Spectroscopy of the electronic states in InAs quantum dots grown on In _xAl_1-xAs/InP(001)

We have investigated optical properties of high-density InAs self-assembled quantum dots (QDs) in an In_xA1_1-xAs matrix, lattice matched to an InP (001) substrate. The weak lattice mismatch (∼3%) results in a 90% coverage of the In_xAl_1-xAs surface with InAs QDs. By means of interband and intraband spectroscopies crossed with atomic force microscopy (AFM) measurements, we have determined that the InAs QDs optical properties depend on the deposited amount of InAs. Photoinduced absorption spectroscopy has been used to investigate midinfrared intraband absorptions. For three monolayers (ML) InAs deposit thickness, just above two-dimensional (2D)/3D growth mode transition (2.5 ML), the islands form as isolated elliptical dots elongated along the [11̄0] direction and exhibit intraband resonances polarized either along the [110] or the [11̄0] direction. For thicker deposition (>3 ML), InAs islands form chains of elliptical dots along the [11̄0] direction where the quantum confinement is lost, resulting in a quantum-wire-like behavior. In this paper, we also report on photoluminescence and photocurrent spectroscopies, in order to get insight into the InAs/In_xAl_1-xAs island band structure. These experimental results are in good agreement with that of a multiband k·p model.