L. Largeau

Temperature-dependent valence band offset and band-gap energies of pseudomorphic GaAsSb on GaAs

The band-gap (Egp) and valence band offset (ΔEv) energies of pseudomorphic GaAsSb layers on GaAs substrate are determined from temperature-dependent photoluminescence measurements on GaAsSb/GaAs and GaAsSb/GaAlAs quantum wells grown by molecular beam epitaxy. A clear evidence of staggered type-II band alignment of GaAsSb relative to GaAs and a value of 1.05 for the valence band offset ratio (Qv) are proposed. Finally, through a detailed comparison of these values with those published previously, we have shown that the scatter in Qv found in the literature (<1 to 2.1) is closely dependent on the exact determination of Egp. Particularly, we have shown that the strain dependence of the deformation potential is important in the calculation of the strain energy contribution to Egp.

Comparison of nitrogen incorporation in molecular-beam epitaxy of GaAsN, GaInAsN, and GaAsSbN

The incorporation of nitrogen in the low percentage range is investigated in a different III–V compound matrix. The materials are grown by molecular-beam epitaxy with a nitrogen radio-frequency plasma source. For equivalent growth conditions, the same rate of N incorporation is found for GaAsN and GaInAsN. However, this N incorporation rate is significantly enhanced in the GaAsSbN alloy. These observations support a discussion on the reactive nitrogen species.

Optical spectroscopy of two-dimensional layered (C6H5C2H4-NH3)2-PbI4 perovskite

We report on optical spectroscopy (photoluminescence and photoluminescence excitation) on two-dimensional self-organized layers of (C(6)H(5)C(2)H(4)-NH(3))(2)-PbI(4) perovskite. Temperature and excitation power dependance of the optical spectra gives a new insight into the excitonic and the phononic properties of this hybrid organic/inorganic semiconductor. In particular, exciton-phonon interaction is found to be more than one order of magnitude higher than in GaAs QWs. As a result, photoluminescence emission lines have to be interpreted in the framework of a polaron model.

GaNAsSb: how does it compare with other dilute III–V-nitride alloys?

Growth and properties of GaNAsSb alloys are investigated and compared with those of other dilute III–N–V alloys. Similar properties are observed including very high bandgap bowing, carrier localization at low temperature, sensitivity to thermal annealing and passivation of N-related electronic states by hydrogen. On the other hand, we point out some features of this alloy system and evaluate its potential for device applications. Probably, GaNAsSb can achieve emission at longer wavelengths than GaInNAs alloys grown to date. Its conduction- and valence-band offsets can be independently tuned by adjusting the N and Sb composition, respectively. Since this compound has a single group III element, its electronic structure should be less dependent on alloy configuration than GaInNAs.

Structural properties of epitaxial SrTiO3 thin films grown by molecular beam epitaxy on Si(001)

This work reports on the structural properties of an epitaxial SrTiO3 (STO) layer grown by molecular beam epitaxy on a Si(001) substrate with a two step process. The study, which includes a complete characterization of large scale plane-view images of the STO layer, is based on a careful analysis of x-ray spectra and transmission electron microscopy images. The STO layer presents a good crystalline quality and a slight texturation related to the presence of extended defects. A thin Ti-rich amorphous silicate layer (thickness ≈1.3nm) is formed at the interface between the STO and the Si substrate, evidencing the thermodynamic instability of the STO/Si interface. The difference between the thermal expansion coefficients of Si and STO is shown to be at the origin of an increased in-plane lattice parameter (3.927A) of the STO layer as compared to its bulk value (3.905A). This effect of differential thermal expansion is expected to be responsible for the formation of at least part of the extended defects of th...

Recent advances in germanium emission [Invited]

The optical properties of germanium can be tailored by combining strain engineering and n-type doping. In this paper, we review the recent progress that has been reported in the study of germanium light emitters for silicon photonics. We discuss the different approaches that were implemented for strain engineering and the issues associated with n-type doping. We show that compact germanium emitters can be obtained by processing germanium into tensile-strained microdisks.

Facet and in-plane crystallographic orientations of GaN nanowires grown on Si(111)

We have determined the in-plane orientation of GaN nanowires relative to the Si (111) substrate on which they were grown. We used x-ray diffraction pole figure measurements to evidence two types of crystallographic orientation, all the nanowires having [Formula: see text] lateral facets. The proportion of these two orientations was determined and shown to be influenced by the pre-deposition of Al(Ga)N intermediate layers. In the main orientation, the GaN basal [Formula: see text] directions are aligned with the [Formula: see text] directions. This orientation corresponds to an in-plane coincidence of GaN and Si lattices.

Structural coherency of epitaxial graphene on 3C-SiC(111) epilayers on Si(111)

Graphene has emerged as a promising nanoelectronic material in electronic devices applications and studying two-dimensional electron gases with relativistic dispersion near Dirac point. Nonetheless, the control of the preparation conditions for homogeneous large-area graphene layers is difficult. Here, we illustrate evidence for high structural and electronic quality epitaxial graphene on 3C-SiC(111). Morphology and electronic structure of the graphene layers have been analyzed with low energy electron microscopy and angle resolved photoemission spectroscopy. Using scanning tunneling microscopy and scanning transmission electron microscopy, we show that graphene exhibits remarkably continuity of step edges suggesting the possibility of growing large scale graphene layer

Wurtzite to zinc blende phase transition in GaAs nanowires induced by epitaxial burying.

We bury vertical free-standing core-shell GaAs/AlGaAs nanowires by a planar GaAs overgrowth. As the nanowires get buried, their crystalline structure progressively transforms: whereas the upper emerging part retains its initial wurtzite structure, the buried part adopts the zinc blende structure of the burying layer. The burying process also suppresses all the stacking faults that existed in the wurtzite nanowires. We consider two possible mechanisms for the structural transition upon burying, examine how they can be discriminated from each other, and explain why the transition is favorable.

Monolithic integration of InP based heterostructures on silicon using crystalline Gd2O3 buffers

A new approach of monolithic integration of InP based heterostructures on silicon is proposed, based on the plastic compliant behavior of the InP/Gd2O3(111) heterointerface. When grown on a crystalline Gd2O3/Si(111) buffer, InP takes its bulk lattice parameter as soon as the growth begins, allowing the monolithic growth of good quality InAsP/InP heterostructures on Si, as attested by room-temperature photoluminescence experiments.