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Institute of Optics


Wave Packets in a Semiconductor Superlattice: A Theoretical Study of Coherent Dynamics in a Solid State System


Mark L. Biermann

We present a theoretical study of the coherent dynamics of carriers in semiconductor superlattices that have been photo-excited by a short laser pulse. The theoretical formalism applied in this study is divided into two steps. First, the superlattice bandstructure and the envelope functions of the superlattice, zone-center eigenstates are calculated. This is accomplished using a k•p, empirical, local pseudopotential approach, which can be applied to both III-V and II-VI superlattice systems. The bandstructure formalism describes superlattices with a variety of growth orientations and accounts for the effects of lattice mismatch within the superlattice and applied stress or DC electric fields. Most crucially, it properly describes superlattices containing an arbitrary number of bulk material layers in the superlattice repeat cycle. Second, the coherent dynamics exhibited by superlattice systems that have been excited by a short laser pulse are described using a wave packet approach. The wave packet description of the superlattice coherent dynamics is an effective means for modelling the interference effects that arise between superlattice subband states that are simultaneously excited by a short laser pulse. A thorough description of both steps of the theoretical formalism is given. We apply the bandstructure calculation technique to the case of a strongly-coupled, quantum well system and the subband energies as a function of well and barrier width are studied. We address processes which invalidate the wave packet description of a system, such as relaxation and decay mechanisms. Finally, the formalism is applied to a number of III-V superlattice systems under short pulse laser excitation. The coherent dynamics of these systems are described. We predict that the wave packets in the superlattice systems display many of the same characteristics as similar wave packets in atomic systems. These include quasi-periodic motion, and the decay and revival of the wave packet. We discuss relevant experimental work and comparisons are made between the experimental results and the appropriate predictions of the wave packet formalism.

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Last modified 13 September 2006