Time resolved ultrafast dynamic excitations in semiconductors

Roger, Thomas (2013). Time resolved ultrafast dynamic excitations in semiconductors. University of Birmingham. Ph.D.

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Abstract

A time-resolved ellipsometry technique has been developed using a home- built and calibrated ellipsometer. The design and optimisation of the ellip- someter has been chosen carefully to study low absorption materials. The ellipsometric angles (Ψ and ∆) are measured in good agreement with commercial ellipsometry equipment. An optical model is constructed to find accurately the thin film thickness’ and dielectric function dispersions of the complex multi-layer samples. The values are then fit as a function of time allowing measurement of the transient change in dielectric function. The changes of complex dielectric function are modelled using a Drude approximation revealing interesting behaviour of the scattering processes and carrier concentration in samples of nc-Si:H and silicon nitride (SiN\(_x\)). In samples of nc-Si:H we find that the carriers adopt a classical distribution through analysis of the Fermi integrals and that recombination processes conserve the average temperature of electrons, suggesting that there is no preference for recombination of carriers with higher energies. This is contrary to current understanding of carrier dynamics in bulk semiconductors.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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