy, Laboratory for Laser Energetics, University of Rochester, Rochester

NY

14627-0231, United States^1

Department of Electrical and Computer Engineering, University of Rochester, Rochester

NY

14627-0231, United States^2

Corning Incorporated, Corning

NY

14831, United States^3

关键词: Electron-hole recombination;    Exponential relaxation;    Femtosecond pump probe spectroscopy;    Microcrystalline silicon films;    Nonequilibrium carrier dynamics;    Optical measurement;    Rate-equation models;    Trap concentration;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/647/1/012032/pdf
DOI  :  10.1088/1742-6596/647/1/012032

来源: IOP

【 摘 要 】

We present a femtosecond pump-probe spectroscopy approach for characterization of amorphous and microcrystalline silicon films grown on glass substrates. Such films are presently being considered as absorbers in tandem-type, Si-based photovoltaic cells. Our experiments consisted of time-resolved, two-colour femtosecond optical measurements, performed in the transmission mode in a wide range of delay times. Depending on the sample growth process, collected normalized transmissivity change (ΔT/T) waveforms exhibited a bi-exponential relaxation dynamics with the characteristic times varying from picoseconds to nanoseconds. Experimental data were interpreted using a three-rate-equation models, and the relaxation was identified as, depending on the Si film type, being dominated by either carrier trapping or electron-phonon cooling and followed by electron-hole recombination. An excellent fit between the model and the ΔT/T transients was obtained and a correlation between the Si film growth process, its hydrogen content, and the associated trap concentration was demonstrated.