Wave-packet dynamics in quantum wells

A. V. Kuznetsov, G. D. Sanders, C. J. Stanton

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    Abstract

    It has been recently recognized that in bulk semiconductors the displacement current caused by ultrafast optical generation of ''polarized pairs'' in the applied de field is an important mechanism of charge transport in addition to the usual transport current. In quantum-well systems, this polarized pair creation is thought to be the only source of photocurrent at the early stages of photoexcitation since the bulk like transport current is inhibited by the barriers. In this work we perform a full quantum-mechanical analysis of ultrafast optical excitation in a de-biased quantum well. We take into account the multiple transitions that become allowed in the de field which breaks the Delta n = 0 selection rule. As a result, the carriers are created as wave packets formed by coherent superposition of several eigenstates. When the characteristic size of these wave packets (coherence length) is much larger than the well width (for long pulses and/or narrow wells), we recover the polarized pairs behavior of the photocurrent. For shorter pulses, when the coherence length becomes comparable to the well width, the photocurrent exhibits quantum beats. Finally, for very short pulses (around 10 fs) we find that the carriers in a quantum well can behave as an ensemble of classical particles and produce a transport like photocurrent.
    Original languageEnglish
    JournalPhysical Review B Condensed Matter
    Volume52
    Issue number16
    Pages (from-to)12045-12055
    ISSN0163-1829
    DOIs
    Publication statusPublished - 1995

    Bibliographical note

    Copyright (1995) by the American Physical Society.

    Keywords

    • PULSES
    • GENERATION
    • SEMICONDUCTOR SUPERLATTICE
    • PHOTON-ECHO
    • SURFACES
    • HOLE
    • BLOCH OSCILLATIONS
    • EMISSION
    • OPTICAL-EXCITATION
    • VIRTUAL PHOTOCONDUCTIVITY

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