Optical and structural properties of metalorganic-vapor-phase-epitaxy-grown InAs quantum wells and quantum dots in InP

InAs single strained quantum wells and nanoclusters have been synthesized by low-pressure metalorganic-vapor-phase epitaxy. The samples were obtained by depositing InAs layers on InP with coverages ranging from several monolayers to a fraction of a monolayer and subsequently overgrowing with InP. These heterostructures were characterized by high-resolution x-ray diffractometry, steady-state and time-resolved photoluminescence, and photoluminescence excitation spectroscopy. In the case of the InAs quantum wells, the experimental x-ray diffraction patterns are in agreement with patterns simulated within the framework of dynamical diffraction theory, assuming that the InAs/InP interfaces are sharp and that the InAs unit cell is tetragonally distorted. The photoluminescence of the quantum wells reveals a series of discrete peaks whose energy positions can be well reproduced by a finite square-well model with a valence-band offset Δ${\mathit{E}}_{\mathrm{hh}}$ of 240 meV. The excitation spectrum of a one-monolayer-thick quantum well exhibits two resonances which are attributed to heavy- and light-hole excitonic transitions. The fractional InAs monolayers were deposited on terraced InP surfaces. Their x-ray diffraction spectra indicate that the InAs nucleates into nanoclusters. A shift toward higher energies of their optical emission is observed and is attributed to a quantum effect caused by lateral confinement of the excitonic wave function. Time-resolved photoluminescence and photoluminescence excitation spectra show that there is enough overlap of the excitonic wave function between adjacent nanoclusters to result in the formation of delocalized excitonic states. The InAs nanoclusters thus form a quantum dot superlattice.