| This thesis concerns the study of the optical properties of ultrathin InAs/InP single quantum wells (QWs) grown by low-pressure metalorganic vapor phase epitaxy (MOCVD). The wells are deposited on Fe-doped (100) semi-insulating InP substrates and have nominal thickness varying between 1 and 4 monolayers (ML). The optical study consist of a series of measurements using Raman scattering, photoluminescence (PL) and photoluminescence excitation (PLE).;The study has revealed that the measured frequencies are in good agreement with those calculated by the ab initio method. Also, contrary to the predictions of the standard model of confined phonons, the observed frequencies vary continuously with InAs thickness. This can be explained by lateral phonon confinement induced by short-scale InAs layer thickness fluctuations.;The fit of the experimental frequencies to the predictions of the standard model leads to a value for the parameter delta lower than the usual one (delta = 1). Ab initio calculations showed in this case that there is a significant penetration of the InAs vibration into the barrier: the first phosphorus atoms located at the interface are not fixed, as they are supposed to be in the standard model for (delta = 1), but vibrate in antiphase with respect to their neighbors.;When the well thickness is higher than dc ≃ 2.4 ML, the Raman spectrum, in parallel with the PL, evolve from single to multiple peak emission. This change is due to 2D/3D growth mode transition which leads to the formation of 3D InAs nanostructures on a wetting layer with a thickness close to 2 ML.;Using Raman scattering, we have been able to observe phonon modes in ultrathin InAs/InP QWs with well thickness as small as one monolayer. These modes are attributed to the first InAs-confined longitudinal optical phonons modes.;Our study shows that even a macroscopic probe such as Raman scattering can provide precise quantitative information on the morphology and the interface structure of ultrathin heterostructures.;On the other hand, the PL study has shown that when the well thickness is lower than dc, the PL contains only one emission peak with a continuous energy shift that does not necessarily correspond to an integer number of ML. The PLE, on the other hand, has shown in this cases discrete variation of hh1 (heavy-hole) and lh1 (light-hole) resonance between 1.22 eV and 1.32 eV and 1.32 eV and 1.37 eV respectively. Taking into account the result obtained from the Raman study these resonances were attributed to 1 ML and 2 ML well thickness, which represent one monolayer less than what was assigned to these resonances in former study. On the other hand when the well thickness is higher than dc, the spectrum consists of a series of peaks whose energy positions are higher than those predicted by calculations. The difference is too large and can not be explained by strain or lateral confinement effect. A phosphorous diffusion in the InAs islands by an As-P exchange can explain this difference.;A PL study as a function of temperature has revealed different behaviors according to whether the well is a complete or incomplete layer with nanostructures on its surface. Anomalous behaviors, such as the decrease of the linewidth and the increase in energy and intensity, was observed with increasing temperature between 20 and 150 K. This was attributed to the thermal reorganization in the occupancy of the various localized states.;Also, the excitation density PL study enabled us to show that the different emission PL peaks cannot originate from excited state emission but rather from InAs islands with different thicknesses.;Finally, low temperature polarization measurements did not reveal any notable polarization effect in the PL spectra. This indicates that the InAs islands are not significantly elongated along the [11¯0] direction. |
