Influence of the kinetic energy of electrons on the formation of excitons in a shallow ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum well

Time-resolved investigations were performed with systematic variation of the excitation energy in order to study the formation of excitons. In a proper designed shallow ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs single quantum well heterostructure an electron system with well-defined kinetic excess energy relative to the excitonic ground state of the quantum well was prepared by photoexcitation and subsequent relaxation via cascaded LO-phonon scattering. Oscillations of the photoluminescence rise time and, in counter phase, a modulation of the decay transient are observed as function of the excitation energy. While the decay time reflects the electron transfer process into the ground state due to different phonon relaxation mechanisms, the rise time reveals an exciton formation process, which depends on the kinetic energy of the electrons. © 1996 The American Physical Society.