Effects of nonequilibrium phonons on the energy relaxation and recombination lifetime of photogenerated carriers in undoped GaAs quantum wells

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Abstract
Time-resolved and time-integrated photoluminescence studies of an undoped multiple GaAs quantum-well structure excited by 0.5-ps laser pulses have revealed several important experimental observations on the behavior of photoexcited carriers. A large population of nonequilibrium longitudinal optical phonons produced in the energy relaxation process of hot carriers manifests itself by the nonequilibrium phonon-stimulated phonon replica which is located at ∼30 meV below n=1 electron-hole transition. The energy relaxation is substantially suppressed due to the existence of nonequilibrium phonons after an initial rapid cooling (0–5 ps). The number of photoexcited carriers decreases anomalously fast within the first 30 ps after the excitation by laser pulse. An effective carrier depletion time is determined to be as short as 10 ps. A mechanism which leads to such a short carrier depletion time is associated with the nonequilibrium phonon-stimulated phonon replica.