Abstract
Microcrystalline SiGe was obtained by using laser-induced crystallizing a-SiGe films deposited by plasma-enhanced chemical vapour deposition. The dynamics of dense electron–hole plasma in SiGe films, subsequent to photoexcitation by a 150 fs optical pulse, is studied by measuring time-resolved changes in the reflectivity of the films. The initial electron–hole pair densities are between 2.2 × 1019 and 2.6 × 1020 cm−3. Typical traces of the time-resolved reflectivity change are initiated with a rapid decrease, followed by a slower recovery of the reflectivity change, which can be well simulated by a double exponential curve. The fast component of relaxation time τf varies in the range of 0.75–0.79 ps and is almost independent of the initial carrier density. The slower component of relaxation time τs increases with the increase of the initial carrier density and varies in the range of 6.97–17.70 ps. The fast component τf could result from carrier cooling and the cooling rate may be due to carrier–phonon deformation potential scattering at the high excitation density. The recombination and trapping of the thermalized carriers are considered to be the possible origin for the slow component τs of the relaxation time of reflectivity recovery dynamics.
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