Abstract
The dynamics of the phase transition from an electron-hole plasma to an exciton gas is studied during pulsed excitation of heterostructures with Si1 − x Ge x /Si quantum wells. The scenario of the phase transition is shown to depend radically on the germanium content in the Si1 − x Ge x layer. The electron-hole system decomposes into a rarefied exciton and a dense plasma phases for quantum wells with a germanium content x = 3.5% in the time range 100–500 ns after an excitation pulse. In this case, the electron-hole plasma existing in quantum wells has all signs of an electron-hole liquid. A qualitatively different picture of the phase transition is observed for quantum wells with x = 9.5%, where no separation into phases with different electronic spectra is detected. The carrier recombination in the electron-hole plasma leads a gradual weakening of screening and the appearance of exciton states. For a germanium content of 5–7%, the scenario of the phase transition is complex: 20–250 ns after an excitation pulse, the properties of the electron-hole system are described in terms of a homogeneous electron-hole plasma, whereas its separation into an electron-hole liquid and an exciton gas is detected after 350 ns. It is shown that, for the electron-hole liquid to exist in quantum wells with x = 5–7% Ge, the exciton gas should have a substantially higher density than in quantum wells with x = 3.5% Ge. This finding agrees with a decrease in the depth of the local minimum of the electron-hole plasma energy with increasing germanium concentration in the SiGe layer. An increase in the density of the exciton gas coexisting with the electron-hole liquid is shown to enhance the role of multiparticle states, which are likely to be represented by trions T + and biexcitons, in the exciton gas.
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Original Russian Text © V.S. Bagaev, V.S. Krivobok, S.N. Nikolaev, E.E. Onishchenko, A.A. Pruchkina, D.F. Aminev, M.L. Skorikov, D.N. Lobanov, A.V. Novikov, 2013, published in Zhurnal Eksperimental’noi i Teoreticheskoi Fiziki, 2013, Vol. 144, No. 5, pp. 1045–1060.
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Bagaev, V.S., Krivobok, V.S., Nikolaev, S.N. et al. Dynamics of the phase transitions in the system of nonequilibrium charge carriers in quantum-dimensional Si1 − x Ge x /Si structures. J. Exp. Theor. Phys. 117, 912–925 (2013). https://doi.org/10.1134/S1063776113130074
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DOI: https://doi.org/10.1134/S1063776113130074